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
       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 "appropri-
       ate" (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
       The tempnam() function returns a pointer to a unique temporary filename, or NULL if a unique name cannot be generated.

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 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() 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.

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

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

COLOPHON
       This page is part of release 3.25 of the Linux man-pages project.  A description of the project,  and  information  about
       reporting bugs, can be found at http://www.kernel.org/doc/man-pages/.



                                                           2008-08-06                                                 TEMPNAM(3)