TMPNAM(3S) (C Programming Language Utilities) TMPNAM(3S)
NAME
tmpnam, tempnam - create a name for a temporary file
SYNOPSIS
#include <stdio.h>
char *tmpnam (s)
char *s;
char *tempnam (dir, pfx)
char *dir, *pfx;
DESCRIPTION
These functions generate file names that can safely be used
for a temporary file.
tmpnam always generates a file name using the path-prefix
defined as Ptmpdir 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
Ltmpnam bytes, where Ltmpnam 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 that is not a name for an
appropriate directory, the path-prefix defined as Ptmpdir
in the <stdio.h> header file is used. If that directory is
not accessible, /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 directory.
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
Page 1 May 1989
TMPNAM(3S) (C Programming Language Utilities) TMPNAM(3S)
point to a string of up to five characters to be used as the
first few characters of the temporary-file name.
Tempnam uses malloc(3C) 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(3C)]. If tempnam cannot return the
expected result for any reason, i.e. malloc(3C) failed, or
none of the above mentioned attempts to find an appropriate
directory was successful, a NULL pointer will be returned.
NOTES
These functions generate a different file name each time
they are called.
Files created using these functions and either fopen(3S) 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 use unlink(2) to
remove the file when its use is ended.
SEE ALSO
creat(2), unlink(2), fopen(3S), malloc(3C), mktemp(3C),
tmpfile(3S).
CAVEATS
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 to render duplication by other means
unlikely.
Page 2 May 1989