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 direc-tory. directory.
tory. 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 refer-ence reference
ence 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. Other-wise, Otherwise,
wise, 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 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 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).
SECURITY CONSIDERATIONS
The tmpnam() and tempnam() functions are susceptible to a race condition occurring between the selec-tion selection
tion of the file name and the creation of the file, which allows malicious users to potentially over-write overwrite
write arbitrary files in the system, depending on the level of privilege of the running program. Addi-tionally, Additionally,
tionally, 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.)
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.
SEE ALSO
mkstemp(3), mktemp(3)
STANDARDS
The tmpfile() and tmpnam() functions conform to ISO/IEC 9899:1990 (``ISO C90'').
BSD November 17, 1993 BSD
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