字串轉換與格式化

數字轉換函數和被格式化的字串輸出。

int PyOS_snprintf(char *str, size_t size, const char *format, ...)

Output not more than size bytes to str according to the format string format and the extra arguments. See the Unix man page snprintf(2).

int PyOS_vsnprintf(char *str, size_t size, const char *format, va_list va)

Output not more than size bytes to str according to the format string format and the variable argument list va. Unix man page vsnprintf(2).

PyOS_snprintf() and PyOS_vsnprintf() wrap the Standard C library functions snprintf() and vsnprintf(). Their purpose is to guarantee consistent behavior in corner cases, which the Standard C functions do not.

The wrappers ensure that str*[*size-1] is always '\0' upon return. They never write more than size bytes (including the trailing '\0') into str. Both functions require that str != NULL, size > 0 and format != NULL.

如果平台没有 vsnprintf() 而且缓冲区大小需要避免截断超出 size 512 字节以上，Python 会以一个 Py_FatalError() 来中止。

當回傳值 (rv) 給這些函數應該被編譯如下：

• When 0 <= rv < size, the output conversion was successful and rv characters were written to str (excluding the trailing '\0' byte at str*[*rv]).

• When rv >= size, the output conversion was truncated and a buffer with rv + 1 bytes would have been needed to succeed. str*[*size-1] is '\0' in this case.

• When rv < 0, "something bad happened." str*[*size-1] is '\0' in this case too, but the rest of str is undefined. The exact cause of the error depends on the underlying platform.

The following functions provide locale-independent string to number conversions.

double PyOS_string_to_double(const char *s, char **endptr, PyObject *overflow_exception)

Convert a string s to a double, raising a Python exception on failure. The set of accepted strings corresponds to the set of strings accepted by Python's float() constructor, except that s must not have leading or trailing whitespace. The conversion is independent of the current locale.

If endptr is NULL, convert the whole string. Raise ValueError and return -1.0 if the string is not a valid representation of a floating-point number.

If endptr is not NULL, convert as much of the string as possible and set *endptr to point to the first unconverted character. If no initial segment of the string is the valid representation of a floating-point number, set *endptr to point to the beginning of the string, raise ValueError, and return -1.0.

If s represents a value that is too large to store in a float (for example, "1e500" is such a string on many platforms) then if overflow_exception is NULL return Py_HUGE_VAL (with an appropriate sign) and don't set any exception. Otherwise, overflow_exception must point to a Python exception object; raise that exception and return -1.0. In both cases, set *endptr to point to the first character after the converted value.

If any other error occurs during the conversion (for example an out-of-memory error), set the appropriate Python exception and return -1.0.

3.1 版新加入.

char* PyOS_double_to_string(double val, char format_code, int precision, int flags, int *ptype)

Convert a double val to a string using supplied format_code, precision, and flags.

format_code must be one of 'e', 'E', 'f', 'F', 'g', 'G' or 'r'. For 'r', the supplied precision must be 0 and is ignored. The 'r' format code specifies the standard repr() format.

flags 可以为零或者其他值 Py_DTSF_SIGN, Py_DTSF_ADD_DOT_0 或 Py_DTSF_ALT 或其组合：

• Py_DTSF_SIGN 表示总是在返回的字符串前附加一个符号字符，即使 val 为非负数。

• Py_DTSF_ADD_DOT_0 表示确保返回的字符串看起来不像是一个整数。

• Py_DTSF_ALT 表示应用 "替代的" 格式化规则。 相关细节请参阅 PyOS_snprintf() '#' 定义文档。

如果 ptype 不为 NULL，则它指向的值将被设为 Py_DTST_FINITE, Py_DTST_INFINITE 或 Py_DTST_NAN 中的一个，分别表示 val 是一个有限数字、无限数字或非数字。

返回值是一个指向包含转换后字符串的 buffer 的指针，如果转换失败则为 NULL。 调用方要负责调用 PyMem_Free() 来释放返回的字符串。

3.1 版新加入.

int PyOS_stricmp(const char *s1, const char *s2)

Case insensitive comparison of strings. The function works almost identically to strcmp() except that it ignores the case.

int PyOS_strnicmp(const char *s1, const char *s2, Py_ssize_t  size)

Case insensitive comparison of strings. The function works almost identically to strncmp() except that it ignores the case.