Procedure

     EXISTS ( Does the file exist? )

     LOGICAL FUNCTION  EXISTS ( FNAME )

Abstract

     Determine whether a file exists.

Required_Reading

     None.

Keywords

     FILES

Declarations

     IMPLICIT NONE

     CHARACTER*(*)    FNAME

Brief_I/O

     VARIABLE  I/O  DESCRIPTION
     --------  ---  --------------------------------------------------
     FNAME      I   Name of the file in question.

     The function returns the value .TRUE. if the file exists, .FALSE.
     otherwise.

Detailed_Input

     FNAME    is the name of the file in question. This may be any
              unambiguous file name valid on the user's computer, for
              example

                 '/usr/dir1/dir2/DATA.DAT'
                 './DATA.DAT'
                 'c:\usr\dir1\dir2\data.dat'

              Environment or shell variables may not be used.

Detailed_Output

     The function returns the value .TRUE. if the file exists, .FALSE.
     otherwise.

Parameters

     None.

Exceptions

     1)  If the filename is blank, the error SPICE(BLANKFILENAME) is
         signaled.

     2)  If an I/O error occurs while checking the existence of the
         indicated file, the error SPICE(INQUIREFAILED) is signaled.

Files

     None.

Particulars

     Use the Fortran INQUIRE statement to determine the existence
     of FNAME.

Examples

     The numerical results shown for this example may differ across
     platforms. The results depend on the SPICE kernels used as
     input, the compiler and supporting libraries, and the machine
     specific arithmetic implementation.

     1) Given two arbitrary files (one of them the actual code example
        source file), determine if they exists.

        Example code begins here.


              PROGRAM EXISTS_EX1
              IMPLICIT NONE

        C
        C     SPICELIB functions.
        C
              LOGICAL                 EXISTS
              INTEGER                 RTRIM

        C
        C     Local constants.
        C
              INTEGER                 FILEN
              PARAMETER             ( FILEN = 14 )

        C
        C     Local variables.
        C
              CHARACTER*(FILEN)       FNAME  ( 2 )

              INTEGER                 I

        C
        C     Define an array of file names.
        C
              DATA                    FNAME / 'exists_ex1.txt',
             .                                'exists_ex1.pgm' /

              DO I = 1, 2

                 IF ( EXISTS ( FNAME(I) ) ) THEN

                    WRITE(*,*) 'The file ', FNAME(I)(:RTRIM(FNAME(I))),
             .                 ' exists.'

                 ELSE

                    WRITE(*,*) 'Cannot find the file ', FNAME(I)

                 END IF

              END DO

              END


        When this program was executed on a Mac/Intel/gfortran/64-bit
        platform, the output was:


         Cannot find the file exists_ex1.txt
         The file exists_ex1.pgm exists.

Restrictions

     None.

Literature_References

     None.

Author_and_Institution

     N.J. Bachman       (JPL)
     J. Diaz del Rio    (ODC Space)
     K.R. Gehringer     (JPL)
     H.A. Neilan        (JPL)
     W.L. Taber         (JPL)
     I.M. Underwood     (JPL)

Version

    SPICELIB Version 2.3.0, 17-JUN-2021 (JDR)

        Edited the header to comply with NAIF standard.
        Added complete code example.

        Changed input argument name FILE to FNAME for consistency with
        other routines.

        Added IMPLICIT NONE statement.

    SPICELIB Version 2.2.1, 01-JUL-2014 (NJB)

        VAX examples were deleted from the header.

    SPICELIB Version 2.2.0, 09-DEC-1999 (WLT)

        The input file name is now "trimmed" of trailing blanks
        before checking its existence.

    SPICELIB Version 2.1.0, 04-MAR-1996 (KRG)

        Added a local logical variable that is used as temporary
        storage for the results from the INQUIRE statement rather
        than using the function name. This solved a problem on the
        macintosh.

    SPICELIB Version 2.0.0, 04-AUG-1994 (KRG)

        Added a test to see if the filename was blank before the
        INQUIRE statement. This allows a meaningful error message to
        be presented.

    SPICELIB Version 1.1.0, 17-MAY-1994 (HAN)

        If the value of the function RETURN is .TRUE. upon execution of
        this module, this function is assigned a default value of
        either 0, 0.0D0, .FALSE., or blank depending on the type of
        the function.

    SPICELIB Version 1.0.1, 10-MAR-1992 (WLT)

        Comment section for permuted index source lines was added
        following the header.

    SPICELIB Version 1.0.0, 31-JAN-1990 (IMU)