c++ - 重载运算符 '>>' 的使用不明确(操作数类型为 'istream'(又名 'basic_istream')和 'MyIncreEx')

Question

这是代码，我似乎没有发现它有什么问题；我需要重载 << 和 >> 运算符，但出现以下错误:

重载运算符“>>”的使用不明确(操作数类型为“istream”(又名“basic_istream”)和“MyIncreEx”)

我看不出它有什么模棱两可的地方:

class MyIncreEx;

istream& operator>>(istream& is, MyIncreEx& s);
ostream& operator<<(ostream &os, MyIncreEx& s);
MyIncreEx operator++(MyIncreEx& d, int dummy);
MyIncreEx operator++(MyIncreEx& d);

class MyIncreEx
{
    friend istream& operator>>(istream& is, MyIncreEx s);
    friend ostream& operator<<(ostream& os, MyIncreEx s);
    friend MyIncreEx operator++(MyIncreEx& d, int dummy);
    friend MyIncreEx operator++(MyIncreEx& d); 

public:
    int num1 = 0, num2 = 0, num3 = 0;
};

istream& operator>>(istream& is, MyIncreEx& s)
{
    is >> s.num1;
    is >> s.num2;
    is >> s.num3;
    return is;
};

ostream& operator<<(ostream &os, MyIncreEx& s)
{
    os << "(" << s.num1 <<"," <<s.num2 << "," << s.num3 <<")"<< endl;
    return os;
};

MyIncreEx operator++(MyIncreEx& d)              
{
    d.num1++;
    d.num2++;
    d.num3++;
    return d;
};

MyIncreEx operator++(MyIncreEx& d, int dummy) 
{
    d.num1++;
    d.num2++;
    d.num3++;
    return d;
};

int main()
{
    MyIncreEx obj;

    cout << "please enter three numbers: ";
    cin  >> obj;
    
    cout << "The original value are: " << obj << endl;
    obj++;
    
    cout << "The new values after obj++ are: " <<  obj << endl;
    ++obj;
    
    cout << "The new values after ++obj are: " << obj << endl;
}

Answer 1

您声明了两个不同版本的输出运算符:

istream& operator>>(istream& is, MyIncreEx& s);
ostream& operator<<(ostream &os, MyIncreEx& s);

class MyIncreEx
{
    friend istream& operator>>(istream& is, MyIncreEx s);
    friend ostream& operator<<(ostream& os, MyIncreEx s);
    ...
};

friend 运算符具有不同且相互冲突的签名。您可能想将它们声明为

    friend istream& operator>>(istream& is, MyIncreEx& s);
    friend ostream& operator<<(ostream& os, MyIncreEx const& s);

(假设您还修复了输出运算符以使用 MyIncreEx const& 而不是 MyIncreEx&)。