Entry Point Mapping for COBOL Programs

The Entry Point Mapper enables you to specify entry points in COBOL programs so that the application can find them at run time. You need to do this for any entry points in programs that will not have been loaded prior to them being called.

To appreciate why and when to use this facility, you need to understand how calls to entry points are resolved by the run-time system:

• When a program makes a call to an entry point, the run-time system looks for the entry point to resolve it dynamically.
• When the program is loaded, the name of the program and all the entry points in the program are recorded in a table. When a call to an entry point is made, the run-time system searches the table for the entry point name. If it does not find the entry point name, it looks on disk for an executable file of the same name.
• Consequently, if your program calls an entry point that is not the name of an executable file and is not an entry point in a previously loaded program, the run-time system cannot find the entry point and your program fails. This is when you need to use the Entry Point Mapper.

Entry points are often not found when you take code that has been downloaded from a mainframe to the PC for further development. Mainframe programs often have several entry points in a single program. On the mainframe, entry points are resolved by linking, so calls can be made to a program and the entry point located whether or not the program has been called. Using your COBOL development system, if the program containing the entry point has not already been called, the call to that entry point fails.

To ensure the entry points are found, you use the Entry Point Mapper. You create an entry name map file containing an entry point table and make it available to the run-time system.