4.6.8 Retaining arguments sent to dispatch methods

When an Automation server receives a string or array as a method argument, it is temporarily allocated a value (an instance of <ole-array>, <BSTR>, or <ole-vector>) that is deleted after the method returns, so you will need to make a copy of the data if you want to keep it. You can use the function copy-automation-value to do this. (Copying is done automatically when setting a property.)

Similarly, if an argument is an interface (such as <class-factory> or <LPDISPATCH>) you must call AddRef on it if it will be kept for use after the call returns, and later call Release when finished with it.

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OLE, COM, ActiveX and DBMS Reference - 31 MAR 2000