The Open service makes an existing file available for processing
    by your program. The Open service specifies the type of record
    access to be used and determines whether the file can be shared.
    The Open service also performs an implicit Display service. The
    maximum number of files that can be open within an image at one
    time is 16383.

    Format

      SYS$OPEN  fab [,[err] [,suc]]

1  –  Returns

    OpenVMS usage:cond_value
    type:         longword
    access:       write only
    mechanism:    by value

    The value is returned in symbolic offset FAB$L_STS. Symbolic
    offset FAB$L_STV may contain additional status information.

2  –  Arguments

 fab

    OpenVMS usage:fab
    type:         longword (unsigned)
    access:       modify
    mechanism:    by reference

    FAB control block whose contents are to be used as indirect
    arguments for the Open service call. The fab argument is the
    address of the FAB control block.

 err

    OpenVMS usage:ast_procedure
    type:         procedure value
    access:       call without stack unwinding
    mechanism:    by reference

    AST-level error completion routine that the service invokes if
    the operation is unsuccessful. The err argument is the address of
    the entry mask of this user-written completion routine.

 suc

    OpenVMS usage:ast_procedure
    type:         procedure value
    access:       call without stack unwinding
    mechanism:    by reference

    AST-level success completion routine that the service invokes if
    the operation is successful. The suc argument is the address of
    the entry mask of this user-written completion routine.

3  –  Condition Values Returned

 The following condition values can be returned. Use the Help Message
 utility to access online message descriptions.