Compiler Error C3203

 

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'type' : unspecialized class template or generic can't be used as a template or generic argument for template or generic parameter 'param', expected a real type

You passed an invalid argument to a class template or generic. The class template or generic expects a type as a parameter.

This error can be generated as a result of compiler conformance work that was done for Visual C++ 2005: an unspecialized class template can't be used as a template argument in a base class list. To resolve C3203, explicitly add the template type parameter(s) to the template class name when using it as a template parameter in a base class list.

// C3203.cpp  
template< typename T >  
struct X {  
   void f(X) {}  
};  
  
template< typename T >  
struct Y : public X<Y> {   // C3203  
// try the following line instead  
// struct Y : public X<Y<T> > {  
   void f(Y) {}  
};  
  
int main() {  
   Y<int> y;  
}  

The following sample generates C3203 and shows how to fix it:

// C3203_b.cpp  
// compile with: /c  
template <class T>  
struct S1 {};  
  
template <class T>  
class C1 {};  
  
typedef C1<S1> MyC1;   // C3203  
  
// OK  
template <template <class> class T>  
class C2 {};  
  
typedef C2<S1> MyC1;  
  
template <class T>  
class C3 {};  
  
typedef C3<S1<int> > MyC12;  

C3203 can also occur when using generics:

// C3203_c.cpp  
// compile with: /clr /c  
generic <class T>  
value struct GS1 {};  
  
generic <class T>  
value struct GC1 {};  
  
typedef GC1<GS1> MyGC1;   // C3203  
typedef GC1<GS1<int> > MyGC2;   // OK  

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