TMPNAM(3C) Standard C Library Functions TMPNAM(3C)

tmpnam, tmpnam_r, tempnam - create a name for a temporary file

#include <stdio.h>
char *tmpnam(char *s);

char *tmpnam_r(char *s);

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

These functions generate file names that can be used safely for a temporary file.


The tmpnam() function always generates a file name using the path prefix defined as P_tmpdir in the <stdio.h> header. On Solaris systems, the default value for P_tmpdir is /var/tmp. If s is NULL, tmpnam() leaves its result in a thread-specific data area and returns a pointer to that area. The next call to tmpnam() by the same thread will destroy the contents of the area. If s is not NULL, it is assumed to be the address of an array of at least L_tmpnam bytes, where L_tmpnam is a constant defined through inclusion of <stdio.h>. The tmpnam() function places its result in that array and returns s.


The tmpnam_r() function has the same functionality as tmpnam() except that if s is a null pointer, the function returns NULL.


The tempnam() function allows the user to control the choice of a directory. The argument dir points to the name of the directory in which the file is to be created. If dir is NULL or points to a string that is not a name for an appropriate directory, the path prefix defined as P_tmpdir in the <stdio.h> header is used. If that directory is not accessible, /tmp is used. If, however, the TMPDIR environment variable is set in the user's environment, its value is used as the temporary-file directory.

Many applications prefer that temporary files have certain initial character sequences in their names. The pfx argument may be NULL or point to a string of up to five characters to be used as the initial characters of the temporary-file name.

Upon successful completion, tempnam() uses malloc(3C) to allocate space for a string, puts the generated pathname in that space, and returns a pointer to it. The pointer is suitable for use in a subsequent call to free(). If tempnam() cannot return the expected result for any reason (for example, malloc() failed), or if none of the above-mentioned attempts to find an appropriate directory was successful, a null pointer is returned and errno is set to indicate the error.

The tempnam() function will fail if:


Insufficient storage space is available.

These functions generate a different file name each time they are called.

Files created using these functions and either fopen(3C) or creat(2) are temporary only in the sense that they reside in a directory intended for temporary use, and their names are unique. It is the user's responsibility to remove the file when its use is ended.

If called more than TMP_MAX (defined in <stdio.h>) times in a single process, these functions start recycling previously used names.

Between the time a file name is created and the file is opened, it is possible for some other process to create a file with the same name. This can never happen if that other process is using these functions or mktemp(3C) and the file names are chosen to render duplication by other means unlikely.

The tmpnam() function is safe to use in multithreaded applications because it employs thread-specific data if it is passed a NULL pointer. However, its use is discouraged. The tempnam() function is safe in multithreaded applications and should be used instead.

When compiling multithreaded applications, the _REENTRANT flag must be defined on the compile line. This flag should be used only with multithreaded applications.

See attributes(7) for descriptions of the following attributes:

Interface Stability tmpnam() and tempnam() are Standard.
MT-Level Safe

creat(2), unlink(2), fopen(3C), free(3C), malloc(3C), mkstemp(3C), mktemp(3C), tmpfile(3C), attributes(7), standards(7)

May 18, 2004 OmniOS