如何解決這個丟棄限定符錯誤？

Question

我想通過使用STL優先級隊列根據它們的優先級實現一系列雜事。當我嘗試編譯時，我收到了有關輸出函數的錯誤以及過載的運算符<。我試着讓函數爲const，但是這並沒有解決問題。我怎樣才能解決這個問題？

main.cc

priority_queue<Chore> chores; 
Chore tmp; 

for(int i = 5; i >0; i--) { 
    tmp.input(cin); 
    chores.push(tmp); 
} 

while(!chores.empty()) { 
    chores.top().output(); 
    chores.pop(); 
} 

return 0; 

}; 

chore.h

class Chore { 
    public: 
    Chore(); 
    void input(istream& ins); 
    void const output(); 
    bool const operator <(const Chore c1); 

    private: 
    string chore_name; 
    int priority; 
}; 

chore.cc

Chore:: Chore() { 
    chore_name = ""; 
    priority = 0; 
}; 

void Chore:: input(istream& ins) { 
    cout << "Please Enter the name of the chore: "; 
    cin >> chore_name; 
    cout << endl << "Please Enter The Priority Level: "; 
    cin >> priority; 
    cout << endl; 
}; 

void const Chore:: output() { 
    cout << "Chore: " << chore_name << endl; 
    cout << "Priority: " << priority << endl << endl; 
}; 

bool const Chore:: operator <(const Chore c1) { 
    return (priority < c1.priority); 
}; 

Answer 1

你最好不要讓成員函數常量。這樣做：

class Chore { 
    ... 
    void output() const; 
    bool operator<(const Chore& c1) const; //Also added pass by reference here 
}; 
void Chore::output() const {...} 
bool Chore::operator<(const Chore& c1) const {...}