GUID Maps

Stingray Foundation Library User's Guide

3.3 GUID Maps

Implementing QueryGuid() is a tedious and repetitive task, so using macros to write most of the code is convenient. A GUID map is a set of macros that collectively implement the QueryGuid() function. They are nearly identical to ATL's BEGIN_COM_MAP and END_COM_MAP macros, which implement QueryInterface(). Example 4 shows how you can use GUID maps to implement QueryGuid().

Example 4: Using a GUID map

class CCow : public IAnimal
{
public:
  BEGIN_GUID_MAP(CCow)
    GUID_ENTRY(IAnimal)
    GUID_ENTRY(IQueryGuid)
  END_GUID_MAP
…
};

The macros expand out to the same implementation of CCow::QueryGuid() shown in the previous sample.

In certain cases, a class may inherit an interface from more than one base class. That will produce an ambiguous reference in the GUID map that you must resolve with the GUID_ENTRY2 macro. Example 5 shows the GUID_ENTRY2 macro used to resolve an ambiguous reference to IQueryGuid.

Example 5: Resolving an ambiguous reference in a GUID map

class IFood : public IQueryGuid
{
public:
  virtual void BeConsumed() = 0;
};

class CCow : public IAnimal, public IFood
{
public:
  BEGIN_GUID_MAP(CCow)
    GUID_ENTRY(IAnimal)
    GUID_ENTRY2(IQueryGuid, IAnimal)
  END_GUID_MAP
…
};

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