TMPFILE(3)                386BSD Programmer's Manual                TMPFILE(3)

NAME
     tempnam, tmpfile, tmpnam - temporary file routines

SYNOPSIS
     #include <stdio.h>

     FILE *
     tmpfile(void)

     char *
     tmpnam(char *str)

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

DESCRIPTION
     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 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 dir (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).

RETURN VALUES
     The tmpfile() function returns a pointer to an open file stream on
     success, and a NULL pointer on error.

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

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

     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).

SEE ALSO
     mkstemp(3),  mktemp(3)

STANDARDS
     The tmpfile() and tmpnam() functions conform to ANSI C3.159-1989 (``ANSI
     C'').

BUGS
     These interfaces are provided for System V 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.  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)  use the access(2) function 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 created.

     This implementation does not have these flaws, 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.

BSD Experimental                 June 29, 1991                               2