c++ - 错误 : passing 'const …' as 'this' argument of '…' discards qualifiers in calling method

Question

我将一个对象的引用传递给一个函数，我使用 const 来指示它是只读方法，但是如果我在该方法内部调用另一个方法，即使我没有传递引用作为参数。

error: passing 'const A' as 'this' argument of 'void A::hello()' discards qualifiers [-fpermissive]

error: passing 'const A' as 'this' argument of 'void A::world()' discards qualifiers [-fpermissive]

#include <iostream>

class A
{
public:
    void sayhi() const
    {
        hello();
        world();
    }

    void hello()
    {
        std::cout << "world" << std::endl;
    }

    void world()
    {
        std::cout << "world" << std::endl;
    }
};

class B
{
public:
    void receive(const A& a) {
        a.sayhi();
    }
};

class C
{
public:
    void receive(const A& a) {
        B b;
        b.receive(a);
    }
};

int main(int argc, char ** argv)
{
    A a;
    C c;
    c.receive(a);

    return 0;
}

Answer 1

既然sayhi()是const，那么它调用的所有函数也必须声明为const，在本例中是hello( ) 和 world()。您的编译器警告您 const-correctness .