tempnam(3)



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

NAME
       tempnam - create a name for a temporary file

SYNOPSIS
       #include <stdio.h>

       char *tempnam(const char *dir, const char *pfx);

   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

       tempnam():
           Since glibc 2.19:
               _DEFAULT_SOURCE
           Glibc 2.19 and earlier:
               _BSD_SOURCE || _SVID_SOURCE

DESCRIPTION
       Never use this function.  Use mkstemp(3) or tmpfile(3) instead.

       The  tempnam()  function  returns a pointer to a string that is a valid
       filename, and such that a file with this name did not exist when  temp-
       nam()  checked.   The  filename  suffix  of the pathname generated will
       start with pfx in case pfx is a non-NULL string of at most five  bytes.
       The  directory  prefix part of the pathname generated is required to be
       "appropriate" (often that at least implies writable).

       Attempts to find an appropriate  directory  go  through  the  following
       steps:

       a) In case the environment variable TMPDIR exists and contains the name
          of an appropriate directory, that is used.

       b) Otherwise, if the dir argument is non-NULL and  appropriate,  it  is
          used.

       c) Otherwise, P_tmpdir (as defined in <stdio.h>) is used when appropri-
          ate.

       d) Finally an implementation-defined directory may be used.

       The string returned by tempnam() is allocated using malloc(3) and hence
       should be freed by free(3).

RETURN VALUE
       On success, the tempnam() function returns a pointer to a unique tempo-
       rary filename.  It returns NULL if a unique name cannot  be  generated,
       with errno set to indicate the cause of the error.

ERRORS
       ENOMEM Allocation of storage failed.

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

       +----------+---------------+-------------+
       |Interface | Attribute     | Value       |
       +----------+---------------+-------------+
       |tempnam() | Thread safety | MT-Safe env |
       +----------+---------------+-------------+
CONFORMING TO
       SVr4, 4.3BSD, POSIX.1-2001.  POSIX.1-2008 marks tempnam() as obsolete.

NOTES
       Although tempnam() generates names that are difficult to guess,  it  is
       nevertheless  possible  that  between the time that tempnam() returns a
       pathname, and the time that the program opens it, another program might
       create  that  pathname  using open(2), or create it as a symbolic link.
       This can lead to security holes.  To avoid such possibilities, use  the
       open(2)  O_EXCL  flag  to  open  the  pathname.  Or better yet, use mk-
       stemp(3) or tmpfile(3).

       SUSv2 does not mention the use of TMPDIR; glibc will use it  only  when
       the  program  is not set-user-ID.  On SVr4, the directory used under d)
       is /tmp (and this is what glibc does).

       Because it dynamically allocates memory used to  return  the  pathname,
       tempnam() is reentrant, and thus thread safe, unlike tmpnam(3).

       The  tempnam()  function  generates  a different string each time it is
       called, up to TMP_MAX (defined in <stdio.h>) times.  If  it  is  called
       more than TMP_MAX times, the behavior is implementation defined.

       tempnam() uses at most the first five bytes from pfx.

       The  glibc implementation of tempnam() fails with the error EEXIST upon
       failure to find a unique name.

BUGS
       The precise meaning of "appropriate" is undefined;  it  is  unspecified
       how accessibility of a directory is determined.

SEE ALSO
       mkstemp(3), mktemp(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/.

                                  2017-09-15                        TEMPNAM(3)

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