Handling Errors in Visual C++

In COM, most operations return an HRESULT return code that indicates whether a function completed successfully. The #import directive generates wrapper code around each "raw" method or property and checks the returned HRESULT. If the HRESULT indicates failure, the wrapper code throws a COM error by calling _com_issue_errorex() with the HRESULT return code as an argument. COM error objects can be caught in a try-catch block. (For efficiency's sake, catch a reference to a _com_error object.)

Remember, these are ADO errors: they result from the ADO operation failing. Errors returned by the underlying provider appear as Error objects in the Connection object's Errors collection.

The #import directive only creates error-handling routines for methods and properties declared in the ADO .dll. However, you can take advantage of this same error-handling mechanism by writing your own error-checking macro or inline function. See the topic Visual C++ Extensions for examples.