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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)