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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
       "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

       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 3.35 of the Linux man-pages project.  A
       description of the project, and information about reporting  bugs,  can
       be found at http://man7.org/linux/man-pages/.

                                  2008-08-06                        TEMPNAM(3)