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MKSTEMP(3) Linux Programmer's Manual MKSTEMP(3)
mkstemp - create a unique temporary file
int mkstemp(char *template);
The mkstemp() function generates a unique temporary file name from template. The last six
characters of template must be XXXXXX and these are replaced with a string that makes the
filename unique. The file is then created with mode read/write and permissions 0666 (glibc
2.0.6 and earlier), 0600 (glibc 2.0.7 and later). Since it will be modified, template
must not be a string constant, but should be declared as a character array. The file is
opened with the O_EXCL flag, guaranteeing that when mkstemp returns successfully we are
the only user.
The mkstemp() function returns the file descriptor fd of the temporary file or -1 on
EINVAL The last six characters of template were not XXXXXX. Now template is unchanged.
EEXIST Could not create a unique temporary filename. Now the contents of template are
The old behaviour (creating a file with mode 0666) may be a security risk, especially
since other Unix flavours use 0600, and somebody might overlook this detail when porting
More generally, the POSIX specification does not say anything about file modes, so the
application should make sure its umask is set appropriately before calling mkstemp.
BSD 4.3, POSIX 1003.1-2001
The prototype is in <unistd.h> for libc4, libc5, glibc1; glibc2 follows the Single Unix
Specification and has the prototype in <stdlib.h>.
mkdtemp(3), mktemp(3), tmpnam(3), tempnam(3), tmpfile(3)
GNU 2001-12-23 MKSTEMP(3)
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