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MKTEMP(3)	       FreeBSD 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	suit-
     able 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
     creates the template file,	mode 0600, returning a file descriptor opened
     for reading and writing.  This avoids the race between testing for	a
     file's existence and opening it for use.

     The mkdtemp() function makes the same replacement to the template as in
     mktemp(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
     suitable 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 follow-
     ing 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
     specified 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'') compilers were common.  For	example, calling mkstemp()
     with an argument of "/tmp/tempfile.XXXXXX"	will result in a core dump due
     to	mkstemp() attempting to	modify the string constant that	was given.  If
     the program in question 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	9.2		       February	11, 1998		   FreeBSD 9.2

NAME | SYNOPSIS | DESCRIPTION | RETURN VALUES | ERRORS | NOTES | BUGS | SEE ALSO | HISTORY

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