tmpnam(S)                      6 January 1993                      tmpnam(S)


 Name

    tmpnam, tempnam - create a name for a temporary file

 Syntax


    cc ... -lc


    #include <stdio.h>

    char *tmpnam (s)
    char *s;

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


 Description

    These functions generate filenames that are not the same as name of an
    existing file.

    The tmpnam function always generates a filename using the path-prefix
    defined as Ptmpdir in the <stdio.h> header file. The generated filename
    is different each time that tmpnam is called from the same process, up to
    TMPMAX times.  If s is NULL, tmpnam leaves its result in an internal
    static area and returns a pointer to that area.  The next call to tmpnam
    destroys the contents of the area.  If s is not NULL, it is assumed to be
    the address of an array of at least Ltmpnam bytes, where Ltmpnam is a
    constant defined in <stdio.h>; tmpnam places its result in that array and
    returns s.

    tempnam allows choosing a directory.  The argument dir points to the name
    of the directory in which the file is to be created.  If dir is NULL or
    points to a string that is not a name for an appropriate directory, the
    path-prefix defined as Ptmpdir in the <stdio.h> header file is used.  If
    that directory is not accessible, /tmp is used as a last resort.  This
    entire sequence can be up-staged by providing an environment variable
    TMPDIR in the user's environment, whose value is the name of the desired
    temporary-file directory.

    Many applications prefer their temporary files to have certain favorite
    initial letter sequences in their names.  Use the pfx argument for this.
    This argument may be NULL or point to a string of up to five characters
    to be used as the first few characters of the temporary-filename.

 Return value

    tempnam uses malloc(S) to get space for the constructed filename and
    returns a pointer to this area.  Thus, any pointer value returned from
    tempnam may serve as an argument to free (see malloc(S)).

    If tempnam cannot return the expected result for any reason, i.e.,
    malloc(S) failed, or none of the above mentioned attempts to find an
    appropriate directory was successful, a NULL pointer is returned.

 Diagnostics

    The tempnam function will fail if:

    [ENOMEM]       Insufficient storage space is available.

 Notes

    These functions generate a different filename each time they are called.

    Files created using these functions and either fopen(S) or creat(S) are
    temporary only in the sense that they reside in a directory intended for
    temporary use, and their names are unique.  It is the user's responsibil-
    ity to use unlink(S) to remove the file when its use is ended.

    If called more than 17,576 times in a single process, these functions
    recycle previously used names.

    Between the time a filename is created and the file is opened, it is pos-
    sible for some other process to create a file with the same name.  This
    can never happen if that other process is using these functions or
    mktemp, and the filenames are chosen to render duplication by other means
    unlikely.

 See also

    creat(S), fopen(S), malloc(S), mktemp(S), tmpfile(S), unlink(S)

 Standards conformance

    tmpnam is conformant with:
    AT&T SVID Issue 2;
    X/Open Portability Guide, Issue 3, 1989;
    ANSI X3.159-1989 Programming Language -- C;
    IEEE POSIX Std 1003.1-1990 System Application Program Interface (API) [C
    Language] (ISO/IEC 9945-1);
    and NIST FIPS 151-1.