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: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.
.. _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:`IOError` 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:`IOError` is raised.
.. data:: LK_NBLCK
LK_NBRLCK
Locks the specified bytes. If the bytes cannot be locked, :exc:`IOError` 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 bit-wise 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:`IOError` 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. 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:: getche()
Similar to :func:`getch`, but the keypress will be echoed if it represents a
printable character.
.. function:: putch(char)
Print the character *char* to the console without buffering.
.. function:: ungetch(char)
Cause the character *char* to be "pushed back" into the console buffer; it will
be the next character read by :func:`getch` or :func:`getche`.
.. _msvcrt-other:
Other Functions
---------------
.. function:: heapmin()
Force the :cfunc:`malloc` heap to clean itself up and return unused blocks to
the operating system. This only works on Windows NT. On failure, this raises
:exc:`IOError`.
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