Make a unique temporary filename, and open the file


#include <stdlib.h>

int mkstemp( char* template );


A template for the filename that you want to use. This template can be any file name with some number of Xs appended to it, for example /tmp/temp.XXXX.



Use the -l c option to qcc to link against this library. This library is usually included automatically.


The mkstemp() function takes the given file name template and overwrites a portion of it to create a filename. This file name is unique and suitable for use by the application. The trailing Xs are replaced with the current process number and/or a unique letter combination. The number of unique file names mkstemp() can return depends on the number of Xs provided; if you specify six Xs, mkstemp() tests roughly 266 combinations.

The mkstemp() function (unlike mktemp()) creates the template file, mode 0600 (i.e., read-write for the owner), returning a file descriptor opened for reading and writing. This avoids the race between testing for a file's existence and opening it for use.


The file descriptor of the temporary file, or -1 if no suitable file could be created (errno is set).


The pathname portion of the template isn't an existing directory.

This function may also set errno to any value specified by open() and stat().


POSIX 1003.1

Cancellation point Yes
Interrupt handler No
Signal handler Yes
Thread Yes


It's possible to run out of letters. The mkstemp() function doesn't check to determine whether the file name part of template exceeds the maximum allowable filename length.

For portability with X/Open standards prior to XPG4v2, use tmpfile() instead.