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322) Why does my callback's client data structure contain incorrect

values when the callback is called?  I created a structure and used a pointer
to it as callback client data.

[Last modified: Apr 95]

Answer:  If your structure is declared as automatic, the callback will
probably not be executed within the structure's scope, so the pointer to the
structure will become invalid.  You can avoid this problem by declaring your
structure external or by allocating with malloc or (in C++) new.

Ken Lee, http://www.rahul.net/kenton/