C++使用[]赋值

Posted 2022-05-27 shuiyonglewodezzzzz

class Test 

public:
    const int& operator[]( const int& index) 
    
        std::cout << "[]" << std::endl;
        return 2;
    
    int& operator[]( int&& index)
    
        std::cout << "[][]" << std::endl;
        int j = 3;
        return j;
    
    const int& operator=(const int& index) 
    
        std::cout << "=" << std::endl;
        return 3;
    
    friend std::ostream& operator<<(std::ostream& out, const Test&)
    
        out <<1 << endl;
        return out;
    
;
int main () 

    Test t;
    const int i = 12;
    int k = t[1] = i;
    cout << k << endl;
    cout << t[i] << endl;
  return 0;
 

代码：

t[1] = i;

会调用参数为int && 的[]重载函数，也就是

int& operator[](int&& index)
    
        std::cout << "[][]" << std::endl;
        int j = 3;
        return j;
    

注意此函数不能返回const int&，因为不能给一个const赋值。

这句话的含义是 先t[1]，然后赋值i