tempnam(3) — Linux manual page

NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | ATTRIBUTES | CONFORMING TO | NOTES | BUGS | SEE ALSO | COLOPHON

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

NAME         top

       tempnam - create a name for a temporary file

SYNOPSIS         top

       #include <stdio.h>

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

   Feature Test Macro Requirements for glibc (see
   feature_test_macros(7)):

       tempnam():
           Since glibc 2.19:
               _DEFAULT_SOURCE
           Glibc 2.19 and earlier:
               _BSD_SOURCE || _SVID_SOURCE

DESCRIPTION         top

       Never use this function.  Use mkstemp(3) or tmpfile(3) instead.

       The tempnam() function returns a pointer to a string that is a
       valid filename, and such that a file with this name did not exist
       when tempnam() checked.  The filename suffix of the pathname
       generated will start with pfx in case pfx is a non-NULL string of
       at most five bytes.  The directory prefix part of the pathname
       generated is required to be "appropriate" (often that at least
       implies writable).

       Attempts to find an appropriate directory go through the
       following steps:

       a) In case the environment variable TMPDIR exists and contains
          the name of an appropriate directory, that is used.

       b) Otherwise, if the dir argument is non-NULL and appropriate, it
          is used.

       c) Otherwise, P_tmpdir (as defined in <stdio.h>) is used when
          appropriate.

       d) Finally an implementation-defined directory may be used.

       The string returned by tempnam() is allocated using malloc(3) and
       hence should be freed by free(3).

RETURN VALUE         top

       On success, the tempnam() function returns a pointer to a unique
       temporary filename.  It returns NULL if a unique name cannot be
       generated, with errno set to indicate the error.

ERRORS         top

       ENOMEM Allocation of storage failed.

ATTRIBUTES         top

       For an explanation of the terms used in this section, see
       attributes(7).

       ┌──────────────────────────────────┬───────────────┬─────────────┐
       │Interface                         Attribute     Value       │
       ├──────────────────────────────────┼───────────────┼─────────────┤
       │tempnam()                         │ Thread safety │ MT-Safe env │
       └──────────────────────────────────┴───────────────┴─────────────┘

CONFORMING TO         top

       SVr4, 4.3BSD, POSIX.1-2001.  POSIX.1-2008 marks tempnam() as
       obsolete.

NOTES         top

       Although tempnam() generates names that are difficult to guess,
       it is nevertheless possible that between the time that tempnam()
       returns a pathname, 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).

       SUSv2 does not mention the use of TMPDIR; glibc will use it only
       when the program is not set-user-ID.  On SVr4, the directory used
       under d) is /tmp (and this is what glibc does).

       Because it dynamically allocates memory used to return the
       pathname, tempnam() is reentrant, and thus thread safe, unlike
       tmpnam(3).

       The tempnam() function generates a different string each time it
       is called, up to TMP_MAX (defined in <stdio.h>) times.  If it is
       called more than TMP_MAX times, the behavior is implementation
       defined.

       tempnam() uses at most the first five bytes from pfx.

       The glibc implementation of tempnam() fails with the error EEXIST
       upon failure to find a unique name.

BUGS         top

       The precise meaning of "appropriate" is undefined; it is
       unspecified how accessibility of a directory is determined.

SEE ALSO         top

       mkstemp(3), mktemp(3), tmpfile(3), tmpnam(3)

COLOPHON         top

       This page is part of release 5.12 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
       https://www.kernel.org/doc/man-pages/.

                               2021-03-22                     TEMPNAM(3)

Pages that refer to this page: getpid(2)mkdtemp(3)mkstemp(3)mktemp(3)stdio(3)tmpfile(3)tmpnam(3)environ(7)