MKSTEMP(3)



MKSTEMP(3)                 Linux Programmer's Manual                MKSTEMP(3)

NAME
       mkstemp, mkostemp, mkstemps, mkostemps - create a unique temporary file

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
               || /* Since glibc 2.12: */ _POSIX_C_SOURCE >= 200809L
               || /* Glibc versions <= 2.19: */ _SVID_SOURCE || _BSD_SOURCE

       mkostemp(): _GNU_SOURCE
       mkstemps():
           /* Glibc since 2.19: */ _DEFAULT_SOURCE
               || /* Glibc versions <= 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 appropriately.

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).

VERSIONS
       mkostemp()  is  available  since glibc 2.7.  mkstemps() and mkostemps()
       are available since glibc 2.11.

ATTRIBUTES
       For an  explanation  of  the  terms  used  in  this  section,  see  at-
       tributes(7).

       +------------------------+---------------+---------+
       |Interface               | Attribute     | Value   |
       +------------------------+---------------+---------+
       |mkstemp(), mkostemp(),  | Thread safety | MT-Safe |
       |mkstemps(), mkostemps() |               |         |
       +------------------------+---------------+---------+
CONFORMING TO
       mkstemp(): 4.3BSD, POSIX.1-2001.

       mkstemps(): unstandardized, but appears on several other systems.

       mkostemp() and mkostemps(): are glibc extensions.

NOTES
       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)

COLOPHON
       This  page  is  part of release 4.16 of the Linux man-pages project.  A
       description of the project, information about reporting bugs,  and  the
       latest     version     of     this    page,    can    be    found    at
       https://www.kernel.org/doc/man-pages/.

GNU                               2017-09-15                        MKSTEMP(3)

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