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TMPFILE(3)                 Library Functions Manual                 TMPFILE(3)

     tempnam, tmpfile, tmpnam - temporary file routines

     Standard C Library (libc, -lc)

     #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 mode `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 s 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 s 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()
     allocates 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
     success, 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.

     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
     specified for the library function mktemp(3).

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

     mkstemp(3), mktemp(3)

     The tmpfile() and tmpnam() functions conform to ANSI X3.159-1989
     ("ANSI C89").  All described functions also conform to IEEE Std
     1003.1-2001 ("POSIX.1"), albeit the tempnam() and tmpnam() functions have
     been marked as obsolete in the IEEE Std 1003.1-2008 ("POSIX.1") revision.

     These interfaces are provided for AT&T System V UNIX and ANSI
     compatibility only.  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
     between file name selection and file creation and deletion: the program
     is typically written to call tmpnam(), tempnam(), or mktemp(3).
     Subsequently, 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 AT&T System V UNIX implementations of these
     functions (and of mktemp(3)) use the access(2) system call to determine
     whether or not the temporary file may be created.  This has obvious
     ramifications for setuid or 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

     This implementation of tmpfile() does not have these flaws, and that of
     tmpnam() and tempnam() only have the first limitation, but portable
     software cannot depend on that.  In particular, the tmpfile() interface
     should not be used in software expected to be used on other systems if
     there is any possibility that the user does not wish the temporary file
     to be publicly readable and writable.

     A link-time warning will be issued if tmpnam() or tempnam() is used, and
     advises the use of mkstemp() instead.

NetBSD 9.99                     April 30, 2010                     NetBSD 9.99