# `msvcrt` — Useful routines from the MS VC++ runtime

These functions provide access to some useful capabilities on Windows platforms. Some higher-level modules use these functions to build the Windows implementations of their services. For example, the `getpass` module uses this in the implementation of the `getpass()` function.

Further documentation on these functions can be found in the Platform API documentation.

The module implements both the normal and wide char variants of the console I/O api. The normal API deals only with ASCII characters and is of limited use for internationalized applications. The wide char API should be used where ever possible.

Distinto en la versión 3.3: Operations in this module now raise `OSError` where `IOError` was raised.

## File Operations

`msvcrt.``locking`(fd, mode, nbytes)

  Lock part of a file based on file descriptor fd from the C runtime. Raises `OSError` on failure. The locked region of the file extends from the current file position for nbytes bytes, and may continue beyond the end of the file. mode must be one of the `LK_*` constants listed below. Multiple regions in a file may be locked at the same time, but may not overlap. Adjacent regions are not merged; they must be unlocked individually.

`msvcrt.``LK_LOCK`
`msvcrt.``LK_RLCK`

  Locks the specified bytes. If the bytes cannot be locked, the program immediately tries again after 1 second. If, after 10 attempts, the bytes cannot be locked, `OSError` is raised.

`msvcrt.``LK_NBLCK`
`msvcrt.``LK_NBRLCK`

  Locks the specified bytes. If the bytes cannot be locked, `OSError` is raised.

`msvcrt.``LK_UNLCK`

  Unlocks the specified bytes, which must have been previously locked.

`msvcrt.``setmode`(fd, flags)

  Set the line-end translation mode for the file descriptor fd. To set it to text mode, flags should be `os.O_TEXT`; for binary, it should be `os.O_BINARY`.

`msvcrt.``open_osfhandle`(handle, flags)

  Create a C runtime file descriptor from the file handle handle. The flags parameter should be a bitwise OR of `os.O_APPEND`, `os.O_RDONLY`, and `os.O_TEXT`. The returned file descriptor may be used as a parameter to `os.fdopen()` to create a file object.

`msvcrt.``get_osfhandle`(fd)

  Return the file handle for the file descriptor fd. Raises `OSError` if fd is not recognized.

## Console I/O

`msvcrt.``kbhit`()

  Return `True` if a keypress is waiting to be read.

`msvcrt.``getch`()

  Read a keypress and return the resulting character as a byte string. Nothing is echoed to the console. This call will block if a keypress is not already available, but will not wait for `Enter` to be pressed. If the pressed key was a special function key, this will return `'\000'` or `'\xe0'`; the next call will return the keycode. The `Control-C` keypress cannot be read with this function.

`msvcrt.``getwch`()

  Wide char variant of `getch()`, returning a Unicode value.

`msvcrt.``getche`()

  Similar to `getch()`, but the keypress will be echoed if it represents a printable character.

`msvcrt.``getwche`()

  Wide char variant of `getche()`, returning a Unicode value.

`msvcrt.``putch`(char)

  Print the byte string char to the console without buffering.

`msvcrt.``putwch`(unicode_char)

  Wide char variant of `putch()`, accepting a Unicode value.

`msvcrt.``ungetch`(char)

  Cause the byte string char to be «pushed back» into the console buffer; it will be the next character read by `getch()` or `getche()`.

`msvcrt.``ungetwch`(unicode_char)

  Wide char variant of `ungetch()`, accepting a Unicode value.

## Other Functions

`msvcrt.``heapmin`()

  Force the `malloc()` heap to clean itself up and return unused blocks to the operating system. On failure, this raises `OSError`.