NAME
tempnam, tmpfile,
tmpnam —
temporary file routines
LIBRARY
library “libc”
SYNOPSIS
#include
<stdio.h>
FILE *
tmpfile(void);
char *
tmpnam(char
*str);
char *
tempnam(const
char *tmpdir, const char
*prefix);
DESCRIPTION
Thetmpfile()
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).
RETURN VALUES
The tmpfile() function returns a pointer
to an open file stream on success, and a NULL
pointer on error.
The tmpnam() and
tempnam() 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.TMPDIRis 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 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 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 ALSO
STANDARDS
The tmpfile() and
tmpnam() functions conform to
ISO/IEC 9899:1990
(“ISO C90”).