TMPFILE(3) BSD Library Functions Manual TMPFILE(3)NAME
tempnam, tmpfile, tmpnam — temporary file routines
Standard C Library (libc, -lc)
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 file is created in the directory determined
by the environment variable TMPDIR if set. The default location if
TMPDIR is not set is /tmp.
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. The tempnam()
function 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 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.
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.
These interfaces are provided from System V and ANSI compatibility only.
Most historic implementations of these functions provide only a limited
number of possible temporary file names (usually 26) before file names
will start being recycled. System V 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.
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.
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 tmpnam() and tempnam() functions are susceptible to a race condition
occurring between the selection of the file name and the creation of the
file, which allows malicious users to potentially overwrite arbitrary
files in the system, depending on the level of privilege of the running
program. Additionally, there is no means by which file permissions may
be specified. It is strongly suggested that mkstemp(3) be used in place
of these functions. (See the FSA.)
SEE ALSOmkstemp(3), mktemp(3)STANDARDS
The tmpfile() and tmpnam() functions conform to ISO/IEC 9899:1990
BSD March 18, 2007 BSD