TMPFILE(3) BSD Library Functions Manual TMPFILE(3)NAME
tempnam, tmpfile, tmpnam — temporary file routines
LIBRARY
Standard C Library (libc, -lc)
SYNOPSIS
#include <stdio.h>
FILE *
tmpfile(void);
char *
tmpnam(char *s);
char *
tempnam(const char *dir, const char *pfx);
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+’. If the environment variable TMPDIR is defined,
the file is created in the specified directory. 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 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 argument dir (if non-NULL), the directory P_tmpdir, the environment
variable TMPDIR (if set), the directory /tmp and finally, the current
directory, are tried, in the listed order, as directories in which to
store the temporary file.
The argument pfx, 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).
RETURN VALUES
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.
ENVIRONMENT
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.
COMPATIBILITY
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.
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 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).
SECURITY CONSIDERATIONS
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.)
LEGACY DESCRIPTION
In legacy mode, the order directories are tried by the tempnam() function
is different; the environment variable TMPDIR (if defined) is used first.
SEE ALSOmkstemp(3), mktemp(3)STANDARDS
The tmpfile() and tmpnam() functions conform to ISO/IEC 9899:1990
(“ISO C90”).
BSD November 12, 2008 BSD
