TMPFILE(3) BSD Programmer's Manual TMPFILE(3)
tempnam, tmpfile, tmpnam - temporary file routines
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 s is non-NULL, the file name is copied to the buffer it ref-
erences. Otherwise, the file name is copied to a static buffer. In ei-
ther 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() 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 tempfile() 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 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).
The tmpfile() and tmpnam() functions conform to ANSI C X3.159-1989
(``ANSI C '').
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 be-
tween file name selection and file creation and deletion. Second, most
historic implementations provide only a limited number of possible tempo-
rary 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 pro-
grams, complicating the portable use of these interfaces in such pro-
grams. 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. 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.
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