NAME
tempnam, tmpfile, tmpnam - temporary file routines

SYNOPSIS
FILE *tmpfile()

char *tmpnam(str)
char *str;

char *tempnam(tmpdir, prefix)
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 X3.159-1989.

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.