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The BEGINCALL allows you to call more complex COM methods. The normal CALL service only allows you to pass values. However, some COM methods behave differently if you omit parameters, or you might need to pass objects as parameters. In those cases, you will use this service to begin a multi-step process that includes this service along with the ADDPARAM and ENDCALL services.

Note that you do not specify the method name here, nor do you pass a handle to a COM object. You will do that when you use the ENDCALL service.


Here is a real world use case. In the Excel object model, there is a ListObjects class. You can add a variety of Excel objects to this class, and if you add a Range to it, there is a parameter that you must omit or the method will fail. This means we need that ability to pass an object and omit a parameter. The CALL service can't do this for us, so we'll use BEGINCALL...ENDCALL instead.