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Synopsis:
    #include <stdio.h>
    int fileno( FILE *stream );

Description:
    The fileno function returns the number of the file handle for the file
    designated by stream.  This number can be used in POSIX input/output
    calls anywhere the value returned by  open can be used.  The following
    symbolic values in <io.h> define the file handles that are associated
    with the C language stdin, stdout, stderr, stdaux, and stdprn files when
    the application is started.

    STDIN_FILENO
        Standard input file number, stdin (0)

    STDOUT_FILENO
        Standard output file number, stdout (1)

    STDERR_FILENO
        Standard error file number, stderr (2)

    STDAUX_FILENO
        Standard auxiliary file number, stdaux (3)

    STDPRN_FILENO
        Standard printer file number, stdprn (4)


Returns:
    The fileno function returns the number of the file handle for the file
    designated by stream.  If an error occurs, a value of -1 is returned and
     errno is set to indicate the error.

See Also:
    open

Example:
    #include <stdio.h>

    void main()
      {
        FILE *stream;

        stream = fopen( "file", "r" );
        printf( "File number is %d\n", fileno( stream ) );
        fclose( stream );
      }

    produces the following:

    File number is 7

Classification:
    POSIX 1003.1

Systems:
    All