tmpnam, tempnam - create a name for a temporary file
char *tmpnam (s)
char *tempnam (dir, pfx)
char *dir, *pfx;
These functions generate file names that can safely be used for a tem-
tmpnam() always generates a file name using the path-prefix defined as
P_tmpdir in the <<stdio.h>> header file. If s is NULL, tmpnam() leaves
its result in an internal static area and returns a pointer to that
area. The next call to tmpnam() 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 in
<<stdio.h>>; tmpnam() places its result in that array and returns s.
tempnam() 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 which is not a
name for an appropriate directory, the path-prefix defined as P_tmpdir
in the <<stdio.h>> header file is used. If that directory is not acces-
sible, /tmp will be used as a last resort. This entire sequence can be
up-staged by providing an environment variable TMPDIR in the user's
environment, whose value is the name of the desired temporary-file
Many applications prefer their temporary files to have certain favorite
initial letter sequences in their names. Use the pfx argument for
this. This argument may be NULL or point to a string of up to five
characters to be used as the first few characters of the temporary-file
tempnam() uses malloc() to get space for the constructed file name, and
returns a pointer to this area. Thus, any pointer value returned from
tempnam() may serve as an argument to free (see malloc(3V)). If temp-
nam() cannot return the expected result for any reason, that is, mal-
loc() failed, or none of the above mentioned attempts to find an appro-
priate directory was successful, a NULL pointer will be returned.
These functions generate a different file name each time they are
Files created using these functions and either fopen() or creat() 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 use unlink(2V) to remove the file when its use is
creat(2V), unlink(2V), fopen(3V), malloc(3V), mktemp(3), tmpfile(3S)
If called more than 17,576 times in a single process, these functions
will 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(), and the file names are chosen so as to render duplication by
other means unlikely.
1 February 1988 TMPNAM(3S)