Make a unique temporary filename


#include <stdlib.h>

char* mktemp( 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 mktemp() 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 mktemp() can return depends on the number of Xs provided; if you specify six Xs, mktemp() tests roughly 266 combinations.

The mkstemp() function (unlike this function) 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.


A pointer to the template, or NULL on failure (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 stat().


POSIX 1003.1 XSI

Cancellation point No
Interrupt handler No
Signal handler Yes
Thread Yes


In general, avoid using mktemp(), because a hostile process can exploit a race condition in the time between the generation of a temporary filename by mktemp() and the invoker's use of the temporary name. Use mkstemp() instead.

This function can create only 26 unique file names per thread for each unique template.