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RTL Differences

When porting a Fortran application, most of the RTL routine calls will need to be modified slightly, due to the need for an argument list terminator and the elimination of optional arguments. A portable application must use the new rules below when calling the RTL. Although following the old calling conventions instead will work under VMS, they will work only under VMS. To be portable, the new conventions must be used.

The new RTL calling sequence is described in detail in Section , RTL Calling Conventions. As a reminder, the highlights are listed again below.

• Terminator. All RTL routines with keyword-value pairs of optional arguments must have a terminator in the argument list, even if none of the optional arguments are used.

• Character strings. All strings input to the RTL must be CHARACTER*n variables or constants. Formerly, BYTE or LOGICAL*1 arrays were allowed in RTL arguments, but no longer. BYTE and LOGICAL*1 do not have a string length indication, and there is no way for the routine to tell whether the argument is a CHARACTER*n (which does have a length), or a byte array. Since the length is required, BYTE and LOGICAL*1 no longer work. This applies both to string arguments and to keywords in the keyword-value pairs, since they are strings also. The change to CHARACTER*n is going to be most troublesome with the output routines xvmessage and qprint, since they are often called with BYTE arrays. See Section , READ & WRITE to Strings, below, for details on new methods of doing string output.

• Optional arguments. Pure optional arguments are not allowed. Most routines require all arguments to be specified, but a few have had some removed. See Table for a list of all the optional argument routines.