Re: QMHCHGEM API & Invocation pointer -- RPG400-L


On 26/02/2005, at 9:35 AM, Paul Jackson wrote:

I am trying to use the QMHCHGEM (Change exception message) API as a default handling program for a particular message ID. Unfortunately the API requires an "invocation pointer". The handling program is passed program queue and message key information but not pointer.

This API is not designed for use from anything except C. C supports invocation pointers directly but you can often fake them with RPG pointers as long as you do nothing other than set them and pass them around.

The API should have allowed an invocation pointer OR the usual program/module/procedure method like most of the other MH APIs. I see QMHPRMM also expects an invocation pointer.

I have been searching through the API's on the web with no luck and am wondering if there's a method I can use to retrieve the invocation pointer for passing to the API.

You can pass a NULL pointer (which means your current invocation i.e., the invocation that calls QMHCHGEM) and use the call stack counter to determine the relative invocation.

If that's not suitable then the C interface to MI functions may help you.

_INVP(0) will return an invocation pointer to the caller's invocation. Perhaps your caller could use this and pass the invocation pointer to you?

fndrinvn() will search for a specified invocation. In your case you would probably want to get a system pointer to the program (using the program queue name and the rslvsp() function). This will return a relative invocation number which you could use on the call stack counter parameter of QMHCHGEM in conjunction with a NULL invocation pointer.

matinvs() will materialise the invocation stack in a variable (or space) that you could then search for matching program. You would need to materialise the program pointer in each invocation entry using matptr() and check if the object name matched the program name. When you found that you could use its invocation number and your own invocation number to derive a relative invocation value for use on the call stack counter parameter of QMHCHGEM.

There may be other methods too but these are the ones that occur too me.

Any help would be appreciated.

The real question is why are you doing this? What are you trying to accomplish?

Regards,
Simon Coulter.
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