tmpnam, tmpnam_r, tempnam - create a name for a temporary file
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 tem‐
The tmpnam() function always generates a file name using the path pre‐
fix 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
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
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
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 mul‐
tithreaded 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 multi‐
See attributes(5) for descriptions of the following attributes:
│ ATTRIBUTE TYPE │ ATTRIBUTE VALUE │
│Interface Stability │ tmpnam() and tempnam() are Standard. │
│MT-Level │ Safe │
SEE ALSOcreat(2), unlink(2), fopen(3C), free(3C), malloc(3C), mktemp(3C),
mkstemp(3C), tmpfile(3C), attributes(5), standards(5)
May 18, 2004 TMPNAM(3C)