C++定義類型轉換

Question

有沒有一種方法來定義從用戶定義的類到基元類型（int，short等）的類型轉換？另外，任何這樣的機制是否需要明確的轉換，還是會隱含起作用？

例如：

// simplified example class 
class MyNumberClass 
{ 
private: 
    int value; 
public: 
    // allows for implicit type casting/promotion from int to MyNumberClass 
    MyNumberClass(const int &ampv) 
    { 
     value = v; 
    } 
}; 

// defined already above 
MyNumberClass t = 5; 

// What's the method definition required to overload this? 
int b = t; // implicit cast, b=5. 
// What's the method definition required to overload this? 
int c = (int) t; // C-style explicit cast, c=5. 
// ... etc. for other cast types such as dynamic_cast, const_cast, etc. 

Answer 1

是的，你可以定義一個operator type()做轉換，是的，每當需要這樣的轉換，將隱含工作：

operator int() { 
    return value; 
}