"ctypes" --- Uma biblioteca de funções externas para Python
***********************************************************

**Código-fonte:** Lib/ctypes

======================================================================

"ctypes" é uma biblioteca de funções externas para Python. Ela fornece
tipos de dados compatíveis com C e permite funções de chamada em DLLs
ou bibliotecas compartilhadas. Ela pode ser usada para agrupar essas
bibliotecas em Python puro.


Tutorial do ctypes
==================

Nota: Os exemplos de código neste tutorial usam "doctest" para
garantir que realmente funcionem. Como algumas amostras de código se
comportam de maneira diferente no Linux, Windows ou macOS, elas contêm
diretrizes de doctest nos comentários.

Nota: Alguns exemplos de código fazem referência ao tipo ctypes
"c_int". Em plataformas em que "sizeof(long) == sizeof(int)" é um
apelido para "c_long". Então, você não deve ficar confuso se "c_long"
for impresso se você esperaria "c_int" --- eles são, na verdade, o
mesmo tipo.


Carregando bibliotecas de ligação dinâmica
------------------------------------------

"ctypes" exporta o *cdll* e, no Windows, os objetos *windll* e
*oledll* para carregar bibliotecas de vínculo dinâmico.

You load libraries by accessing them as attributes of these objects.
*cdll* loads libraries which export functions using the standard
"cdecl" calling convention, while *windll* libraries call functions
using the "stdcall" calling convention. *oledll* also uses the
"stdcall" calling convention, and assumes the functions return a
Windows "HRESULT" error code. The error code is used to automatically
raise an "OSError" exception when the function call fails.

Alterado na versão 3.3: Erros do Windows costumavam levantar
"WindowsError", que agora é um apelido de "OSError".

Here are some examples for Windows. Note that "msvcrt" is the MS
standard C library containing most standard C functions, and uses the
cdecl calling convention:

   >>> from ctypes import *
   >>> print(windll.kernel32)  
   <WinDLL 'kernel32', handle ... at ...>
   >>> print(cdll.msvcrt)      
   <CDLL 'msvcrt', handle ... at ...>
   >>> libc = cdll.msvcrt      
   >>>

O Windows acrescenta automaticamente o sufixo de arquivo ".dll" usual.

Nota:

  Acessar a biblioteca padrão C por meio de "cdll.msvcrt" usará uma
  versão desatualizada da biblioteca, que pode ser incompatível com a
  usada pelo Python. Onde possível, use a funcionalidade nativa do
  Python; caso contrário, importe e use o módulo "msvcrt".

On Linux, it is required to specify the filename *including* the
extension to load a library, so attribute access can not be used to
load libraries. Either the "LoadLibrary()" method of the dll loaders
should be used, or you should load the library by creating an instance
of CDLL by calling the constructor:

   >>> cdll.LoadLibrary("libc.so.6")  
   <CDLL 'libc.so.6', handle ... at ...>
   >>> libc = CDLL("libc.so.6")       
   >>> libc                           
   <CDLL 'libc.so.6', handle ... at ...>
   >>>


Acessando funções de dlls carregadas
------------------------------------

Funções são acessadas como atributos de objetos dll:

   >>> from ctypes import *
   >>> libc.printf
   <_FuncPtr object at 0x...>
   >>> print(windll.kernel32.GetModuleHandleA)  
   <_FuncPtr object at 0x...>
   >>> print(windll.kernel32.MyOwnFunction)     
   Traceback (most recent call last):
     File "<stdin>", line 1, in <module>
     File "ctypes.py", line 239, in __getattr__
       func = _StdcallFuncPtr(name, self)
   AttributeError: function 'MyOwnFunction' not found
   >>>

Note that win32 system dlls like "kernel32" and "user32" often export
ANSI as well as UNICODE versions of a function. The UNICODE version is
exported with an "W" appended to the name, while the ANSI version is
exported with an "A" appended to the name. The win32 "GetModuleHandle"
function, which returns a *module handle* for a given module name, has
the following C prototype, and a macro is used to expose one of them
as "GetModuleHandle" depending on whether UNICODE is defined or not:

   /* ANSI version */
   HMODULE GetModuleHandleA(LPCSTR lpModuleName);
   /* UNICODE version */
   HMODULE GetModuleHandleW(LPCWSTR lpModuleName);

*windll* não tenta selecionar um deles magicamente, você deve acessar
a versão necessária especificando "GetModuleHandleA" ou
"GetModuleHandleW" explicitamente e então chamá-lo com objetos bytes
ou string, respectivamente.

Às vezes, DLLs exportam funções com nomes que não são identificadores
Python válidos, como ""??2@YAPAXI@Z"". Nesse caso, você precisa usar
"getattr()" para recuperar a função:

   >>> getattr(cdll.msvcrt, "??2@YAPAXI@Z")  
   <_FuncPtr object at 0x...>
   >>>

No Windows, algumas dlls exportam funções não por nome, mas por
ordinal. Essas funções podem ser acessadas indexando o objeto dll com
o número ordinal:

   >>> cdll.kernel32[1]  
   <_FuncPtr object at 0x...>
   >>> cdll.kernel32[0]  
   Traceback (most recent call last):
     File "<stdin>", line 1, in <module>
     File "ctypes.py", line 310, in __getitem__
       func = _StdcallFuncPtr(name, self)
   AttributeError: function ordinal 0 not found
   >>>


Chamando funções
----------------

You can call these functions like any other Python callable. This
example uses the "time()" function, which returns system time in
seconds since the Unix epoch, and the "GetModuleHandleA()" function,
which returns a win32 module handle.

This example calls both functions with a "NULL" pointer ("None" should
be used as the "NULL" pointer):

   >>> print(libc.time(None))  
   1150640792
   >>> print(hex(windll.kernel32.GetModuleHandleA(None)))  
   0x1d000000
   >>>

"ValueError" é gerado quando você chama uma função "stdcall" com a
convenção de chamada "cdecl", ou vice-versa:

   >>> cdll.kernel32.GetModuleHandleA(None)  
   Traceback (most recent call last):
     File "<stdin>", line 1, in <module>
   ValueError: Procedure probably called with not enough arguments (4 bytes missing)
   >>>

   >>> windll.msvcrt.printf(b"spam")  
   Traceback (most recent call last):
     File "<stdin>", line 1, in <module>
   ValueError: Procedure probably called with too many arguments (4 bytes in excess)
   >>>

Para descobrir a convenção de chamada correta, você precisa consultar
o arquivo de cabeçalho C ou a documentação da função que deseja
chamar.

No Windows, "ctypes" usa o tratamento de exceções estruturado do win32
para evitar travamentos devido a falhas gerais de proteção quando
funções são chamadas com valores de argumentos inválidos:

   >>> windll.kernel32.GetModuleHandleA(32)  
   Traceback (most recent call last):
     File "<stdin>", line 1, in <module>
   OSError: exception: access violation reading 0x00000020
   >>>

No entanto, existem maneiras suficientes de travar o Python com
"ctypes", então você deve ter cuidado de qualquer maneira. O módulo
"faulthandler" pode ser útil na depuração de travamentos (por exemplo,
de falhas de segmentação produzidas por chamadas errôneas da
biblioteca C).

"None", integers, bytes objects and (unicode) strings are the only
native Python objects that can directly be used as parameters in these
function calls. "None" is passed as a C "NULL" pointer, bytes objects
and strings are passed as pointer to the memory block that contains
their data ("char*" or "wchar_t*").  Python integers are passed as the
platforms default C "int" type, their value is masked to fit into the
C type.

Antes de prosseguirmos com a chamada de funções com outros tipos de
parâmetros, precisamos aprender mais sobre os tipos de dados "ctypes".


Tipos de dados fundamentais
---------------------------

"ctypes" define uma série de tipos de dados primitivos compatíveis com
C:

+------------------------+--------------------------------------------+------------------------------+
| Tipo ctypes            | Tipo em C                                  | Tipo em Python               |
|========================|============================================|==============================|
| "c_bool"               | "_Bool"                                    | bool (1)                     |
+------------------------+--------------------------------------------+------------------------------+
| "c_char"               | "char"                                     | objeto bytes de 1 caractere  |
+------------------------+--------------------------------------------+------------------------------+
| "c_wchar"              | "wchar_t"                                  | string de 1 caractere        |
+------------------------+--------------------------------------------+------------------------------+
| "c_byte"               | "char"                                     | int                          |
+------------------------+--------------------------------------------+------------------------------+
| "c_ubyte"              | "unsigned char"                            | int                          |
+------------------------+--------------------------------------------+------------------------------+
| "c_short"              | "short"                                    | int                          |
+------------------------+--------------------------------------------+------------------------------+
| "c_ushort"             | "unsigned short"                           | int                          |
+------------------------+--------------------------------------------+------------------------------+
| "c_int"                | "int"                                      | int                          |
+------------------------+--------------------------------------------+------------------------------+
| "c_uint"               | "unsigned int"                             | int                          |
+------------------------+--------------------------------------------+------------------------------+
| "c_long"               | "long"                                     | int                          |
+------------------------+--------------------------------------------+------------------------------+
| "c_ulong"              | "unsigned long"                            | int                          |
+------------------------+--------------------------------------------+------------------------------+
| "c_longlong"           | "__int64" ou "long long"                   | int                          |
+------------------------+--------------------------------------------+------------------------------+
| "c_ulonglong"          | "unsigned __int64" ou "unsigned long long" | int                          |
+------------------------+--------------------------------------------+------------------------------+
| "c_size_t"             | "size_t"                                   | int                          |
+------------------------+--------------------------------------------+------------------------------+
| "c_ssize_t"            | "ssize_t" or "Py_ssize_t"                  | int                          |
+------------------------+--------------------------------------------+------------------------------+
| "c_float"              | "float"                                    | ponto flutuante              |
+------------------------+--------------------------------------------+------------------------------+
| "c_double"             | "double"                                   | ponto flutuante              |
+------------------------+--------------------------------------------+------------------------------+
| "c_longdouble"         | "long double"                              | ponto flutuante              |
+------------------------+--------------------------------------------+------------------------------+
| "c_char_p"             | "char*" (finalizado com NUL)               | objeto bytes ou "None"       |
+------------------------+--------------------------------------------+------------------------------+
| "c_wchar_p"            | "wchar_t*" (finalizado com NUL)            | String ou "None"             |
+------------------------+--------------------------------------------+------------------------------+
| "c_void_p"             | "void*"                                    | int ou "None"                |
+------------------------+--------------------------------------------+------------------------------+

1. O construtor aceita qualquer objeto com um valor verdade.

Todos esses tipos podem ser criados chamando-os com um inicializador
opcional do tipo e valor corretos:

   >>> c_int()
   c_long(0)
   >>> c_wchar_p("Hello, World")
   c_wchar_p(140018365411392)
   >>> c_ushort(-3)
   c_ushort(65533)
   >>>

Como esses tipos são mutáveis, seus valores também podem ser alterados
posteriormente:

   >>> i = c_int(42)
   >>> print(i)
   c_long(42)
   >>> print(i.value)
   42
   >>> i.value = -99
   >>> print(i.value)
   -99
   >>>

Assigning a new value to instances of the pointer types "c_char_p",
"c_wchar_p", and "c_void_p" changes the *memory location* they point
to, *not the contents* of the memory block (of course not, because
Python bytes objects are immutable):

   >>> s = "Hello, World"
   >>> c_s = c_wchar_p(s)
   >>> print(c_s)
   c_wchar_p(139966785747344)
   >>> print(c_s.value)
   Hello World
   >>> c_s.value = "Hi, there"
   >>> print(c_s)              # the memory location has changed
   c_wchar_p(139966783348904)
   >>> print(c_s.value)
   Hi, there
   >>> print(s)                # first object is unchanged
   Hello, World
   >>>

No entanto, tome cuidado para não passá-los para funções que esperam
ponteiros para memória mutável. Se precisar de blocos de memória
mutáveis, o ctypes possui uma função "create_string_buffer()" que os
cria de várias maneiras. O conteúdo do bloco de memória atual pode ser
acessado (ou alterado) com a propriedade "raw"; se quiser acessá-lo
como uma string terminada em NUL, use a propriedade "value":

   >>> from ctypes import *
   >>> p = create_string_buffer(3)            # create a 3 byte buffer, initialized to NUL bytes
   >>> print(sizeof(p), repr(p.raw))
   3 b'\x00\x00\x00'
   >>> p = create_string_buffer(b"Hello")     # create a buffer containing a NUL terminated string
   >>> print(sizeof(p), repr(p.raw))
   6 b'Hello\x00'
   >>> print(repr(p.value))
   b'Hello'
   >>> p = create_string_buffer(b"Hello", 10) # create a 10 byte buffer
   >>> print(sizeof(p), repr(p.raw))
   10 b'Hello\x00\x00\x00\x00\x00'
   >>> p.value = b"Hi"
   >>> print(sizeof(p), repr(p.raw))
   10 b'Hi\x00lo\x00\x00\x00\x00\x00'
   >>>

The "create_string_buffer()" function replaces the "c_buffer()"
function (which is still available as an alias), as well as the
"c_string()" function from earlier ctypes releases.  To create a
mutable memory block containing unicode characters of the C type
"wchar_t" use the "create_unicode_buffer()" function.


Chamando funções, continuação
-----------------------------

Observe que printf imprime no canal de saída padrão real, *não* em
"sys.stdout", então esses exemplos só funcionarão no prompt do
console, não de dentro do *IDLE* ou *PythonWin*:

   >>> printf = libc.printf
   >>> printf(b"Hello, %s\n", b"World!")
   Hello, World!
   14
   >>> printf(b"Hello, %S\n", "World!")
   Hello, World!
   14
   >>> printf(b"%d bottles of beer\n", 42)
   42 bottles of beer
   19
   >>> printf(b"%f bottles of beer\n", 42.5)
   Traceback (most recent call last):
     File "<stdin>", line 1, in <module>
   ArgumentError: argument 2: TypeError: Don't know how to convert parameter 2
   >>>

Como mencionado anteriormente, todos os tipos do Python, exceto
inteiros, strings e objetos bytes, precisam ser encapsulados em seu
tipo correspondente de "ctypes", para que possam ser convertidos para
o tipo de dado C necessário:

   >>> printf(b"An int %d, a double %f\n", 1234, c_double(3.14))
   An int 1234, a double 3.140000
   31
   >>>


Chamando funções variadas
-------------------------

Em muitas plataformas, chamar funções variádicas por meio do ctypes é
exatamente o mesmo que chamar funções com um número fixo de
parâmetros. Em algumas plataformas, em particular no ARM64 para
plataformas Apple, a convenção de chamada para funções variádicas
difere da usada para funções regulares.

On those platforms it is required to specify the *argtypes* attribute
for the regular, non-variadic, function arguments:

   libc.printf.argtypes = [ctypes.c_char_p]

Because specifying the attribute does inhibit portability it is
advised to always specify "argtypes" for all variadic functions.


Chamando funções com seus próprios tipos de dados personalizados
----------------------------------------------------------------

You can also customize "ctypes" argument conversion to allow instances
of your own classes be used as function arguments.  "ctypes" looks for
an "_as_parameter_" attribute and uses this as the function argument.
Of course, it must be one of integer, string, or bytes:

   >>> class Bottles:
   ...     def __init__(self, number):
   ...         self._as_parameter_ = number
   ...
   >>> bottles = Bottles(42)
   >>> printf(b"%d bottles of beer\n", bottles)
   42 bottles of beer
   19
   >>>

If you don't want to store the instance's data in the "_as_parameter_"
instance variable, you could define a "property" which makes the
attribute available on request.


Especificando os tipos de argumentos necessários (protótipos de função)
-----------------------------------------------------------------------

It is possible to specify the required argument types of functions
exported from DLLs by setting the "argtypes" attribute.

"argtypes" must be a sequence of C data types (the "printf" function
is probably not a good example here, because it takes a variable
number and different types of parameters depending on the format
string, on the other hand this is quite handy to experiment with this
feature):

   >>> printf.argtypes = [c_char_p, c_char_p, c_int, c_double]
   >>> printf(b"String '%s', Int %d, Double %f\n", b"Hi", 10, 2.2)
   String 'Hi', Int 10, Double 2.200000
   37
   >>>

Especificar um formato protege contra tipos de argumentos
incompatíveis (assim como um protótipo para uma função em C), e tenta
converter os argumentos para tipos válidos:

   >>> printf(b"%d %d %d", 1, 2, 3)
   Traceback (most recent call last):
     File "<stdin>", line 1, in <module>
   ArgumentError: argument 2: TypeError: wrong type
   >>> printf(b"%s %d %f\n", b"X", 2, 3)
   X 2 3.000000
   13
   >>>

If you have defined your own classes which you pass to function calls,
you have to implement a "from_param()" class method for them to be
able to use them in the "argtypes" sequence. The "from_param()" class
method receives the Python object passed to the function call, it
should do a typecheck or whatever is needed to make sure this object
is acceptable, and then return the object itself, its "_as_parameter_"
attribute, or whatever you want to pass as the C function argument in
this case. Again, the result should be an integer, string, bytes, a
"ctypes" instance, or an object with an "_as_parameter_" attribute.


Tipos de Retorno
----------------

By default functions are assumed to return the C "int" type.  Other
return types can be specified by setting the "restype" attribute of
the function object.

Here is a more advanced example, it uses the "strchr" function, which
expects a string pointer and a char, and returns a pointer to a
string:

   >>> strchr = libc.strchr
   >>> strchr(b"abcdef", ord("d"))  
   8059983
   >>> strchr.restype = c_char_p    # c_char_p is a pointer to a string
   >>> strchr(b"abcdef", ord("d"))
   b'def'
   >>> print(strchr(b"abcdef", ord("x")))
   None
   >>>

If you want to avoid the "ord("x")" calls above, you can set the
"argtypes" attribute, and the second argument will be converted from a
single character Python bytes object into a C char:

   >>> strchr.restype = c_char_p
   >>> strchr.argtypes = [c_char_p, c_char]
   >>> strchr(b"abcdef", b"d")
   'def'
   >>> strchr(b"abcdef", b"def")
   Traceback (most recent call last):
     File "<stdin>", line 1, in <module>
   ArgumentError: argument 2: TypeError: one character string expected
   >>> print(strchr(b"abcdef", b"x"))
   None
   >>> strchr(b"abcdef", b"d")
   'def'
   >>>

You can also use a callable Python object (a function or a class for
example) as the "restype" attribute, if the foreign function returns
an integer.  The callable will be called with the *integer* the C
function returns, and the result of this call will be used as the
result of your function call. This is useful to check for error return
values and automatically raise an exception:

   >>> GetModuleHandle = windll.kernel32.GetModuleHandleA  
   >>> def ValidHandle(value):
   ...     if value == 0:
   ...         raise WinError()
   ...     return value
   ...
   >>>
   >>> GetModuleHandle.restype = ValidHandle  
   >>> GetModuleHandle(None)  
   486539264
   >>> GetModuleHandle("something silly")  
   Traceback (most recent call last):
     File "<stdin>", line 1, in <module>
     File "<stdin>", line 3, in ValidHandle
   OSError: [Errno 126] The specified module could not be found.
   >>>

"WinError" é uma função que chamará a API "FormatMessage()" do Windows
para obter a representação em string de um código de erro, e *retorna*
uma exceção.  "WinError" aceita um parâmetro de código de erro
opcional, se nenhum for usado, ela chama "GetLastError()" para
recuperá-lo.

Please note that a much more powerful error checking mechanism is
available through the "errcheck" attribute; see the reference manual
for details.


Passando ponteiros (ou: passando parâmetros por referência)
-----------------------------------------------------------

Às vezes, uma função da API C espera um *ponteiro* para um tipo de
dado como parâmetro, provavelmente para escrever no local
correspondente, ou se os dados forem muito grandes para serem passados
por valor. Isso também é conhecido como *passar parâmetros por
referência*.

O "ctypes" exporta a função "byref()" que é usada para passar
parâmetros por referência. O mesmo efeito pode ser alcançado com a
função "pointer()", embora "pointer()" faça muito mais trabalho, já
que ela constrói um objeto ponteiro real, então é mais rápido usar
"byref()" se você não precisar do objeto ponteiro no próprio Python:

   >>> i = c_int()
   >>> f = c_float()
   >>> s = create_string_buffer(b'\000' * 32)
   >>> print(i.value, f.value, repr(s.value))
   0 0.0 b''
   >>> libc.sscanf(b"1 3.14 Hello", b"%d %f %s",
   ...             byref(i), byref(f), s)
   3
   >>> print(i.value, f.value, repr(s.value))
   1 3.1400001049 b'Hello'
   >>>


Estruturas e uniões
-------------------

Structures and unions must derive from the "Structure" and "Union"
base classes which are defined in the "ctypes" module. Each subclass
must define a "_fields_" attribute.  "_fields_" must be a list of
*2-tuples*, containing a *field name* and a *field type*.

O tipo do campo deve ser um tipo "ctypes" como "c_int", ou qualquer
outro tipo "ctypes" derivado: estrutura, união, array, ponteiro.

Aqui está um exemplo simples de uma estrutura POINT, que contém dois
inteiros nomeados *x* e *y*, e também mostra como inicializar uma
estrutura no construtor:

   >>> from ctypes import *
   >>> class POINT(Structure):
   ...     _fields_ = [("x", c_int),
   ...                 ("y", c_int)]
   ...
   >>> point = POINT(10, 20)
   >>> print(point.x, point.y)
   10 20
   >>> point = POINT(y=5)
   >>> print(point.x, point.y)
   0 5
   >>> POINT(1, 2, 3)
   Traceback (most recent call last):
     File "<stdin>", line 1, in <module>
   TypeError: too many initializers
   >>>

Você pode, no entanto, construir estruturas muito mais complicadas.
Uma estrutura pode conter outras estruturas, usando uma estrutura como
um tipo de campo.

Aqui está uma estrutura RECT que contém dois POINTs nomeados
*upperleft* e *lowerright*:

   >>> class RECT(Structure):
   ...     _fields_ = [("upperleft", POINT),
   ...                 ("lowerright", POINT)]
   ...
   >>> rc = RECT(point)
   >>> print(rc.upperleft.x, rc.upperleft.y)
   0 5
   >>> print(rc.lowerright.x, rc.lowerright.y)
   0 0
   >>>

Estruturas aninhadas também podem ser inicializadas no construtor de
várias maneiras:

   >>> r = RECT(POINT(1, 2), POINT(3, 4))
   >>> r = RECT((1, 2), (3, 4))

Field *descriptor*s can be retrieved from the *class*, they are useful
for debugging because they can provide useful information:

   >>> print(POINT.x)
   <Field type=c_long, ofs=0, size=4>
   >>> print(POINT.y)
   <Field type=c_long, ofs=4, size=4>
   >>>

Aviso:

  O "ctypes" não suporta passar uniões ou estruturas com campos de
  bits (bit-fields) para funções por valor. Embora isso possa
  funcionar em x86 de 32 bits, não é garantido pela biblioteca que
  funcione no caso geral. Uniões e estruturas com campos de bits devem
  sempre ser passadas para funções por ponteiro.


Structure/union alignment and byte order
----------------------------------------

By default, Structure and Union fields are aligned in the same way the
C compiler does it. It is possible to override this behavior by
specifying a "_pack_" class attribute in the subclass definition. This
must be set to a positive integer and specifies the maximum alignment
for the fields. This is what "#pragma pack(n)" also does in MSVC.

"ctypes" usa a ordem de bytes nativa para Estruturas e Uniões. Para
construir estruturas com ordem de bytes não nativa, você pode usar
classes base "BigEndianStructure", "LittleEndianStructure",
"BigEndianUnion" e "LittleEndianUnion". Essas classes não podem conter
campos de ponteiros.


Campos de bit em estruturas e uniões
------------------------------------

It is possible to create structures and unions containing bit fields.
Bit fields are only possible for integer fields, the bit width is
specified as the third item in the "_fields_" tuples:

   >>> class Int(Structure):
   ...     _fields_ = [("first_16", c_int, 16),
   ...                 ("second_16", c_int, 16)]
   ...
   >>> print(Int.first_16)
   <Field type=c_long, ofs=0:0, bits=16>
   >>> print(Int.second_16)
   <Field type=c_long, ofs=0:16, bits=16>
   >>>


Vetores
-------

Vetores são sequências que contêm um número fixo de instâncias do
mesmo tipo.

A maneira recomendada de criar tipos vetor é multiplicando um tipo de
dado por um inteiro positivo:

   TenPointsArrayType = POINT * 10

Aqui está um exemplo de um tipo de dado um tanto artificial, uma
estrutura contendo 4 POINTs entre outras coisas:

   >>> from ctypes import *
   >>> class POINT(Structure):
   ...     _fields_ = ("x", c_int), ("y", c_int)
   ...
   >>> class MyStruct(Structure):
   ...     _fields_ = [("a", c_int),
   ...                 ("b", c_float),
   ...                 ("point_array", POINT * 4)]
   >>>
   >>> print(len(MyStruct().point_array))
   4
   >>>

Instâncias são criadas da maneira usual, chamando a classe:

   arr = TenPointsArrayType()
   for pt in arr:
       print(pt.x, pt.y)

O código acima exibe uma série de linhas "0 0", pois o conteúdo do
vetor é inicializado com zeros.

Inicializadores do tipo correto também podem ser especificados:

   >>> from ctypes import *
   >>> TenIntegers = c_int * 10
   >>> ii = TenIntegers(1, 2, 3, 4, 5, 6, 7, 8, 9, 10)
   >>> print(ii)
   <c_long_Array_10 object at 0x...>
   >>> for i in ii: print(i, end=" ")
   ...
   1 2 3 4 5 6 7 8 9 10
   >>>


Ponteiros
---------

Instâncias de ponteiro são criadas chamando a função "pointer()" em um
tipo "ctypes":

   >>> from ctypes import *
   >>> i = c_int(42)
   >>> pi = pointer(i)
   >>>

Instâncias de ponteiros têm um atributo "contents" que retorna o
objeto para qual o ponteiro aponta, o objeto "i" acima:

   >>> pi.contents
   c_long(42)
   >>>

Note que o "ctypes" não possui OOR (retorno de objeto original), ele
constrói um objeto novo e equivalente cada vez que você recupera um
atributo:

   >>> pi.contents is i
   False
   >>> pi.contents is pi.contents
   False
   >>>

Atribuir outra instância "c_int" ao atributo do conteúdo do ponteiro
faria com que o ponteiro apontasse para o local de memória onde ela
está armazenada:

   >>> i = c_int(99)
   >>> pi.contents = i
   >>> pi.contents
   c_long(99)
   >>>

Instâncias de ponteiro também podem ser indexadas com inteiros:

   >>> pi[0]
   99
   >>>

Atribuir a um índice inteiro altera o valor apontado:

   >>> print(i)
   c_long(99)
   >>> pi[0] = 22
   >>> print(i)
   c_long(22)
   >>>

Também é possível usar índices diferentes de 0, mas você deve saber o
que está fazendo, assim como em C: Você pode acessar ou alterar locais
arbitrários da memória. Geralmente, você só usa este recurso se
receber um ponteiro de uma função C, e você *sabe* que o ponteiro na
verdade aponta para um vetor em vez de um único item.

Nos bastidores, a função "pointer()" faz mais do que simplesmente
criar instâncias de ponteiro, ela precisa criar *tipos* de ponteiro
primeiro. Isso é feito com a função "POINTER()", que aceita qualquer
tipo "ctypes", e retorna um novo tipo:

   >>> PI = POINTER(c_int)
   >>> PI
   <class 'ctypes.LP_c_long'>
   >>> PI(42)
   Traceback (most recent call last):
     File "<stdin>", line 1, in <module>
   TypeError: expected c_long instead of int
   >>> PI(c_int(42))
   <ctypes.LP_c_long object at 0x...>
   >>>

Chamar o tipo ponteiro sem um argumento cria um ponteiro "NULL".
Ponteiros "NULL" possuem o valor booleano "False":

   >>> null_ptr = POINTER(c_int)()
   >>> print(bool(null_ptr))
   False
   >>>

O "ctypes" verifica por "NULL" ao desreferenciar ponteiros (mas
desreferenciar ponteiros inválidos que não sejam "NULL" travaria o
Python):

   >>> null_ptr[0]
   Traceback (most recent call last):
       ....
   ValueError: NULL pointer access
   >>>

   >>> null_ptr[0] = 1234
   Traceback (most recent call last):
       ....
   ValueError: NULL pointer access
   >>>


Conversão de Tipos
------------------

Usually, ctypes does strict type checking.  This means, if you have
"POINTER(c_int)" in the "argtypes" list of a function or as the type
of a member field in a structure definition, only instances of exactly
the same type are accepted.  There are some exceptions to this rule,
where ctypes accepts other objects.  For example, you can pass
compatible array instances instead of pointer types.  So, for
"POINTER(c_int)", ctypes accepts an array of c_int:

   >>> class Bar(Structure):
   ...     _fields_ = [("count", c_int), ("values", POINTER(c_int))]
   ...
   >>> bar = Bar()
   >>> bar.values = (c_int * 3)(1, 2, 3)
   >>> bar.count = 3
   >>> for i in range(bar.count):
   ...     print(bar.values[i])
   ...
   1
   2
   3
   >>>

In addition, if a function argument is explicitly declared to be a
pointer type (such as "POINTER(c_int)") in "argtypes", an object of
the pointed type ("c_int" in this case) can be passed to the function.
ctypes will apply the required "byref()" conversion in this case
automatically.

Para definir um campo do tipo PONTEIRO como "NULL", você pode atribuir
"None":

   >>> bar.values = None
   >>>

Às vezes, você tem instâncias de tipos incompatíveis. Em C, você pode
converter um tipo em outro tipo. O "ctypes" fornece uma função
"cast()" que pode ser usada da mesma maneira. A estrutura "Bar"
definida acima aceita ponteiros "POINTER(c_int)" ou vetores "c_int"
para seu campo "values", mas não instâncias de outros tipos:

   >>> bar.values = (c_byte * 4)()
   Traceback (most recent call last):
     File "<stdin>", line 1, in <module>
   TypeError: incompatible types, c_byte_Array_4 instance instead of LP_c_long instance
   >>>

Para esses casos, a função "cast()" é útil.

A função "cast()" pode ser usada para converter uma instância ctypes
em um ponteiro para um diferente tipo de dado ctypes. "cast()" recebe
dois parâmetros, um objeto ctypes que é ou pode ser convertido para um
ponteiro de algum tipo, e um tipo ponteiro ctypes. Ela retorna uma
instância do segundo argumento, que referencia o mesmo bloco de
memória que o primeiro argumento:

   >>> a = (c_byte * 4)()
   >>> cast(a, POINTER(c_int))
   <ctypes.LP_c_long object at ...>
   >>>

Então, "cast()" pode ser usada para atribuir ao campo "values" da
estrutura "Bar":

   >>> bar = Bar()
   >>> bar.values = cast((c_byte * 4)(), POINTER(c_int))
   >>> print(bar.values[0])
   0
   >>>


Tipos Incompletos
-----------------

*Tipos Incompletos* são estruturas, uniões ou vetores, cujos membros
ainda não foram especificados. Em C, eles são especificados por
declarações antecipadas, que são definidas posteriormente:

   struct cell; /* forward declaration */

   struct cell {
       char *name;
       struct cell *next;
   };

A tradução direta para código ctypes seria esta, mas não funciona:

   >>> class cell(Structure):
   ...     _fields_ = [("name", c_char_p),
   ...                 ("next", POINTER(cell))]
   ...
   Traceback (most recent call last):
     File "<stdin>", line 1, in <module>
     File "<stdin>", line 2, in cell
   NameError: name 'cell' is not defined
   >>>

because the new "class cell" is not available in the class statement
itself. In "ctypes", we can define the "cell" class and set the
"_fields_" attribute later, after the class statement:

   >>> from ctypes import *
   >>> class cell(Structure):
   ...     pass
   ...
   >>> cell._fields_ = [("name", c_char_p),
   ...                  ("next", POINTER(cell))]
   >>>

Vamos tentar. Criamos duas instâncias de "cell", e deixamos que elas
apontem uma para a outra, e finalmente seguimos a cadeia de ponteiros
algumas vezes:

   >>> c1 = cell()
   >>> c1.name = b"foo"
   >>> c2 = cell()
   >>> c2.name = b"bar"
   >>> c1.next = pointer(c2)
   >>> c2.next = pointer(c1)
   >>> p = c1
   >>> for i in range(8):
   ...     print(p.name, end=" ")
   ...     p = p.next[0]
   ...
   foo bar foo bar foo bar foo bar
   >>>


Funções Callbacks
-----------------

"ctypes" permite criar ponteiros de função C chamáveis a partir de
chamáveis Python. Estas são às vezes chamadas de *funções de callback*

Primeiro, você deve criar uma classe para função de retorno. A classe
sabe a convenção de chamada , o tipo de retorno, e o número e tipos de
argumentos que essa função irá receber.

A função de fábrica "CFUNCTYPE()" cria tipos para funções de retorno
usando a convenção de chamada "cdecl". No Windows, a função de fábrica
"WINFUNCTYPE()" cria tipos para funções de retorno usando a convenção
de chamada "stdcall".

Ambas estas funções de fábrica são chamadas com o tipo de resultado
como primeiro argumento, e os tipos de argumento esperados da função
de retorno como os argumentos restantes.

I will present an example here which uses the standard C library's
"qsort()" function, that is used to sort items with the help of a
callback function.  "qsort()" will be used to sort an array of
integers:

   >>> IntArray5 = c_int * 5
   >>> ia = IntArray5(5, 1, 7, 33, 99)
   >>> qsort = libc.qsort
   >>> qsort.restype = None
   >>>

"qsort()" must be called with a pointer to the data to sort, the
number of items in the data array, the size of one item, and a pointer
to the comparison function, the callback. The callback will then be
called with two pointers to items, and it must return a negative
integer if the first item is smaller than the second, a zero if they
are equal, and a positive integer otherwise.

Então, nossa função de retorno (callback function) recebe ponteiros
para inteiros, e deve retornar um inteiro. Primeiro criamos o "type"
para a função de retorno:

   >>> CMPFUNC = CFUNCTYPE(c_int, POINTER(c_int), POINTER(c_int))
   >>>

Para começar, aqui está uma função de retorno (callback) simples que
mostra os valores que lhe são passados:

   >>> def py_cmp_func(a, b):
   ...     print("py_cmp_func", a[0], b[0])
   ...     return 0
   ...
   >>> cmp_func = CMPFUNC(py_cmp_func)
   >>>

O resultado:

   >>> qsort(ia, len(ia), sizeof(c_int), cmp_func)  
   py_cmp_func 5 1
   py_cmp_func 33 99
   py_cmp_func 7 33
   py_cmp_func 5 7
   py_cmp_func 1 7
   >>>

Agora podemos realmente comparar os dois itens e retornar um resultado
útil:

   >>> def py_cmp_func(a, b):
   ...     print("py_cmp_func", a[0], b[0])
   ...     return a[0] - b[0]
   ...
   >>>
   >>> qsort(ia, len(ia), sizeof(c_int), CMPFUNC(py_cmp_func)) 
   py_cmp_func 5 1
   py_cmp_func 33 99
   py_cmp_func 7 33
   py_cmp_func 1 7
   py_cmp_func 5 7
   >>>

Como podemos verificar facilmente, nosso vetor está ordenado agora:

   >>> for i in ia: print(i, end=" ")
   ...
   1 5 7 33 99
   >>>

As fábricas de funções podem ser usadas como fábricas de decoradores,
então também podemos escrever:

   >>> @CFUNCTYPE(c_int, POINTER(c_int), POINTER(c_int))
   ... def py_cmp_func(a, b):
   ...     print("py_cmp_func", a[0], b[0])
   ...     return a[0] - b[0]
   ...
   >>> qsort(ia, len(ia), sizeof(c_int), py_cmp_func)
   py_cmp_func 5 1
   py_cmp_func 33 99
   py_cmp_func 7 33
   py_cmp_func 1 7
   py_cmp_func 5 7
   >>>

Nota:

  Certifique-se de manter referências aos objetos "CFUNCTYPE()"
  enquanto eles forem usados a partir do código C. O "ctypes" não faz
  isso, e se você não o fizer, eles podem ser coletados pelo coletor
  de lixo, travando seu programa quando uma função de retorno é
  chamada.Além disso, note que se a função de retorno for chamada em
  uma thread criada fora do controle do Python (por exemplo, pelo
  código externo que chama a função de retorno), o ctypes cria uma
  nova thread Python "dummy" (fictícia) em cada invocação. Este
  comportamento é correto para a maioria dos propósitos, mas significa
  que os valores armazenados com "threading.local" *não* sobreviverão
  entre diferentes funções de retorno, mesmo quando essas chamadas são
  feitas a partir da mesma thread C.


Acessando valores exportados de dlls
------------------------------------

Some shared libraries not only export functions, they also export
variables. An example in the Python library itself is the
"Py_OptimizeFlag", an integer set to 0, 1, or 2, depending on the "-O"
or "-OO" flag given on startup.

"ctypes" can access values like this with the "in_dll()" class methods
of the type.  *pythonapi* is a predefined symbol giving access to the
Python C api:

   >>> opt_flag = c_int.in_dll(pythonapi, "Py_OptimizeFlag")
   >>> print(opt_flag)
   c_long(0)
   >>>

If the interpreter would have been started with "-O", the sample would
have printed "c_long(1)", or "c_long(2)" if "-OO" would have been
specified.

Um exemplo estendido que também demonstra o uso de ponteiros acessa o
ponteiro "PyImport_FrozenModules" exportado pelo Python.

Citando a documentação para esse valor:

   Este ponteiro é inicializado para apontar para um vetor de
   registros de "_frozen", terminado por um cujos membros são todos
   "NULL" ou zero. Quando um módulo congelado é importado, ele é
   pesquisado nesta tabela. O código de terceiros pode fazer truques
   com isso para fornecer uma coleção criada dinamicamente de módulos
   congelados.

Então, manipular este ponteiro pode até ser útil. Para restringir o
tamanho do exemplo, mostramos apenas como esta tabela pode ser lida
com "ctypes":

   >>> from ctypes import *
   >>>
   >>> class struct_frozen(Structure):
   ...     _fields_ = [("name", c_char_p),
   ...                 ("code", POINTER(c_ubyte)),
   ...                 ("size", c_int)]
   ...
   >>>

Nós definimos tipo de dado "_frozen", para que possamos obter o
ponteiro para a tabela:

   >>> FrozenTable = POINTER(struct_frozen)
   >>> table = FrozenTable.in_dll(pythonapi, "PyImport_FrozenModules")
   >>>

Como "table" é um "pointer" para o vetor de registros "struct_frozen",
nós podemos iterar sobre ele, mas só temos que nos certificar de que
nosso loop termine, porque ponteiros não têm tamanho. Cedo ou tarde,
ele provavelmente travaria com uma violação de acesso ou algo assim,
então é melhor sair do loop quando atingirmos a entrada "NULL":

   >>> for item in table:
   ...     if item.name is None:
   ...         break
   ...     print(item.name.decode("ascii"), item.size)
   ...
   _frozen_importlib 31764
   _frozen_importlib_external 41499
   __hello__ 161
   __phello__ -161
   __phello__.spam 161
   >>>

O fato de que o Python padrão tem um módulo congelado e um pacote
congelado (indicado pelo membro "size" negativo) não é bem conhecido,
é usado apenas para testes. Experimente com "import __hello__" por
exemplo.


Surpresas
---------

Existem algumas pontos limites no "ctypes" onde você pode esperar algo
diferente do que realmente ocorre.

Considere o exemplo a seguir:

   >>> from ctypes import *
   >>> class POINT(Structure):
   ...     _fields_ = ("x", c_int), ("y", c_int)
   ...
   >>> class RECT(Structure):
   ...     _fields_ = ("a", POINT), ("b", POINT)
   ...
   >>> p1 = POINT(1, 2)
   >>> p2 = POINT(3, 4)
   >>> rc = RECT(p1, p2)
   >>> print(rc.a.x, rc.a.y, rc.b.x, rc.b.y)
   1 2 3 4
   >>> # now swap the two points
   >>> rc.a, rc.b = rc.b, rc.a
   >>> print(rc.a.x, rc.a.y, rc.b.x, rc.b.y)
   3 4 3 4
   >>>

Hm. Nós com certeza esperávamos que a última instrução exibisse "3 4 1
2". O que aconteceu? Aqui estão os passos da linha "rc.a, rc.b = rc.b,
rc.a" acima:

   >>> temp0, temp1 = rc.b, rc.a
   >>> rc.a = temp0
   >>> rc.b = temp1
   >>>

Observe que "temp0" e "temp1" ainda são objetos que utilizam o buffer
interno do objeto "rc" acima. Portanto, executar "rc.a = temp0" copia
o conteúdo do buffer de "temp0" para o buffer de "rc". Isso, por sua
vez, altera o conteúdo de "temp1". Assim, a última atribuição "rc.b =
temp1" não produz o efeito esperado.

Tenha em mente que obter sub-objetos de estruturas, uniões e vetores
não copia o sub-objeto; em vez disso, recupera um objeto de
encapsulamento (wrapper) que acessa o buffer subjacente do objeto
raiz.

Outro exemplo que pode se comportar de maneira diferente do que alguém
poderia esperar é o seguinte:

   >>> s = c_char_p()
   >>> s.value = b"abc def ghi"
   >>> s.value
   b'abc def ghi'
   >>> s.value is s.value
   False
   >>>

Nota:

  Objetos instanciados a partir de "c_char_p" só podem ter seu valor
  definido para bytes ou inteiros.

Por que está imprimindo "False"? Instâncias de ctypes são objetos que
contêm um bloco de memória, além de alguns *descriptor*s que acessam o
conteúdo dessa memória. Armazenar um objeto Python no bloco de memória
não armazena o próprio objeto; em vez disso, armazena-se o seu
atributo "contents". Acessar o contents novamente constrói um novo
objeto Python a cada vez!


Tipos de dados de tamanho variável
----------------------------------

O "ctypes" fornece algum suporte para vetores e estruturas de tamanhos
variável.

A função "resize()" pode ser usada para redimensionar o buffer de
memória de um objeto ctypes existente. A função recebe o objeto como
primeiro argumento, e o tamanho solicitado em bytes como o segundo
argumento. O bloco de memória não pode ser tornado menor do que o
bloco de memória natural especificado pelo tipo do objeto, um
"ValueError" é levantado se isso for tentado:

   >>> short_array = (c_short * 4)()
   >>> print(sizeof(short_array))
   8
   >>> resize(short_array, 4)
   Traceback (most recent call last):
       ...
   ValueError: minimum size is 8
   >>> resize(short_array, 32)
   >>> sizeof(short_array)
   32
   >>> sizeof(type(short_array))
   8
   >>>

Isso é bom e funcional, mas como alguém acessaria os elementos
contidos neste vetor? Já que o tipo ainda sabe apenas sobre 4
elementos, obtemos erros ao acessar outros elementos:

   >>> short_array[:]
   [0, 0, 0, 0]
   >>> short_array[7]
   Traceback (most recent call last):
       ...
   IndexError: invalid index
   >>>

Outra maneira de usar tipos de dados de tamanho variável com o
"ctypes" é usar a natureza dinâmica do Python, e (re)definir o tipo de
dados  depois que o tamanho necessário já for conhecido, caso a caso.


Referência ctypes
=================


Encontrando bibliotecas compartilhadas
--------------------------------------

Ao programar em uma linguagem compilada, bibliotecas compartilhadas
são acessadas ao compilar/linkar (compiling/linking) um programa, e
quando o programa é executado.

The purpose of the "find_library()" function is to locate a library in
a way similar to what the compiler or runtime loader does (on
platforms with several versions of a shared library the most recent
should be loaded), while the ctypes library loaders act like when a
program is run, and call the runtime loader directly.

The "ctypes.util" module provides a function which can help to
determine the library to load.

ctypes.util.find_library(name)

   Try to find a library and return a pathname.  *name* is the library
   name without any prefix like *lib*, suffix like ".so", ".dylib" or
   version number (this is the form used for the posix linker option
   "-l").  If no library can be found, returns "None".

The exact functionality is system dependent.

On Linux, "find_library()" tries to run external programs
("/sbin/ldconfig", "gcc", "objdump" and "ld") to find the library
file. It returns the filename of the library file.

Alterado na versão 3.6: On Linux, the value of the environment
variable "LD_LIBRARY_PATH" is used when searching for libraries, if a
library cannot be found by any other means.

Veja alguns exemplos:

   >>> from ctypes.util import find_library
   >>> find_library("m")
   'libm.so.6'
   >>> find_library("c")
   'libc.so.6'
   >>> find_library("bz2")
   'libbz2.so.1.0'
   >>>

On macOS, "find_library()" tries several predefined naming schemes and
paths to locate the library, and returns a full pathname if
successful:

   >>> from ctypes.util import find_library
   >>> find_library("c")
   '/usr/lib/libc.dylib'
   >>> find_library("m")
   '/usr/lib/libm.dylib'
   >>> find_library("bz2")
   '/usr/lib/libbz2.dylib'
   >>> find_library("AGL")
   '/System/Library/Frameworks/AGL.framework/AGL'
   >>>

On Windows, "find_library()" searches along the system search path,
and returns the full pathname, but since there is no predefined naming
scheme a call like "find_library("c")" will fail and return "None".

If wrapping a shared library with "ctypes", it *may* be better to
determine the shared library name at development time, and hardcode
that into the wrapper module instead of using "find_library()" to
locate the library at runtime.


Loading shared libraries
------------------------

There are several ways to load shared libraries into the Python
process.  One way is to instantiate one of the following classes:

class ctypes.CDLL(name, mode=DEFAULT_MODE, handle=None, use_errno=False, use_last_error=False, winmode=None)

   Instances of this class represent loaded shared libraries.
   Functions in these libraries use the standard C calling convention,
   and are assumed to return "int".

   On Windows creating a "CDLL" instance may fail even if the DLL name
   exists. When a dependent DLL of the loaded DLL is not found, a
   "OSError" error is raised with the message *"[WinError 126] The
   specified module could not be found".* This error message does not
   contain the name of the missing DLL because the Windows API does
   not return this information making this error hard to diagnose. To
   resolve this error and determine which DLL is not found, you need
   to find the list of dependent DLLs and determine which one is not
   found using Windows debugging and tracing tools.

Ver também: Microsoft DUMPBIN tool -- A tool to find DLL dependents.

class ctypes.OleDLL(name, mode=DEFAULT_MODE, handle=None, use_errno=False, use_last_error=False, winmode=None)

   Windows only: Instances of this class represent loaded shared
   libraries, functions in these libraries use the "stdcall" calling
   convention, and are assumed to return the windows specific
   "HRESULT" code.  "HRESULT" values contain information specifying
   whether the function call failed or succeeded, together with
   additional error code.  If the return value signals a failure, an
   "OSError" is automatically raised.

   Alterado na versão 3.3: "WindowsError" used to be raised.

class ctypes.WinDLL(name, mode=DEFAULT_MODE, handle=None, use_errno=False, use_last_error=False, winmode=None)

   Windows only: Instances of this class represent loaded shared
   libraries, functions in these libraries use the "stdcall" calling
   convention, and are assumed to return "int" by default.

The Python *global interpreter lock* is released before calling any
function exported by these libraries, and reacquired afterwards.

class ctypes.PyDLL(name, mode=DEFAULT_MODE, handle=None)

   Instâncias desta classe se comportam como instâncias "CDLL", exceto
   que o GIL do Python *não* é liberado durante a chamada da função e,
   após a execução da função, o sinalizador de erro do Python é
   verificado. Se o sinalizador de erro estiver definido, uma exceção
   Python é levantada.

   Portanto, isso só é útil para chamar funções da api C do Python
   diretamente.

All these classes can be instantiated by calling them with at least
one argument, the pathname of the shared library.  If you have an
existing handle to an already loaded shared library, it can be passed
as the "handle" named parameter, otherwise the underlying platforms
"dlopen" or "LoadLibrary" function is used to load the library into
the process, and to get a handle to it.

O parâmetro *mode* pode ser utilizado para especificar como a
biblioteca é carregada. Para detalhes, consulte a página de manual
*dlopen(3)*. No Windows, *mode* é ignorado. Em sistemas posix,
RTLD_NOW é sempre adicionado e, não é configurável.

The *use_errno* parameter, when set to true, enables a ctypes
mechanism that allows accessing the system "errno" error number in a
safe way. "ctypes" maintains a thread-local copy of the systems
"errno" variable; if you call foreign functions created with
"use_errno=True" then the "errno" value before the function call is
swapped with the ctypes private copy, the same happens immediately
after the function call.

The function "ctypes.get_errno()" returns the value of the ctypes
private copy, and the function "ctypes.set_errno()" changes the ctypes
private copy to a new value and returns the former value.

The *use_last_error* parameter, when set to true, enables the same
mechanism for the Windows error code which is managed by the
"GetLastError()" and "SetLastError()" Windows API functions;
"ctypes.get_last_error()" and "ctypes.set_last_error()" are used to
request and change the ctypes private copy of the windows error code.

The *winmode* parameter is used on Windows to specify how the library
is loaded (since *mode* is ignored). It takes any value that is valid
for the Win32 API "LoadLibraryEx" flags parameter. When omitted, the
default is to use the flags that result in the most secure DLL load to
avoiding issues such as DLL hijacking. Passing the full path to the
DLL is the safest way to ensure the correct library and dependencies
are loaded.

Alterado na versão 3.8: Added *winmode* parameter.

ctypes.RTLD_GLOBAL

   Flag to use as *mode* parameter.  On platforms where this flag is
   not available, it is defined as the integer zero.

ctypes.RTLD_LOCAL

   Flag to use as *mode* parameter.  On platforms where this is not
   available, it is the same as *RTLD_GLOBAL*.

ctypes.DEFAULT_MODE

   The default mode which is used to load shared libraries.  On OSX
   10.3, this is *RTLD_GLOBAL*, otherwise it is the same as
   *RTLD_LOCAL*.

Instances of these classes have no public methods.  Functions exported
by the shared library can be accessed as attributes or by index.
Please note that accessing the function through an attribute caches
the result and therefore accessing it repeatedly returns the same
object each time.  On the other hand, accessing it through an index
returns a new object each time:

   >>> from ctypes import CDLL
   >>> libc = CDLL("libc.so.6")  # On Linux
   >>> libc.time == libc.time
   True
   >>> libc['time'] == libc['time']
   False

The following public attributes are available, their name starts with
an underscore to not clash with exported function names:

PyDLL._handle

   The system handle used to access the library.

PyDLL._name

   The name of the library passed in the constructor.

Shared libraries can also be loaded by using one of the prefabricated
objects, which are instances of the "LibraryLoader" class, either by
calling the "LoadLibrary()" method, or by retrieving the library as
attribute of the loader instance.

class ctypes.LibraryLoader(dlltype)

   Class which loads shared libraries.  *dlltype* should be one of the
   "CDLL", "PyDLL", "WinDLL", or "OleDLL" types.

   "__getattr__()" has special behavior: It allows loading a shared
   library by accessing it as attribute of a library loader instance.
   The result is cached, so repeated attribute accesses return the
   same library each time.

   LoadLibrary(name)

      Load a shared library into the process and return it.  This
      method always returns a new instance of the library.

These prefabricated library loaders are available:

ctypes.cdll

   Creates "CDLL" instances.

ctypes.windll

   Windows only: Creates "WinDLL" instances.

ctypes.oledll

   Windows only: Creates "OleDLL" instances.

ctypes.pydll

   Creates "PyDLL" instances.

For accessing the C Python api directly, a ready-to-use Python shared
library object is available:

ctypes.pythonapi

   An instance of "PyDLL" that exposes Python C API functions as
   attributes.  Note that all these functions are assumed to return C
   "int", which is of course not always the truth, so you have to
   assign the correct "restype" attribute to use these functions.

Levanta um evento de auditoria "ctypes.dlopen" com o argumento "name".

Accessing a function on a loaded library raises an auditing event
"ctypes.dlsym" with arguments "library" (the library object) and
"name" (the symbol's name as a string or integer).

In cases when only the library handle is available rather than the
object, accessing a function raises an auditing event
"ctypes.dlsym/handle" with arguments "handle" (the raw library handle)
and "name".


Foreign functions
-----------------

As explained in the previous section, foreign functions can be
accessed as attributes of loaded shared libraries.  The function
objects created in this way by default accept any number of arguments,
accept any ctypes data instances as arguments, and return the default
result type specified by the library loader. They are instances of a
private class:

class ctypes._FuncPtr

   Base class for C callable foreign functions.

   Instances of foreign functions are also C compatible data types;
   they represent C function pointers.

   This behavior can be customized by assigning to special attributes
   of the foreign function object.

   restype

      Assign a ctypes type to specify the result type of the foreign
      function. Use "None" for "void", a function not returning
      anything.

      It is possible to assign a callable Python object that is not a
      ctypes type, in this case the function is assumed to return a C
      "int", and the callable will be called with this integer,
      allowing further processing or error checking.  Using this is
      deprecated, for more flexible post processing or error checking
      use a ctypes data type as "restype" and assign a callable to the
      "errcheck" attribute.

   argtypes

      Assign a tuple of ctypes types to specify the argument types
      that the function accepts.  Functions using the "stdcall"
      calling convention can only be called with the same number of
      arguments as the length of this tuple; functions using the C
      calling convention accept additional, unspecified arguments as
      well.

      When a foreign function is called, each actual argument is
      passed to the "from_param()" class method of the items in the
      "argtypes" tuple, this method allows adapting the actual
      argument to an object that the foreign function accepts.  For
      example, a "c_char_p" item in the "argtypes" tuple will convert
      a string passed as argument into a bytes object using ctypes
      conversion rules.

      New: It is now possible to put items in argtypes which are not
      ctypes types, but each item must have a "from_param()" method
      which returns a value usable as argument (integer, string,
      ctypes instance).  This allows defining adapters that can adapt
      custom objects as function parameters.

   errcheck

      Assign a Python function or another callable to this attribute.
      The callable will be called with three or more arguments:

      callable(result, func, arguments)

         *result* is what the foreign function returns, as specified
         by the "restype" attribute.

         *func* is the foreign function object itself, this allows
         reusing the same callable object to check or post process the
         results of several functions.

         *arguments* is a tuple containing the parameters originally
         passed to the function call, this allows specializing the
         behavior on the arguments used.

      The object that this function returns will be returned from the
      foreign function call, but it can also check the result value
      and raise an exception if the foreign function call failed.

exception ctypes.ArgumentError

   Esta exceção é levantada quando uma chamada de função externa não
   consegue converter um dos argumentos passados.

On Windows, when a foreign function call raises a system exception
(for example, due to an access violation), it will be captured and
replaced with a suitable Python exception. Further, an auditing event
"ctypes.seh_exception" with argument "code" will be raised, allowing
an audit hook to replace the exception with its own.

Some ways to invoke foreign function calls may raise an auditing event
"ctypes.call_function" with arguments "function pointer" and
"arguments".


Function prototypes
-------------------

Foreign functions can also be created by instantiating function
prototypes. Function prototypes are similar to function prototypes in
C; they describe a function (return type, argument types, calling
convention) without defining an implementation.  The factory functions
must be called with the desired result type and the argument types of
the function, and can be used as decorator factories, and as such, be
applied to functions through the "@wrapper" syntax. See Funções
Callbacks for examples.

ctypes.CFUNCTYPE(restype, *argtypes, use_errno=False, use_last_error=False)

   The returned function prototype creates functions that use the
   standard C calling convention.  The function will release the GIL
   during the call.  If *use_errno* is set to true, the ctypes private
   copy of the system "errno" variable is exchanged with the real
   "errno" value before and after the call; *use_last_error* does the
   same for the Windows error code.

ctypes.WINFUNCTYPE(restype, *argtypes, use_errno=False, use_last_error=False)

   Windows only: The returned function prototype creates functions
   that use the "stdcall" calling convention.  The function will
   release the GIL during the call.  *use_errno* and *use_last_error*
   have the same meaning as above.

ctypes.PYFUNCTYPE(restype, *argtypes)

   The returned function prototype creates functions that use the
   Python calling convention.  The function will *not* release the GIL
   during the call.

Function prototypes created by these factory functions can be
instantiated in different ways, depending on the type and number of
the parameters in the call:

   prototype(address)

      Returns a foreign function at the specified address which must
      be an integer.

   prototype(callable)

      Create a C callable function (a callback function) from a Python
      *callable*.

   prototype(func_spec[, paramflags])

      Returns a foreign function exported by a shared library.
      *func_spec* must be a 2-tuple "(name_or_ordinal, library)". The
      first item is the name of the exported function as string, or
      the ordinal of the exported function as small integer.  The
      second item is the shared library instance.

   prototype(vtbl_index, name[, paramflags[, iid]])

      Returns a foreign function that will call a COM method.
      *vtbl_index* is the index into the virtual function table, a
      small non-negative integer. *name* is name of the COM method.
      *iid* is an optional pointer to the interface identifier which
      is used in extended error reporting.

      COM methods use a special calling convention: They require a
      pointer to the COM interface as first argument, in addition to
      those parameters that are specified in the "argtypes" tuple.

   The optional *paramflags* parameter creates foreign function
   wrappers with much more functionality than the features described
   above.

   *paramflags* must be a tuple of the same length as "argtypes".

   Each item in this tuple contains further information about a
   parameter, it must be a tuple containing one, two, or three items.

   The first item is an integer containing a combination of direction
   flags for the parameter:

      1
         Specifies an input parameter to the function.

      2
         Output parameter.  The foreign function fills in a value.

      4
         Input parameter which defaults to the integer zero.

   The optional second item is the parameter name as string.  If this
   is specified, the foreign function can be called with named
   parameters.

   The optional third item is the default value for this parameter.

This example demonstrates how to wrap the Windows "MessageBoxW"
function so that it supports default parameters and named arguments.
The C declaration from the windows header file is this:

   WINUSERAPI int WINAPI
   MessageBoxW(
       HWND hWnd,
       LPCWSTR lpText,
       LPCWSTR lpCaption,
       UINT uType);

Here is the wrapping with "ctypes":

   >>> from ctypes import c_int, WINFUNCTYPE, windll
   >>> from ctypes.wintypes import HWND, LPCWSTR, UINT
   >>> prototype = WINFUNCTYPE(c_int, HWND, LPCWSTR, LPCWSTR, UINT)
   >>> paramflags = (1, "hwnd", 0), (1, "text", "Hi"), (1, "caption", "Hello from ctypes"), (1, "flags", 0)
   >>> MessageBox = prototype(("MessageBoxW", windll.user32), paramflags)

The "MessageBox" foreign function can now be called in these ways:

   >>> MessageBox()
   >>> MessageBox(text="Spam, spam, spam")
   >>> MessageBox(flags=2, text="foo bar")

A second example demonstrates output parameters.  The win32
"GetWindowRect" function retrieves the dimensions of a specified
window by copying them into "RECT" structure that the caller has to
supply.  Here is the C declaration:

   WINUSERAPI BOOL WINAPI
   GetWindowRect(
        HWND hWnd,
        LPRECT lpRect);

Here is the wrapping with "ctypes":

   >>> from ctypes import POINTER, WINFUNCTYPE, windll, WinError
   >>> from ctypes.wintypes import BOOL, HWND, RECT
   >>> prototype = WINFUNCTYPE(BOOL, HWND, POINTER(RECT))
   >>> paramflags = (1, "hwnd"), (2, "lprect")
   >>> GetWindowRect = prototype(("GetWindowRect", windll.user32), paramflags)
   >>>

Functions with output parameters will automatically return the output
parameter value if there is a single one, or a tuple containing the
output parameter values when there are more than one, so the
GetWindowRect function now returns a RECT instance, when called.

Output parameters can be combined with the "errcheck" protocol to do
further output processing and error checking.  The win32
"GetWindowRect" api function returns a "BOOL" to signal success or
failure, so this function could do the error checking, and raises an
exception when the api call failed:

   >>> def errcheck(result, func, args):
   ...     if not result:
   ...         raise WinError()
   ...     return args
   ...
   >>> GetWindowRect.errcheck = errcheck
   >>>

If the "errcheck" function returns the argument tuple it receives
unchanged, "ctypes" continues the normal processing it does on the
output parameters.  If you want to return a tuple of window
coordinates instead of a "RECT" instance, you can retrieve the fields
in the function and return them instead, the normal processing will no
longer take place:

   >>> def errcheck(result, func, args):
   ...     if not result:
   ...         raise WinError()
   ...     rc = args[1]
   ...     return rc.left, rc.top, rc.bottom, rc.right
   ...
   >>> GetWindowRect.errcheck = errcheck
   >>>


Funções utilitárias
-------------------

ctypes.addressof(obj)

   Returns the address of the memory buffer as integer.  *obj* must be
   an instance of a ctypes type.

   Levanta um evento de auditoria "ctypes.addressof" com o argumento
   "obj".

ctypes.alignment(obj_or_type)

   Returns the alignment requirements of a ctypes type. *obj_or_type*
   must be a ctypes type or instance.

ctypes.byref(obj[, offset])

   Returns a light-weight pointer to *obj*, which must be an instance
   of a ctypes type.  *offset* defaults to zero, and must be an
   integer that will be added to the internal pointer value.

   "byref(obj, offset)" corresponds to this C code:

      (((char *)&obj) + offset)

   The returned object can only be used as a foreign function call
   parameter. It behaves similar to "pointer(obj)", but the
   construction is a lot faster.

ctypes.cast(obj, type)

   Esta função é semelhante ao operador cast em C. Retorna uma nova
   instância de *type* que aponta para o mesmo bloco de memória que
   *obj*. *type* deve ser um tipo de ponteiro e *obj* deve ser um
   objeto que pode ser interpretado como um ponteiro.

ctypes.create_string_buffer(init_or_size, size=None)

   This function creates a mutable character buffer. The returned
   object is a ctypes array of "c_char".

   *init_or_size* must be an integer which specifies the size of the
   array, or a bytes object which will be used to initialize the array
   items.

   If a bytes object is specified as first argument, the buffer is
   made one item larger than its length so that the last element in
   the array is a NUL termination character. An integer can be passed
   as second argument which allows specifying the size of the array if
   the length of the bytes should not be used.

   Levanta um evento de auditoria "ctypes.create_string_buffer" com os
   argumentos "init", "size".

ctypes.create_unicode_buffer(init_or_size, size=None)

   This function creates a mutable unicode character buffer. The
   returned object is a ctypes array of "c_wchar".

   *init_or_size* must be an integer which specifies the size of the
   array, or a string which will be used to initialize the array
   items.

   If a string is specified as first argument, the buffer is made one
   item larger than the length of the string so that the last element
   in the array is a NUL termination character. An integer can be
   passed as second argument which allows specifying the size of the
   array if the length of the string should not be used.

   Levanta um evento de auditoria "ctypes.create_unicode_buffer" com
   os argumentos "init", "size".

ctypes.DllCanUnloadNow()

   Windows only: This function is a hook which allows implementing in-
   process COM servers with ctypes.  It is called from the
   DllCanUnloadNow function that the _ctypes extension dll exports.

ctypes.DllGetClassObject()

   Windows only: This function is a hook which allows implementing in-
   process COM servers with ctypes.  It is called from the
   DllGetClassObject function that the "_ctypes" extension dll
   exports.

ctypes.util.find_library(name)

   Try to find a library and return a pathname.  *name* is the library
   name without any prefix like "lib", suffix like ".so", ".dylib" or
   version number (this is the form used for the posix linker option
   "-l").  If no library can be found, returns "None".

   The exact functionality is system dependent.

ctypes.util.find_msvcrt()

   Windows only: return the filename of the VC runtime library used by
   Python, and by the extension modules.  If the name of the library
   cannot be determined, "None" is returned.

   If you need to free memory, for example, allocated by an extension
   module with a call to the "free(void *)", it is important that you
   use the function in the same library that allocated the memory.

ctypes.FormatError([code])

   Windows only: Returns a textual description of the error code
   *code*.  If no error code is specified, the last error code is used
   by calling the Windows api function GetLastError.

ctypes.GetLastError()

   Windows only: Returns the last error code set by Windows in the
   calling thread. This function calls the Windows "GetLastError()"
   function directly, it does not return the ctypes-private copy of
   the error code.

ctypes.get_errno()

   Returns the current value of the ctypes-private copy of the system
   "errno" variable in the calling thread.

   Levanta um evento de auditoria "ctypes.get_errno" sem argumentos.

ctypes.get_last_error()

   Windows only: returns the current value of the ctypes-private copy
   of the system "LastError" variable in the calling thread.

   Levanta um evento de auditoria "ctypes.get_last_error" sem
   argumentos.

ctypes.memmove(dst, src, count)

   Same as the standard C memmove library function: copies *count*
   bytes from *src* to *dst*. *dst* and *src* must be integers or
   ctypes instances that can be converted to pointers.

ctypes.memset(dst, c, count)

   Same as the standard C memset library function: fills the memory
   block at address *dst* with *count* bytes of value *c*. *dst* must
   be an integer specifying an address, or a ctypes instance.

ctypes.POINTER(type)

   This factory function creates and returns a new ctypes pointer
   type. Pointer types are cached and reused internally, so calling
   this function repeatedly is cheap. *type* must be a ctypes type.

ctypes.pointer(obj)

   This function creates a new pointer instance, pointing to *obj*.
   The returned object is of the type "POINTER(type(obj))".

   Nota: se você pretende apenas passar um ponteiro para um objeto em
   uma chamada de função externa, deve usar "byref(obj)", que é muito
   mais rápido.

ctypes.resize(obj, size)

   Esta função redimensiona o buffer de memória interno de *obj*, que
   deve ser uma instância de um tipo ctypes. Não é possível reduzir o
   buffer para menos do que o tamanho nativo do tipo do objeto,
   conforme dado por "sizeof(type(obj))", mas é possível aumentá-lo.

ctypes.set_errno(value)

   Define o valor atual da cópia privada do ctypes da variável do
   sistema "errno" na thread de chamada para *value* e devolve o valor
   anterior.

   Levanta um evento de auditoria "ctypes.set_errno" com o argumento
   "errno".

ctypes.set_last_error(value)

   Windows only: set the current value of the ctypes-private copy of
   the system "LastError" variable in the calling thread to *value*
   and return the previous value.

   Levanta um evento de auditoria "ctypes.set_last_error" com o
   argumento "error".

ctypes.sizeof(obj_or_type)

   Retornar o tamanho em bytes de um tipo ctypes ou buffer de memória
   de instância. Faz o mesmo que o operador C "sizeof".

ctypes.string_at(address, size=- 1)

   This function returns the C string starting at memory address
   *address* as a bytes object. If size is specified, it is used as
   size, otherwise the string is assumed to be zero-terminated.

   Raises an auditing event "ctypes.string_at" with arguments
   "address", "size".

ctypes.WinError(code=None, descr=None)

   Windows only: this function is probably the worst-named thing in
   ctypes. It creates an instance of OSError.  If *code* is not
   specified, "GetLastError" is called to determine the error code. If
   *descr* is not specified, "FormatError()" is called to get a
   textual description of the error.

   Alterado na versão 3.3: An instance of "WindowsError" used to be
   created.

ctypes.wstring_at(address, size=- 1)

   This function returns the wide character string starting at memory
   address *address* as a string.  If *size* is specified, it is used
   as the number of characters of the string, otherwise the string is
   assumed to be zero-terminated.

   Raises an auditing event "ctypes.wstring_at" with arguments
   "address", "size".


Data types
----------

class ctypes._CData

   This non-public class is the common base class of all ctypes data
   types. Among other things, all ctypes type instances contain a
   memory block that hold C compatible data; the address of the memory
   block is returned by the "addressof()" helper function. Another
   instance variable is exposed as "_objects"; this contains other
   Python objects that need to be kept alive in case the memory block
   contains pointers.

   Common methods of ctypes data types, these are all class methods
   (to be exact, they are methods of the *metaclass*):

   from_buffer(source[, offset])

      This method returns a ctypes instance that shares the buffer of
      the *source* object.  The *source* object must support the
      writeable buffer interface.  The optional *offset* parameter
      specifies an offset into the source buffer in bytes; the default
      is zero.  If the source buffer is not large enough a
      "ValueError" is raised.

      Levanta um evento de auditoria "ctypes.cdata/buffer" com os
      argumentos "pointer", "size", "offset".

   from_buffer_copy(source[, offset])

      This method creates a ctypes instance, copying the buffer from
      the *source* object buffer which must be readable.  The optional
      *offset* parameter specifies an offset into the source buffer in
      bytes; the default is zero.  If the source buffer is not large
      enough a "ValueError" is raised.

      Levanta um evento de auditoria "ctypes.cdata/buffer" com os
      argumentos "pointer", "size", "offset".

   from_address(address)

      This method returns a ctypes type instance using the memory
      specified by *address* which must be an integer.

      Este método, e outros que indiretamente chamam este método,
      levantam um evento de auditoria "ctypes.cdata" com o argumento
      "address".

   from_param(obj)

      This method adapts *obj* to a ctypes type.  It is called with
      the actual object used in a foreign function call when the type
      is present in the foreign function's "argtypes" tuple; it must
      return an object that can be used as a function call parameter.

      All ctypes data types have a default implementation of this
      classmethod that normally returns *obj* if that is an instance
      of the type.  Some types accept other objects as well.

   in_dll(library, name)

      This method returns a ctypes type instance exported by a shared
      library. *name* is the name of the symbol that exports the data,
      *library* is the loaded shared library.

   Variáveis de instância comuns dos tipos de dados ctypes:

   _b_base_

      Sometimes ctypes data instances do not own the memory block they
      contain, instead they share part of the memory block of a base
      object.  The "_b_base_" read-only member is the root ctypes
      object that owns the memory block.

   _b_needsfree_

      This read-only variable is true when the ctypes data instance
      has allocated the memory block itself, false otherwise.

   _objects

      This member is either "None" or a dictionary containing Python
      objects that need to be kept alive so that the memory block
      contents is kept valid.  This object is only exposed for
      debugging; never modify the contents of this dictionary.


Tipos de dados fundamentais
---------------------------

class ctypes._SimpleCData

   This non-public class is the base class of all fundamental ctypes
   data types. It is mentioned here because it contains the common
   attributes of the fundamental ctypes data types.  "_SimpleCData" is
   a subclass of "_CData", so it inherits their methods and
   attributes. ctypes data types that are not and do not contain
   pointers can now be pickled.

   Instances have a single attribute:

   value

      This attribute contains the actual value of the instance. For
      integer and pointer types, it is an integer, for character
      types, it is a single character bytes object or string, for
      character pointer types it is a Python bytes object or string.

      When the "value" attribute is retrieved from a ctypes instance,
      usually a new object is returned each time.  "ctypes" does *not*
      implement original object return, always a new object is
      constructed.  The same is true for all other ctypes object
      instances.

Fundamental data types, when returned as foreign function call
results, or, for example, by retrieving structure field members or
array items, are transparently converted to native Python types.  In
other words, if a foreign function has a "restype" of "c_char_p", you
will always receive a Python bytes object, *not* a "c_char_p"
instance.

Subclasses of fundamental data types do *not* inherit this behavior.
So, if a foreign functions "restype" is a subclass of "c_void_p", you
will receive an instance of this subclass from the function call. Of
course, you can get the value of the pointer by accessing the "value"
attribute.

These are the fundamental ctypes data types:

class ctypes.c_byte

   Representa o tipo de dados C "signed char" e interpreta o valor
   como um inteiro pequeno. O construtor aceita um inicializador
   inteiro opcional; não há verificação de overflow.

class ctypes.c_char

   Representa o tipo de dados C "char" e interpreta o valor como um
   único caractere. O construtor aceita um inicializador de string
   opcional; o comprimento da string deve ser exatamente um caractere.

class ctypes.c_char_p

   Representa o tipo de dados C "char*" quando aponta para uma string
   terminada em zero. Para um ponteiro de caractere geral que também
   pode apontar para dados binários, deve-se usar "POINTER(c_char)". O
   construtor aceita um endereço inteiro ou um objeto bytes.

class ctypes.c_double

   Representa o tipo de dados C "double". O construtor aceita um
   inicializador opcional de tipo float.

class ctypes.c_longdouble

   Representa o tipo de dados C "long double". O construtor aceita um
   inicializador opcional de tipo float. Em plataformas onde
   "sizeof(long double) == sizeof(double)", é um alias para
   "c_double".

class ctypes.c_float

   Representa o tipo de dados C "float". O construtor aceita um
   inicializador opcional de tipo float.

class ctypes.c_int

   Represents the C "signed int" datatype.  The constructor accepts an
   optional integer initializer; no overflow checking is done.  On
   platforms where "sizeof(int) == sizeof(long)" it is an alias to
   "c_long".

class ctypes.c_int8

   Represents the C 8-bit "signed int" datatype.  Usually an alias for
   "c_byte".

class ctypes.c_int16

   Represents the C 16-bit "signed int" datatype.  Usually an alias
   for "c_short".

class ctypes.c_int32

   Represents the C 32-bit "signed int" datatype.  Usually an alias
   for "c_int".

class ctypes.c_int64

   Represents the C 64-bit "signed int" datatype.  Usually an alias
   for "c_longlong".

class ctypes.c_long

   Represents the C "signed long" datatype.  The constructor accepts
   an optional integer initializer; no overflow checking is done.

class ctypes.c_longlong

   Represents the C "signed long long" datatype.  The constructor
   accepts an optional integer initializer; no overflow checking is
   done.

class ctypes.c_short

   Represents the C "signed short" datatype.  The constructor accepts
   an optional integer initializer; no overflow checking is done.

class ctypes.c_size_t

   Represents the C "size_t" datatype.

class ctypes.c_ssize_t

   Represents the C "ssize_t" datatype.

   Novo na versão 3.2.

class ctypes.c_ubyte

   Represents the C "unsigned char" datatype, it interprets the value
   as small integer.  The constructor accepts an optional integer
   initializer; no overflow checking is done.

class ctypes.c_uint

   Represents the C "unsigned int" datatype.  The constructor accepts
   an optional integer initializer; no overflow checking is done.  On
   platforms where "sizeof(int) == sizeof(long)" it is an alias for
   "c_ulong".

class ctypes.c_uint8

   Represents the C 8-bit "unsigned int" datatype.  Usually an alias
   for "c_ubyte".

class ctypes.c_uint16

   Represents the C 16-bit "unsigned int" datatype.  Usually an alias
   for "c_ushort".

class ctypes.c_uint32

   Represents the C 32-bit "unsigned int" datatype.  Usually an alias
   for "c_uint".

class ctypes.c_uint64

   Represents the C 64-bit "unsigned int" datatype.  Usually an alias
   for "c_ulonglong".

class ctypes.c_ulong

   Represents the C "unsigned long" datatype.  The constructor accepts
   an optional integer initializer; no overflow checking is done.

class ctypes.c_ulonglong

   Represents the C "unsigned long long" datatype.  The constructor
   accepts an optional integer initializer; no overflow checking is
   done.

class ctypes.c_ushort

   Represents the C "unsigned short" datatype.  The constructor
   accepts an optional integer initializer; no overflow checking is
   done.

class ctypes.c_void_p

   Represents the C "void*" type.  The value is represented as
   integer. The constructor accepts an optional integer initializer.

class ctypes.c_wchar

   Represents the C "wchar_t" datatype, and interprets the value as a
   single character unicode string.  The constructor accepts an
   optional string initializer, the length of the string must be
   exactly one character.

class ctypes.c_wchar_p

   Represents the C "wchar_t*" datatype, which must be a pointer to a
   zero-terminated wide character string.  The constructor accepts an
   integer address, or a string.

class ctypes.c_bool

   Represent the C "bool" datatype (more accurately, "_Bool" from
   C99).  Its value can be "True" or "False", and the constructor
   accepts any object that has a truth value.

class ctypes.HRESULT

   Windows only: Represents a "HRESULT" value, which contains success
   or error information for a function or method call.

class ctypes.py_object

   Representa o tipo de dados C "PyObject*". Chamar isto sem um
   argumento cria um ponteiro "NULL" "PyObject*".

The "ctypes.wintypes" module provides quite some other Windows
specific data types, for example "HWND", "WPARAM", or "DWORD".  Some
useful structures like "MSG" or "RECT" are also defined.


Tipos de dados estruturados
---------------------------

class ctypes.Union(*args, **kw)

   Classe base abstrata para uniões em ordem de bytes nativa.

class ctypes.BigEndianStructure(*args, **kw)

   Classe base abstrata para estruturas em ordem de bytes *big
   endian*.

class ctypes.LittleEndianStructure(*args, **kw)

   Classe base abstrata para estruturas em ordem de bytes *little
   endian*.

Structures with non-native byte order cannot contain pointer type
fields, or any other data types containing pointer type fields.

class ctypes.Structure(*args, **kw)

   Classe base abstrata para estruturas em ordem de bytes *nativa*.

   Os tipos concretos de estruturas e uniões devem ser criados por
   subclasse de um destes tipos e, pelo menos, definir uma variável de
   classe "_fields_". O "ctypes" criará *descritores* que permitem ler
   e escrever os campos por meio de acessos diretos aos respectivos
   atributos. Estes são eles

   _fields_

      Uma sequência que define os campos da estrutura. Os itens devem
      ser tuplas com 2 ou 3 elementos. O primeiro item é o nome do
      campo; o segundo item especifica o tipo do campo, que pode ser
      qualquer tipo de dados ctypes.

      Para campos de tipo inteiro como "c_int", pode ser fornecido um
      terceiro item opcional. Deve ser um inteiro positivo pequeno que
      define a largura em bits do campo.

      Os nomes dos campos devem ser únicos em uma estrutura ou união.
      Isto não é verificado, apenas um campo pode ser acessado quando
      os nomes são repetidos.

      É possível definir a variável de classe "_fields_" *depois* da
      instrução de classe que define a subclasse de Structure, o que
      permite criar tipos de dados que referenciam diretamente ou
      indiretamente a si mesmos:

         class List(Structure):
             pass
         List._fields_ = [("pnext", POINTER(List)),
                          ...
                         ]

      The "_fields_" class variable must, however, be defined before
      the type is first used (an instance is created, "sizeof()" is
      called on it, and so on).  Later assignments to the "_fields_"
      class variable will raise an AttributeError.

      It is possible to define sub-subclasses of structure types, they
      inherit the fields of the base class plus the "_fields_" defined
      in the sub-subclass, if any.

   _pack_

      An optional small integer that allows overriding the alignment
      of structure fields in the instance.  "_pack_" must already be
      defined when "_fields_" is assigned, otherwise it will have no
      effect.

   _anonymous_

      An optional sequence that lists the names of unnamed (anonymous)
      fields. "_anonymous_" must be already defined when "_fields_" is
      assigned, otherwise it will have no effect.

      The fields listed in this variable must be structure or union
      type fields. "ctypes" will create descriptors in the structure
      type that allows accessing the nested fields directly, without
      the need to create the structure or union field.

      Here is an example type (Windows):

         class _U(Union):
             _fields_ = [("lptdesc", POINTER(TYPEDESC)),
                         ("lpadesc", POINTER(ARRAYDESC)),
                         ("hreftype", HREFTYPE)]

         class TYPEDESC(Structure):
             _anonymous_ = ("u",)
             _fields_ = [("u", _U),
                         ("vt", VARTYPE)]

      The "TYPEDESC" structure describes a COM data type, the "vt"
      field specifies which one of the union fields is valid.  Since
      the "u" field is defined as anonymous field, it is now possible
      to access the members directly off the TYPEDESC instance.
      "td.lptdesc" and "td.u.lptdesc" are equivalent, but the former
      is faster since it does not need to create a temporary union
      instance:

         td = TYPEDESC()
         td.vt = VT_PTR
         td.lptdesc = POINTER(some_type)
         td.u.lptdesc = POINTER(some_type)

   It is possible to define sub-subclasses of structures, they inherit
   the fields of the base class.  If the subclass definition has a
   separate "_fields_" variable, the fields specified in this are
   appended to the fields of the base class.

   Structure and union constructors accept both positional and keyword
   arguments.  Positional arguments are used to initialize member
   fields in the same order as they are appear in "_fields_".  Keyword
   arguments in the constructor are interpreted as attribute
   assignments, so they will initialize "_fields_" with the same name,
   or create new attributes for names not present in "_fields_".


Arrays and pointers
-------------------

class ctypes.Array(*args)

   Abstract base class for arrays.

   The recommended way to create concrete array types is by
   multiplying any "ctypes" data type with a non-negative integer.
   Alternatively, you can subclass this type and define "_length_" and
   "_type_" class variables. Array elements can be read and written
   using standard subscript and slice accesses; for slice reads, the
   resulting object is *not* itself an "Array".

   _length_

      A positive integer specifying the number of elements in the
      array. Out-of-range subscripts result in an "IndexError". Will
      be returned by "len()".

   _type_

      Specifies the type of each element in the array.

   Array subclass constructors accept positional arguments, used to
   initialize the elements in order.

class ctypes._Pointer

   Private, abstract base class for pointers.

   Concrete pointer types are created by calling "POINTER()" with the
   type that will be pointed to; this is done automatically by
   "pointer()".

   If a pointer points to an array, its elements can be read and
   written using standard subscript and slice accesses.  Pointer
   objects have no size, so "len()" will raise "TypeError".  Negative
   subscripts will read from the memory *before* the pointer (as in
   C), and out-of-range subscripts will probably crash with an access
   violation (if you're lucky).

   _type_

      Specifies the type pointed to.

   contents

      Returns the object to which to pointer points.  Assigning to
      this attribute changes the pointer to point to the assigned
      object.
