mkstemp(3) Library Functions Manual mkstemp(3)
NAME
mkstemp, mkostemp, mkstemps, mkostemps - create a unique temporary file
LIBRARY
Standard C library (libc, -lc)
SYNOPSIS
#include <stdlib.h>
int mkstemp(char *template);
int mkostemp(char *template, int flags);
int mkstemps(char *template, int suffixlen);
int mkostemps(char *template, int suffixlen, int flags);
Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
mkstemp():
_XOPEN_SOURCE >= 500
|| /* glibc >= 2.12: */ _POSIX_C_SOURCE >= 200809L
|| /* glibc <= 2.19: */ _SVID_SOURCE || _BSD_SOURCE
mkostemp():
_GNU_SOURCE
mkstemps():
/* glibc >= 2.19: */ _DEFAULT_SOURCE
|| /* glibc <= 2.19: */ _SVID_SOURCE || _BSD_SOURCE
mkostemps():
_GNU_SOURCE
DESCRIPTION
The mkstemp() function generates a unique temporary filename from tem-
plate, creates and opens the file, and returns an open file descriptor
for the file.
The last six characters of template must be "XXXXXX" and these are re-
placed with a string that makes the filename unique. Since it will be
modified, template must not be a string constant, but should be de-
clared as a character array.
The file is created with permissions 0600, that is, read plus write for
owner only. The returned file descriptor provides both read and write
access to the file. The file is opened with the open(2) O_EXCL flag,
guaranteeing that the caller is the process that creates the file.
The mkostemp() function is like mkstemp(), with the difference that the
following bits—with the same meaning as for open(2)—may be specified in
flags: O_APPEND, O_CLOEXEC, and O_SYNC. Note that when creating the
file, mkostemp() includes the values O_RDWR, O_CREAT, and O_EXCL in the
flags argument given to open(2); including these values in the flags
argument given to mkostemp() is unnecessary, and produces errors on
some systems.
The mkstemps() function is like mkstemp(), except that the string in
template contains a suffix of suffixlen characters. Thus, template is
of the form prefixXXXXXXsuffix, and the string XXXXXX is modified as
for mkstemp().
The mkostemps() function is to mkstemps() as mkostemp() is to mk-
stemp().
RETURN VALUE
On success, these functions return the file descriptor of the temporary
file. On error, -1 is returned, and errno is set to indicate the er-
ror.
ERRORS
EEXIST Could not create a unique temporary filename. Now the contents
of template are undefined.
EINVAL For mkstemp() and mkostemp(): The last six characters of tem-
plate were not XXXXXX; now template is unchanged.
For mkstemps() and mkostemps(): template is less than (6 + suf-
fixlen) characters long, or the last 6 characters before the
suffix in template were not XXXXXX.
These functions may also fail with any of the errors described for
open(2).
ATTRIBUTES
For an explanation of the terms used in this section, see attrib-
utes(7).
┌───────────────────────────────────────────┬───────────────┬─────────┐
│ Interface │ Attribute │ Value │
├───────────────────────────────────────────┼───────────────┼─────────┤
│ mkstemp(), mkostemp(), mkstemps(), │ Thread safety │ MT-Safe │
│ mkostemps() │ │ │
└───────────────────────────────────────────┴───────────────┴─────────┘
STANDARDS
mkstemp()
POSIX.1-2001.
mkstemps()
BSD.
mkostemp()
mkostemps()
GNU.
HISTORY
mkstemp()
4.3BSD, POSIX.1-2001.
mkstemps()
glibc 2.11. BSD, Mac OS X, Solaris, Tru64.
mkostemp()
glibc 2.7.
mkostemps()
glibc 2.11.
In glibc versions 2.06 and earlier, the file is created with permis-
sions 0666, that is, read and write for all users. This old behavior
may be a security risk, especially since other UNIX flavors use 0600,
and somebody might overlook this detail when porting programs.
POSIX.1-2008 adds a requirement that the file be created with mode
0600.
More generally, the POSIX specification of mkstemp() does not say any-
thing about file modes, so the application should make sure its file
mode creation mask (see umask(2)) is set appropriately before calling
mkstemp() (and mkostemp()).
SEE ALSO
mkdtemp(3), mktemp(3), tempnam(3), tmpfile(3), tmpnam(3)
Linux man-pages 6.7 2023-10-31 mkstemp(3)
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