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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
     attributes(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
     mkstemp(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.