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Compiler Warning (level 4) C4339

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The latest version of this topic can be found at Compiler Warning (level 4) C4339.

type' : use of undefined type detected in WinRT or CLR meta-data - use of this type may lead to a runtime exception

A type was not defined in code that was compiled for Windows Runtime or the common language runtime. Define the type to avoid a possible runtime exception.

This warning is off by default. See Compiler Warnings That Are Off by Default for more information.

The following sample generates C4339 and shows how to fix it:

// C4339.cpp  
// compile with: /W4 /clr /c  
// C4339 expected  
#pragma warning(default : 4339)  
  
// Delete the following line to resolve.  
class A;  
  
// Uncomment the following line to resolve.  
// class A{};  
  
class X {  
public:  
   X() {}  
  
   virtual A *mf() {  
      return 0;  
   }  
};  
  
X * f() {  
   return new X();  
}