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



NAME
       tempnam - create a name for a temporary file

SYNOPSIS
       #include <stdio.h>

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

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

       tempnam(): _BSD_SOURCE || _SVID_SOURCE

DESCRIPTION
       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 "appro‐
       priate" (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
       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 cause of
       the error.

ERRORS
       ENOMEM Allocation of storage failed.

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

NOTES
       Although  tempnam() generates names that are difficult to guess, it is nevertheless possi‐
       ble 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 sym‐
       bolic 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  reen‐
       trant, 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() will fail with the error EEXIST upon failure to find
       a unique name.

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

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

COLOPHON
       This  page  is  part of release 3.74 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 http://www.kernel.org/doc/man-pages/.



                                            2014-02-27                                 TEMPNAM(3)