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\section{\module{msvcrt} --
Useful routines from the MS VC++ runtime}
\declaremodule{builtin}{msvcrt}
\platform{Windows}
\modulesynopsis{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
\refmodule{getpass} module uses this in the implementation of the
\function{getpass()} function.
Further documentation on these functions can be found in the Platform
API documentation.
\subsection{File Operations \label{msvcrt-files}}
\begin{funcdesc}{locking}{fd, mode, nbytes}
Lock part of a file based on file descriptor \var{fd} from the C
runtime. Raises \exception{IOError} on failure. The locked region
of the file extends from the current file position for \var{nbytes}
bytes, and may continue beyond the end of the file. \var{mode} must
be one of the \constant{LK_\var{*}} 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.
\end{funcdesc}
\begin{datadesc}{LK_LOCK}
\dataline{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, \exception{IOError} is
raised.
\end{datadesc}
\begin{datadesc}{LK_NBLCK}
\dataline{LK_NBRLCK}
Locks the specified bytes. If the bytes cannot be locked,
\exception{IOError} is raised.
\end{datadesc}
\begin{datadesc}{LK_UNLCK}
Unlocks the specified bytes, which must have been previously locked.
\end{datadesc}
\begin{funcdesc}{setmode}{fd, flags}
Set the line-end translation mode for the file descriptor \var{fd}.
To set it to text mode, \var{flags} should be \constant{os.O_TEXT};
for binary, it should be \constant{os.O_BINARY}.
\end{funcdesc}
\begin{funcdesc}{open_osfhandle}{handle, flags}
Create a C runtime file descriptor from the file handle
\var{handle}. The \var{flags} parameter should be a bit-wise OR of
\constant{os.O_APPEND}, \constant{os.O_RDONLY}, and
\constant{os.O_TEXT}. The returned file descriptor may be used as a
parameter to \function{os.fdopen()} to create a file object.
\end{funcdesc}
\begin{funcdesc}{get_osfhandle}{fd}
Return the file handle for the file descriptor \var{fd}. Raises
\exception{IOError} if \var{fd} is not recognized.
\end{funcdesc}
\subsection{Console I/O \label{msvcrt-console}}
\begin{funcdesc}{kbhit}{}
Return true if a keypress is waiting to be read.
\end{funcdesc}
\begin{funcdesc}{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
\code{'\e000'} or \code{'\e xe0'}; the next call will return the
keycode. The \kbd{Control-C} keypress cannot be read with this
function.
\end{funcdesc}
\begin{funcdesc}{getche}{}
Similar to \function{getch()}, but the keypress will be echoed if it
represents a printable character.
\end{funcdesc}
\begin{funcdesc}{putch}{char}
Print the character \var{char} to the console without buffering.
\end{funcdesc}
\begin{funcdesc}{ungetch}{char}
Cause the character \var{char} to be ``pushed back'' into the
console buffer; it will be the next character read by
\function{getch()} or \function{getche()}.
\end{funcdesc}
\subsection{Other Functions \label{msvcrt-other}}
\begin{funcdesc}{heapmin}{}
Force the \cfunction{malloc()} heap to clean itself up and return
unused blocks to the operating system. This only works on Windows
NT. On failure, this raises \exception{IOError}.
\end{funcdesc}
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