OPEN3() and open3c()

Fortran version:

    LOGICAL FUNCTION  OPEN3( FNAME, FSTATUS, PGNAME )
        CHARACTER*(*), INTENT(IN   ) :: FNAME   !  file name for query
        INTEGER      , INTENT(IN   ) :: FSTATUS !  FSREAD3, FSRDWR3, FSNEW3, FSUNKN3, FSCREA3
        CHARACTER*(*), INTENT(IN   ) :: PGNAME  !  name of calling program

C version:

    int open3c( const char          * fname ,
                const IOAPI_Bdesc3  * bdesc ,
                const IOAPI_Cdesc3  * cdesc ,
                int                   fstatus ,
                const char          * pgname ) ;

See Also:

Also see GETDFILE() and GETEFILE(), for opening Fortran sequential and direct access files by logical name.

Summary:

    FSREAD3==1 for read-only,
    FSRDWR3==2 for read/write/update of existing files,
    FSNEW3 ==3 for read/write of new files (file must not
               already exist),
    FSUNKN3==4 for read/write/update of unknown (new vs. old)
               files.  If file does not exist, create it; 
               else check for consistency with user-supplied
               file description.
    FSCREA3==5 for create/truncate/read/write of files.
               If file exists, delete it; then create a new
               (empty) file according to the user-supplied
               file description

If FNAME is being opened for write, copies scenario description from file with logical name SCENDESC, name PGNAME of the caller, and value of environment variable EXECUTION_ID to the file's history (maintained in the file header).

May be called multiple times for a file (provided you don't attempt to go from readonly to any read/write status).

If file may possibly be created (i.e., if the access mode is either FSNEW3, FSUNKN3, or FSCREA3), the user must supply a file description in the COMMONs in INCLUDE-file FDESC3.EXT (for Fortran) or in the data structures pointed to by arguments bdesc and cdesc (for C). In the latter case, the file description struct pointers are only required when the file is being opened "new" or "unknown".

"Normal" modeling usage should be to open input files as FSREAD3 and output files as FSUNKN3. If you open output files as FSNEW3, you must take care to remove pre-existing files before running your program.

NOTE: Joan Novak (EPA) and Ed Bilicki (MCNC) have declared as a software standard that modeling programs may not use FSCREA3 as the mode for opening files. FSCREA3 is reserved for use by analysis/data extraction programs only.

Preconditions:

FNAME must have length at most 16.

For FSREAD3 or FSRDWR3, file must already exist.

For FSNEW3, file must not already exist.

For FSUNKN3, if the file already exists, the file type, dimensions, time step and variables supplied by the caller must match those on the file. The caller-supplied starting date and time must be a legal output time step in the time step sequence found on the file: for example, if the starting time from the file header is 1997012:120000, and the time step is one hour (10000), then opening this file FSUNKN3 with a caller-supplied starting date and time of 1997012:180000 is OK (that would be time step number 7 for the file-header time step sequence) but a caller-supplied 1997011:120000 is not, since it is before the starting date and time from the file itself.

For FSNEW3, FSUNKN3, or FSCREA3, caller must supply file description (which must follow Models-3 date and time conventions).

I/O API must already be initialized by a call to INIT3() or init3c().

OPEN3() must not be called for read/write/update (FSRDWR3, FSNEW3, FSUNK3, or FSCREA3) on a file already open for read-only (FSREAD3).

OPEN3() must not be called for new (FSNEW3) on a file already open (if the file already exists, that contradicts the "new").

Fortran Usage:

    USE M3UTILIO
    

See the sample programs for usage examples.

    ...
    USE M3UTILIO
    ...
    IF ( OPEN3( 'MYFILE', FSREAD3, 'Myprogram' ) ) THEN
        !!      MYFILE successfully opened for read-only
        ...
    ELSE
        !!   Could not open MYFILE for read-only. See program log 
        !!   for further info.
        ...
    END IF
    ...
        !!    <Fill in the file's description to variables in FDESC3.EXT&gt;
    SDATE3D = 1988021
    ...
    IF ( OPEN3( 'AFILE', FSNEW3, 'Myprogram' ) ) THEN
        !!      AFILE successfully opened as a new file
        ...
    ELSE
        !!   Could not open AFILE as a new file:  probably AFILE already
        !!   exists.  See program log for further info.
        ...
    END IF
    ...
    ...
    !!     <Fill in the file's description to variables in FDESC3.EXT&gt;
    SDATE3D = 1988022
    ...
    IF ( OPEN3( 'BFILE', FSUNKN3, 'Myprogram' ) ) THEN
        !!      BFILE successfully opened as unknown
        ...
    ELSE
        !!   Could not open BFILE as unknown:  probably BFILE already
        !!   exists and has a different description than you gave.
        !!   See program log for further info.
        ...
    END IF
    ...

C Usage:

    ...
    #include "iodecl3.h"
    ...
    IOAPI_Bdesc3 bdesc ;
    IOAPI_Cdesc3 cdesc ;
    ...
    /*  put file description in bdesc and cdesc.  Then: */
    if ( open3c( "MYFILE", &bdesc, &cdesc, FSREAD3, "Myprogram" ) )
        {
            /*  MYFILE successfully opened for read-only  */
        ...
        }
    ... /* etc... */

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