C++重寫/過載問題

Question

我在C++中面臨的一個問題：

#include <iostream> 

class A 
{ 
protected: 
    void some_func(const unsigned int& param1) 
    { 
    std::cout << "A::some_func(" << param1 << ")" << std::endl; 
    } 
public: 
    virtual ~A() {} 
    virtual void some_func(const unsigned int& param1, const char*) 
    { 
    some_func(param1); 
    } 
}; 

class B : public A 
{ 
public: 
    virtual ~B() {} 
    virtual void some_func(const unsigned int& param1, const char*) 
    { 
    some_func(param1); 
    } 
}; 

int main(int, char**) 
{ 
    A* t = new B(); 
    t->some_func(21, "some char*"); 
    return 0; 
} 

我用G ++ 4.0.1編譯錯誤：

$ g++ -W -Wall -Werror test.cc 
test.cc: In member function ‘virtual void B::some_func(const unsigned int&, const char*)’: 
test.cc:24: error: no matching function for call to ‘B::some_func(const unsigned int&)’ 
test.cc:22: note: candidates are: virtual void B::some_func(const unsigned int&, const char*) 

爲什麼我必須指定類B中some_func（param1）的調用是A :: some_func（param1）？它是一個g ++ bug還是來自g ++的隨機消息，以防止我看不到的特殊情況？

Answer 1

問題是，在派生類中，您將隱藏受保護的方法在基類中。你可以做幾件事，要麼你完全限定派生對象中的受保護方法，要麼使用using指令將該方法帶入範圍：

class B : public A 
{ 
protected: 
    using A::some_func; // bring A::some_func overloads into B 
public: 
    virtual ~B() {} 
    virtual void some_func(const unsigned int& param1, const char*) 
    { 
    A::some_func(param1); // or fully qualify the call 
    } 
};