mkstemp (3p) - Linux Man Pages

mkstemp: make a unique filename


This manual page is part of the POSIX Programmer's Manual. The Linux implementation of this interface may differ (consult the corresponding Linux manual page for details of Linux behavior), or the interface may not be implemented on Linux.


mkstemp - make a unique filename


#include <stdlib.h>

int mkstemp(char *template);


The mkstemp() function shall replace the contents of the string pointed to by template by a unique filename, and return a file descriptor for the file open for reading and writing. The function thus prevents any possible race condition between testing whether the file exists and opening it for use. The string in template should look like a filename with six trailing 'X' s; mkstemp() replaces each 'X' with a character from the portable filename character set. The characters are chosen such that the resulting name does not duplicate the name of an existing file at the time of a call to mkstemp().


Upon successful completion, mkstemp() shall return an open file descriptor. Otherwise, -1 shall be returned if no suitable file could be created.


No errors are defined.

The following sections are informative.


Generating a Filename

The following example creates a file with a 10-character name beginning with the characters "file" and opens the file for reading and writing. The value returned as the value of fd is a file descriptor that identifies the file.

#include <stdlib.h>
char template[] = "/tmp/fileXXXXXX";
int fd;

fd = mkstemp(template);


It is possible to run out of letters.

The mkstemp() function need not check to determine whether the filename part of template exceeds the maximum allowable filename length.






Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of Electrical and Electronics Engineers, Inc and The Open Group. In the event of any discrepancy between this version and the original IEEE and The Open Group Standard, the original IEEE and The Open Group Standard is the referee document. The original Standard can be obtained online at .


getpid(), open(), tmpfile(), tmpnam(), the Base Definitions volume of IEEE Std 1003.1-2001, <stdlib.h>