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Compiler Warning (level 4) C4512

'class' : assignment operator could not be generated

The compiler cannot generate an assignment operator for the given class. No assignment operator was created.

An assignment operator for the base class that is not accessible by the derived class can cause this warning.

To avoid this warning, specify a user-defined assignment operator for the class.

The compiler will also generate an assignment operator function for a class that does not define one. This assignment operator is a memberwise copy of the data members of an object. Because const data items cannot be modified after initialization, if the class contains a const item, the default assignment operator would not work. Another cause of the C4512 warning is a declaration of a nonstatic data member of reference type. If the intent is to create a non-copyable type, you must also prevent the creation of a default copy constructor.

You can resolve the C4512 warning for your code in one of three ways:

  • Explicitly define an assignment operator for the class.

  • Remove const or the reference operator from the data item in the class.

  • Use the #pragma warning statement to suppress the warning.

The following sample generates C4512.

// C4512.cpp
// compile with: /EHsc /W4
// processor: x86

class Base {
   const int a;

   Base(int val = 0) : a(val) {}
   int get_a() { return a; }
};   // C4512 warning

class Base2 {
   const int a;

   Base2(int val = 0) : a(val) {}
   Base2 & operator=( const Base2 & ) { return *this; }
   int get_a() { return a; }

// Type designer intends this to be non-copyable because it has a 
// reference member
class Base3
   char& cr;
   Base3(char& r) : cr(r) {}
   // Uncomment the following line to explicitly disable copying:
   // Base3(const Base3&) = delete; 
};   // C4512 warning

int main() {
   Base first;
   Base second;

   // OK
   Base2 first2;
   Base2 second2;

   char c = 'x';
   Base3 first3(c);
   Base3 second3 = first3; // C2280 if no default copy ctor