tmpnam(3) — Linux manual page


TMPNAM(3)               Linux Programmer's Manual              TMPNAM(3)

NAME         top

       tmpnam, tmpnam_r - create a name for a temporary file

SYNOPSIS         top

       #include <stdio.h>

       char *tmpnam(char *s);
       char *tmpnam_r(char *s);

   Feature Test Macro Requirements for glibc (see

           Since glibc 2.19:
           Up to and including glibc 2.19:
               _BSD_SOURCE || _SVID_SOURCE

DESCRIPTION         top

       Note: avoid using these functions; use mkstemp(3) or tmpfile(3)

       The tmpnam() function returns a pointer to a string that is a
       valid filename, and such that a file with this name did not exist
       at some point in time, so that naive programmers may think it a
       suitable name for a temporary file.  If the argument s is NULL,
       this name is generated in an internal static buffer and may be
       overwritten by the next call to tmpnam().  If s is not NULL, the
       name is copied to the character array (of length at least
       L_tmpnam) pointed to by s and the value s is returned in case of

       The created pathname has a directory prefix P_tmpdir.  (Both
       L_tmpnam and P_tmpdir are defined in <stdio.h>, just like the
       TMP_MAX mentioned below.)

       The tmpnam_r() function performs the same task as tmpnam(), but
       returns NULL (to indicate an error) if s is NULL.

RETURN VALUE         top

       These functions return a pointer to a unique temporary filename,
       or NULL if a unique name cannot be generated.

ERRORS         top

       No errors are defined.

ATTRIBUTES         top

       For an explanation of the terms used in this section, see

       │Interface            Attribute     Value                    │
       │tmpnam()             │ Thread safety │ MT-Unsafe race:tmpnam/!s │
       │tmpnam_r()           │ Thread safety │ MT-Safe                  │

CONFORMING TO         top

       tmpnam(): SVr4, 4.3BSD, C89, C99, POSIX.1-2001.  POSIX.1-2008
       marks tmpnam() as obsolete.

       tmpnam_r() is a nonstandard extension that is also available on a
       few other systems.

NOTES         top

       The tmpnam() function generates a different string each time it
       is called, up to TMP_MAX times.  If it is called more than
       TMP_MAX times, the behavior is implementation defined.

       Although these functions generate names that are difficult to
       guess, it is nevertheless possible that between the time that the
       pathname is returned and the time that the program opens it,
       another program might create that pathname using open(2), or
       create it as a symbolic link.  This can lead to security holes.
       To avoid such possibilities, use the open(2) O_EXCL flag to open
       the pathname.  Or better yet, use mkstemp(3) or tmpfile(3).

       Portable applications that use threads cannot call tmpnam() with
       a NULL argument if either _POSIX_THREADS or

BUGS         top

       Never use these functions.  Use mkstemp(3) or tmpfile(3) instead.

SEE ALSO         top

       mkstemp(3), mktemp(3), tempnam(3), tmpfile(3)

COLOPHON         top

       This page is part of release 5.13 of the Linux man-pages project.
       A description of the project, information about reporting bugs,
       and the latest version of this page, can be found at

                               2021-03-22                      TMPNAM(3)

Pages that refer to this page: getpid(2)mkdtemp(3)mkstemp(3)mktemp(3)stdio(3)tempnam(3)tmpfile(3)