NAME

       tempnam - create a name for a temporary file

LIBRARY

       Standard C library (libc, -lc)

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 tempnam() 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:

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

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

       (3)  Otherwise, P_tmpdir (as defined in <stdio.h>) is used when appropriate.

       (4)  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 temporary filename.  It returns NULL  if
       a unique name cannot be generated, with errno set to indicate 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 │
       └─────────────────────────────────────────────────────────────────────────┴───────────────┴─────────────┘

STANDARDS

       POSIX.1-2008.

HISTORY

       SVr4, 4.3BSD, POSIX.1-2001.  Obsoleted in POSIX.1-2008.

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 (4) 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)

Linux man-pages 6.16                               2025-05-17                                         tempnam(3)