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MKTEMP(3)		     Library Functions Manual		       MKTEMP(3)

NAME
     mktemp -- make temporary file name (unique)

SYNOPSIS
     #include <unistd.h>

     char *
     mktemp(char *template);

     int
     mkstemp(char *template);

     char *
     mkdtemp(char *template);

DESCRIPTION
     The  mktemp()  function takes the given file name template and overwrites a
     portion of it to create a file name.  This file name is unique and suitable
     for use by the application.  The template may be any file	name  with  some
     number  of  `Xs'  appended to it, for example /tmp/temp.XXXX.  The trailing
     `Xs' are replaced with the current process number and/or  a  unique  letter
     combination.   The  number of unique file names mktemp() can return depends
     on the number of `Xs' provided; six `Xs' will result  in  mktemp()  testing
     roughly 26 ** 6 combinations.

     The  mkstemp() function makes the same replacement to the template and cre-
     ates the template file, mode 0600, returning a file descriptor  opened  for
     reading and writing.  This avoids the race between testing for a file's ex-
     istence and opening it for use.

     The mkdtemp() function makes the same replacement to the template as in mk-
     temp(3) and creates the template directory, mode 0700.

RETURN VALUES
     The  mktemp()  and  mkdtemp() functions return a pointer to the template on
     success and NULL on failure.  The mkstemp() function returns -1 if no suit-
     able file could be created.  If either call fails an error code  is  placed
     in the global variable errno.

ERRORS
     The mkstemp() and mkdtemp() functions may set errno to one of the following
     values:

     [ENOTDIR]	The  pathname  portion of the template is not an existing direc-
		tory.

     The mkstemp() and mkdtemp() functions may also set errno to any value spec-
     ified by the stat(2) function.

     The mkstemp() function may also set errno to any  value  specified  by  the
     open(2) function.

     The  mkdtemp()  function  may  also set errno to any value specified by the
     mkdir(2) function.

NOTES
     A common problem that results in a core dump is that the programmer  passes
     in  a read-only string to mktemp(), mkstemp() or mkdtemp().  This is common
     with programs that were developed before ANSI X3.159-1989 ("ANSI C89") com-
     pilers were common.  For example, calling mkstemp()  with	an  argument  of
     "/tmp/tempfile.XXXXXX" will result in a core dump due to mkstemp() attempt-
     ing  to modify the string constant that was given.  If the program in ques-
     tion makes heavy use of that type of function call, you do have the  option
     of  compiling  the  program  so  that  it	will store string constants in a
     writable segment of memory.  See gcc(1) for more information.

BUGS
     An attacker can guess the filenames produced by mktemp().	Whenever  it  is
     possible mkstemp() should be used instead.

SEE ALSO
     chmod(2), getpid(2), mkdir(2), open(2), stat(2)

HISTORY
     A	mktemp()  function appeared in Version 7 AT&T UNIX.  The mkdtemp() func-
     tion first appeared in OpenBSD 2.2.

FreeBSD 2.2.7			February 11, 1998		       MKTEMP(3)
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