tmpnam, tempnam

Purpose

     Constructs the name for a temporary file.

Library

     Standard I/O Library (libc.a)

Syntax

     #include <stdio.h>

       char *tmpnam (s)                          char *tempnam (dir, pfx)
       char *s;                                  char *dir, *pfx;
     Description

     The tmpnam  and tempnam  subroutines generate  file names
     for temporary files.

     The  tmpnam subroutine  generates a  file name  using the
     path name defined as P_tmpdir in the stdio.h header file.
     If the s parameter is  NULL, the tmpnam subroutine places
     its result  into an  internal static  area and  returns a
     pointer to that  area.  The next call  to this subroutine
     destroys the contents of the area.

     If the s  parameter is not NULL, it is  assumed to be the
     address of an array of at least the number of bytes spec-
     ified  by L_tmpnam.   L_tmpnam is  a constant  defined in
     stdio.h.  The  tmpnam subroutine places its  results into
     that array and returns the value of the s parameter.

     The tempnam  subroutine allows you to  control the choice
     of a  directory.  The  dir parameter  points to  the path
     name of the directory in which the file is to be created.
     If the dir parameter is NULL  or points to a string which
     is not a path name for an appropriate directory, the path
     name defined  as P_tmpdir in  the stdio.h header  file is
     used.  If that path name is not accessible, /tmp is used.
     You can bypass the selection  of a path name by providing
     an environment  variable, TMPDIR, in the  user's environ-
     ment.  The  value of the  TMPDIR variable is a  path name
     for the desired temporary-file  directory.  If the TMPDIR
     variable is used, both the dir parameter and L_tmpnam are
     ignored.

     The pfx  parameter of the tempname  subroutine allows you
     to specify  an initial character sequence  with which the
     file name begins.   The pfx parameter can be  NULL, or it
     can point to a string of up to five characters to be used
     as the first few characters of the temporary file name.

     The  tempnam subroutine  uses  the  malloc subroutine  to
     obtain space  for the constructed file  name.  The return
     value is a pointer to this space.  Therefore, the pointer
     value returned by  tempnam can be used as  a parameter to
     the free subroutine.

     If  the tempnam  subroutine  cannot  return the  expected
     result for any reason (for example, if the malloc subrou-
     tine  fails, or  if  an appropriate  directory cannot  be
     found), then it returns a NULL pointer.

     Warning:  The  tmpnam and tempnam subroutines  generate a
     different file name  each time they are  called.  If they
     are called  more than  4,096 times  by a  single process,
     they start recycling previously used names.

     Files created using these  subroutines reside in a direc-
     tory  intended for  temporary  use, and  their names  are
     unique.   It is  your  responsibility to  use the  unlink
     system call to remove the file when no longer needed.

     Between the time  a file name is created and  the file is
     opened, it is possible for some other process to create a
     file with the same name.   This should not happen if that
     other process  uses these subroutines or  the mktemp sub-
     routine, and if the file  names are chosen to make dupli-
     cation by other means unlikely.

     Related Information

     In  this  book:    "creat,"  "unlink,"  "fopen,  freopen,
     fdopen,"  "malloc,  free,   realloc,  calloc,"  "mktemp,"
     "tmpfile," and "environment."