tempnam − create a name for a temporary file


#include <stdio.h>

char *tempnam(const char *dir, const char *pfx);


The tempnam() function returns a pointer to a string that is a valid filename, and such that a file with this name did not exist when tempnam() checked. The filename suffix of the pathname generated will start with pfx in case pfx is a non-NULL string of at most five bytes. The directory prefix part of the pathname generated is required to be ’appropriate’ (often that at least implies writable). Attempts to find an appropriate directory go through the following steps: (i) In case the environment variable TMPDIR exists and contains the name of an appropriate directory, that is used. (ii) Otherwise, if the dir argument is non-NULL and appropriate, it is used. (iii) Otherwise, P_tmpdir (as defined in <stdio.h>) is used when appropriate. (iv) Finally an implementation-defined directory may be used.


The tempnam() function returns a pointer to a unique temporary filename, or NULL if a unique name cannot be generated.



Allocation of storage failed.


SUSv2 does not mention the use of TMPDIR; glibc will use it only when the program is not suid. SVID2 specifies that the directory used under (iv) is /tmp. SVID2 specifies that the string returned by tempnam() was allocated using malloc(3) and hence can be freed by free(3).

The tempnam() function generates a different string each time it is called, up to TMP_MAX (defined in <stdio.h>) times. If it is called more than TMP_MAX times, the behaviour is implementation defined.

In case the pfx argument has length larger than five, glibc will use the first five bytes. Upon failure to find a unique name, glibc will return EEXIST.


The precise meaning of ’appropriate’ is undefined; it is unspecified how accessibility of a directory is determined. Never use this function. Use mkstemp(3) instead.


SVID 2, BSD 4.3


mktemp(3), mkstemp(3), tmpfile(3), tmpnam(3)