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TMPNAM(3)	       FreeBSD Library Functions Manual		     TMPNAM(3)

     tempnam, tmpfile, tmpnam -- temporary file	routines

     #include <stdio.h>

     FILE *

     char *
     tmpnam(char *str);

     char *
     tempnam(const char	*tmpdir, const char *prefix);

     The tmpfile() function returns a pointer to a stream associated with a
     file descriptor returned by the routine mkstemp(3).  The created file is
     unlinked before tmpfile() returns,	causing	the file to be automatically
     deleted when the last reference to	it is closed.  The file	is opened with
     the access	value `w+'.

     The tmpnam() function returns a pointer to	a file name, in	the P_tmpdir
     directory,	which did not reference	an existing file at some indeterminate
     point in the past.	 P_tmpdir is defined in	the include file <stdio.h>.
     If	the argument str is non-null, the file name is copied to the buffer it
     references.  Otherwise, the file name is copied to	a static buffer.  In
     either case, tmpnam() returns a pointer to	the file name.

     The buffer	referenced by str is expected to be at least L_tmpnam bytes in
     length.  L_tmpnam is defined in the include file <stdio.h>.

     The tempnam() function is similar to tmpnam(), but	provides the ability
     to	specify	the directory which will contain the temporary file and	the
     file name prefix.

     The environment variable TMPDIR (if set), the argument tmpdir (if non-
     null), the	directory P_tmpdir, and	the directory /tmp are tried, in the
     listed order, as directories in which to store the	temporary file.

     The argument prefix, if non-null, is used to specify a file name prefix,
     which will	be the first part of the created file name.  tempnam() allo-
     cates memory in which to store the	file name; the returned	pointer	may be
     used as a subsequent argument to free(3).

     The tmpfile() function returns a pointer to an open file stream on	suc-
     cess, and a null pointer on error.

     The tmpnam() and tempnam()	functions return a pointer to a	file name on
     success, and a null pointer on error.

     TMPDIR  [tempnam()	only] If set, the directory in which the temporary
	     file is stored.  TMPDIR is	ignored	for processes for which
	     issetugid(2) is true.

     The tmpfile() function may	fail and set the global	variable errno for any
     of	the errors specified for the library functions fdopen(3) or

     The tmpnam() function may fail and	set errno for any of the errors	speci-
     fied for the library function mktemp(3).

     The tempnam() function may	fail and set errno for any of the errors spec-
     ified for the library functions malloc(3) or mktemp(3).

     issetugid(2), mkstemp(3), mktemp(3)

     The tmpfile() and tmpnam()	functions conform to ANSI X3.159-1989
     ("ANSI C89").

     tmpnam() and tempnam() are	provided for System V and ANSI compatibility
     only.  These interfaces are typically not used in safe ways.  The
     mkstemp(3)	interface is strongly preferred.

     There are four important problems with these interfaces (as well as with
     the historic mktemp(3) interface).	 First,	there is an obvious race be-
     tween file	name selection and file	creation and deletion: the program is
     typically written to call tmpnam(), tempnam(), or mktemp(3).  Subse-
     quently, the program calls	open(2)	or fopen(3) and	erroneously opens a
     file (or symbolic link, or	FIFO or	other device) that the attacker	has
     placed in the expected file location.  Hence mkstemp(3) is	recommended,
     since it atomically creates the file.

     Second, most historic implementations provide only	a limited number of
     possible temporary	file names (usually 26)	before file names will start
     being recycled.  Third, the System	V implementations of these functions
     (and of mktemp(3))	use the	access(2) function to determine	whether	or not
     the temporary file	may be created.	 This has obvious ramifications	for
     daemons or	setuid/setgid programs,	complicating the portable use of these
     interfaces	in such	programs.  Finally, there is no	specification of the
     permissions with which the	temporary files	are created.

     This implementation does not have these flaws, but	portable software can-
     not depend	on that.

     For these reasons,	ld(1) will output a warning message whenever it	links
     code that uses the	functions tmpnam() or tempnam().

FreeBSD	13.0			August 30, 2019			  FreeBSD 13.0


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