tmpnam - Man Page

create a name for a temporary file


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.


#include <stdio.h>

char *tmpnam(char *s);


The functionality described on this reference page is aligned with the ISO C standard. Any conflict between the requirements described here and the ISO C standard is unintentional. This volume of POSIX.1-2017 defers to the ISO C standard.

The tmpnam() function shall generate a string that is a valid pathname that does not name an existing file. The function is potentially capable of generating {TMP_MAX} different strings, but any or all of them may already be in use by existing files and thus not be suitable return values.

The tmpnam() function generates a different string each time it is called from the same process, up to {TMP_MAX} times. If it is called more than {TMP_MAX} times, the behavior is implementation-defined.

The implementation shall behave as if no function defined in this volume of POSIX.1-2017, except tempnam(), calls tmpnam().

The tmpnam() function need not be thread-safe if called with a NULL parameter.

Return Value

Upon successful completion, tmpnam() shall return a pointer to a string. If no suitable string can be generated, the tmpnam() function shall return a null pointer.

If the argument s is a null pointer, tmpnam() shall leave its result in an internal static object and return a pointer to that object. Subsequent calls to tmpnam() may modify the same object. If the argument s is not a null pointer, it is presumed to point to an array of at least L_tmpnam chars; tmpnam() shall write its result in that array and shall return the argument as its value.


No errors are defined.

The following sections are informative.


Generating a Pathname

The following example generates a unique pathname and stores it in the array pointed to by ptr.

#include <stdio.h>
char pathname[L_tmpnam+1];
char *ptr;

ptr = tmpnam(pathname);

Application Usage

This function only creates pathnames. It is the application's responsibility to create and remove the files.

Between the time a pathname is created and the file is opened, it is possible for some other process to create a file with the same name. Applications may find tmpfile() more useful.

Applications should use the tmpfile(), mkstemp(), or mkdtemp() functions instead of the obsolescent tmpnam() function.



Future Directions

The tmpnam() function may be removed in a future version.

See Also

fopen(), open(), mkdtemp(), tempnam(), tmpfile(), unlink()

The Base Definitions volume of POSIX.1-2017, <stdio.h>

Referenced By

mkdtemp(3p), stdio.h(0p), tempnam(3p), tmpfile(3p).

2017 IEEE/The Open Group POSIX Programmer's Manual