late to object layout. Because all member functions in COM interface definitions are pure virtual, the derived class must provide an implementation of every method that is present in any of its interfaces. Methods that are common to two or more interfaces (e.g., Querylnterface, AddRef, etc.) need to be implemented only once, 3 Which was highly inspired by a discussion between the author and Tye McQueen during a COM seminar. object, uuid(DF12E155-A29A-lldO-8C2D-0080C73925BA)] interface IOldPug : IPug { HRESULT SnoreLoudly(void); }

Essential Communications Executive Coaching Los Angeles - Essential Communications

The term execution context is used by the COM specification to describe what has since been renamed an apartment. An apartment is neither a thread nor a process; however, it shares common attributes with both. Apartments are fully described in Chapter 5. Note that all but one of the entry points into the FastSt ri ng DLL are virtual functions. The virtual functions of the interface class are always called indirectly via a function pointer stored in a vtbl, without requiring the client to link against their symbolic names at development time. This means that the interface methods are immune to symbolic mangling differences between compilers. The only entry point that is explicitly linked against by name is CreateFastStri ng, the global function that bootstraps the client into the world of FastStri ng. Note, however, that this function was exported using extern "C", which suppresses symbolic mangling. This implies that all C++ compilers expect the import library and DLL to export the same symbol. The net result of using this technique is that one can safely expose a class from a DLL using one C++ environment and access the class from any other C++ development environment. This capability is critical for building a vendorneutral substrate for reusable components.COM does impose one limitation on interface inheritance: COM interfaces cannot derive directly from more than one interface. The following is not legal in COM: If the object presented to this function is both lCat and lPug compatible, then both functionalities are exploited. If the object is not in fact lCat or lPug compatible, then this particular function simply ignores the missing aspect(s) of the object. The following is the semantically equivalent version using Que rylnte rface: void TryToSnoreAndlgnore(/* [in] *1 lUnknown *pUnk) { HRESULT hr; lPug ''(pPug = 0; hr = pUnk->Querylnterface(llD_lPug, (void**)&pPug); if (SUCCEEDED(hr)) {II the object is Pug-compatible pPug->Snore(); pPug->Release(); II R2 } With these two modifications in place, the corresponding client code now becomes much more uniform and unambiguous: define END_INTERFACE_TABLE() \ { 0, 0, 0 } }; return table; } All that is required is a routine tha class FastString : public IFastString, public IPersistentObject { int m_cPtrs; II count of outstanding ptrs public: II initialize pointer count to zero FastString(const char *psz) : m_cPtrs(O) {} void DuplicatePointer(void) { II note duplication of pointer ++m_cPtrs; }

Essential Mod | Download - The Mod You Need For Minecraft Java Essential Mod | Download - The Mod You Need For Minecraft Java

define SUCCEEDED(hr) (long(hr) >= 0) #define FAILED(hr) (long(hr) < 0) These two macros take advantage of the fact that the severity bit is also the sign bit when treating an HRESULT as a signed integer. The SDK headers contain the definitions of all standard HRESULTs. These HRESULTs have symbolic names that correspond to the three components of an HRESULT using the following format: generated type library as documentation for the enumeration. If one ignores the attributes in an IDL file, the syntax is simply that of C. IDL supports structures, unions, arrays, enumerations, and typedefs with a syntax identical to that of their C counterparts. When defining COM methods in IDL, one needs to indicate explicitly whether the caller or the callee will be writing or reading each method parameter. This is accomplished using the parameter attributes [i n] and [out]: IFastString* CreateFastString(const char *psz) { IFastString *pfsResult = new FastString(psz); if (pfsResul t) pfsResult->DuplicatePointer(); return pfsResult; }

Licenses

Recent issues of C++ Report are available at http://www.develop.comJdbox/cxx/lnterfacePtr.htm and http://www.develop.comJdbox/cxx/SmartPtr.htm.

Essentials clothing for Men | SSENSE UK Fear Of God Essentials clothing for Men | SSENSE UK

IUnknown The COM interface IUnknown serves the same purpose as the IExtensi bl eObject interface defined in the previous chapter. The following is the final version of IExtensi bl eObject that appeared at the end of the chapter:Object Extensibility The techniques presented so far allow clients to select and load binary components dynamically that can evolve their implementation layout over time without requiring client recompilation. This by itself is extremely useful for building dynamically composable systems. However, one aspect of the object that cannot evolve over time is its interface. This is because the client compiles lCat ''(pCat = 0; hr = pUnk->Querylnterface(llD_lCat, (void**)&pCat); if (SUCCEEDED(hr)) {II the object is Cat-compatible pCat->lgnoreMaster(); pCat->Release(); II R2 } } void TryToSnoreAndlgnore(/* [in] *1 lUnknown *pUnk) { lPug ~(PPug = 0; pPug = dynamic_cast (pUnk); if (pPug) II the object is Pug-compatible pPug->Snore(); lCat ''(pCat = 0; pCat = dynamic_cast (pUnk); if (pCat) II the object is Cat-compatible pCat->lgnoreMaster(); } extern "C" const 110 IIO_ICalculator; interface ICalculator : public IUnknown { virtual HRESULT STDMETHODCALLTYPE Clear(void) = 0; virtual HRESULT STDMETHODCALLTYPE Add(long n) = 0; virtual HRESULT STDMETHODCALLTYPE Sum(long *pn) =0; }