:mod:`msvcrt` --- Useful routines from the MS VC++ runtime
==========================================================

.. module:: msvcrt
   :platform: Windows
   :synopsis: Miscellaneous useful routines from the MS VC++ runtime.

.. sectionauthor:: Fred L. Drake, Jr. <fdrake@acm.org>

--------------

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 :mod:`getpass` module uses
this in the implementation of the :func:`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.

.. versionchanged:: 3.3
   Operations in this module now raise :exc:`OSError` where :exc:`IOError`
   was raised.


.. _msvcrt-files:

File Operations
---------------


.. function:: locking(fd, mode, nbytes)

   Lock part of a file based on file descriptor *fd* from the C runtime.  Raises
   :exc:`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 :const:`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.


.. data:: LK_LOCK
          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, :exc:`OSError` is raised.


.. data:: LK_NBLCK
          LK_NBRLCK

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


.. data:: LK_UNLCK

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


.. function:: setmode(fd, flags)

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


.. function:: open_osfhandle(handle, flags)

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


.. function:: get_osfhandle(fd)

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


.. _msvcrt-console:

Console I/O
-----------


.. function:: kbhit()

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


.. function:: 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 :kbd:`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 :kbd:`Control-C` keypress cannot be read with this function.


.. function:: getwch()

   Wide char variant of :func:`getch`, returning a Unicode value.


.. function:: getche()

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


.. function:: getwche()

   Wide char variant of :func:`getche`, returning a Unicode value.


.. function:: putch(char)

   Print the byte string *char* to the console without buffering.


.. function:: putwch(unicode_char)

   Wide char variant of :func:`putch`, accepting a Unicode value.


.. function:: ungetch(char)

   Cause the byte string *char* to be "pushed back" into the console buffer;
   it will be the next character read by :func:`getch` or :func:`getche`.


.. function:: ungetwch(unicode_char)

   Wide char variant of :func:`ungetch`, accepting a Unicode value.


.. _msvcrt-other:

Other Functions
---------------


.. function:: heapmin()

   Force the :c:func:`malloc` heap to clean itself up and return unused blocks to
   the operating system.  On failure, this raises :exc:`OSError`.