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Creating Truly Maintainable Class Factories

November 2000/Creating Truly Maintainable Class Factories/Listing 1

Listing 1: A macro to define a factory function in a DLL

Tells the compiler to export a function
on _WIN32 platform.
#ifdef _WIN32
  #define DLLFUNC __declspec( dllexport )
#elif defined( _GNU_C )
  #define DLLFUNC
  #error Unsupported Platform.  Please port me.

Tells the compiler which "calling convention"
to use.
#ifdef _WIN32
  #define DLLCALL __stdcall
#elif defined( _GNU_C )
  #define DLLCALL
  #error Unsupported Platform.  Please port me.

#define EXTERNC extern "C"

 Creates an entry in the DLL function export table
 for a factory-compatible class instantiation routine.

 * base      - type of class the factory expects.
 * the_class - type of class the classid corresponds to.
 * prefix    - function name prefix.  Can be used to allow
               multiple factories access to the same DLL.
 * classid   - class identifier.
#define FACTORYFUNC( base , the_class , prefix , classid ) \
  EXTERNC DLLFUNC base* DLLCALL prefix##classid( void )    \
    { return new the_class; } 

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