ArcGIS Engine Developer Guide

VISUAL C++
removal would result in a serious corruption of the registry. InprocServer32 is the
standard COM mechanism that relates a component GUID to a DLL file; ATL
will insert the correct module name using the %MODULE% variable. Other
entries under the GUID specify the ProgID, threading model, and type library to
use with this component.
If the GUID of a component is changed during
development or the type library name is
changed, then it is important to keep the .rgs
content consistent with these changes. Otherwise,
the registry will be incorrect and object
creation can fail.
To register a COM coclass into a component category, there are two approaches.
The recommended approach is illustrated above: place GUIDs for component
categories beneath an Implemented Categories key, which in turn is under the
GUID of the coclass. The second approach is to use ATL macros in an objects
header file: BEGIN_CATEGORY_MAP, IMPLEMENTED_CATEGORY, or
END_CATEGORY_MAP. However, these macros do not correctly remove
registry entries as explained in the Microsoft Developer Network (MSDN) article
Q279459 BUG: ‘Component Category Registry Entries Not Removed in ATL
Component’. A header file is supplied with the GUIDs of all the component
categories used by ArcGIS; this is available in \Program
Files\ArcGIS\include\CatIDs\ArcCATIDs.h.
Debugging ATL code
In addition to the standard Visual Studio facilities, ATL provides a number of
debugging options with specific support for debugging COM objects. The output
of these debugging options is displayed in the Visual C++ Output window. The
QueryInterface call can be debugged by setting the symbol _ATL_DEBUG_QI,
AddRef, and Release calls with the symbol _ATL_DEBUG_INTERFACES, and
leaked objects can be traced by monitoring the list of leaked interfaces at termination
time when the _ATL_DEBUG_INTERFACES symbol is defined. The
leaked interfaces list has entries like the following:
INTERFACE LEAK: RefCount = 1, MaxRefCount = 3, {Allocation = 10}
On its own, this does not tell you much apart from the fact that one of your
objects is leaking because an interface pointer has not been released. However,
the Allocation number allows you to automatically break when that interface is
obtained by setting the m_nIndexBreakAt member of the CComModule at server
startup. This in turn calls the function DebugBreak to force the execution of the
code to stop at the relevant place in the debugger. For this to work, the program
flow must be the same.
extern "C"
BOOL WINAPI DllMain(HINSTANCE hInstance, DWORD dwReason, LPVOID /
*lpReserved*/)
{
if (dwReason == DLL_PROCESS_ATTACH)
{
_Module.Init(ObjectMap, hInstance, &LIBID_HISTORYLib);
DisableThreadLibraryCalls(hInstance);
_Module.m_nIndexBreakAt = 10;
}
else if (dwReason == DLL_PROCESS_DETACH)
{
_Module.Term();
}
104 • ArcGIS Engine Developer Guide