我的预增量工作正常但不是 post 增量

Question

我已经实现了以下 class 并尝试重载前置和 post-增量运算符以及提取“>>”运算符。程序在 'cout << ++num1;' 之前运行良好，但在最后一行 'cout << num1++;' 打印垃圾值。我不明白为什么预增量工作正常但不适用于 post-increment.

class ComplexNumber
{
private:
    float real;
    float img;
public:
    ComplexNumber();
    ComplexNumber(float, float);
    ComplexNumber(const ComplexNumber& cn);
    friend istream& operator>>(istream& in, ComplexNumber& cn);
    // cin >> complexNo1 >> complexNo2;
    friend ostream& operator<<(ostream& out, const ComplexNumber& cn);
    //cout << complexNo1 << complexNo2; //3+4i, 5+10i
    ComplexNumber& operator++(int);
    //post increment operator. complexNo++;
    ComplexNumber& operator++();
    //pre increment operator. ++complexNo;
ComplexNumber& ComplexNumber::operator++(int x) // postincrement
{
    ComplexNumber c = *this;
    ++(*this);
    return c;
}
ComplexNumber& ComplexNumber::operator++() // preincrement
{
    real++;
    img++;
    return *this;
}
int main()
{
    ComplexNumber num1;//,num2,num3
    cin >> num1;
    cout << "-------------------------------------------" << endl;
    cout << "Complex Number is : ";
    cout << num1;
    cout << ++num1;
    cout << num1++;
}

Answer 1

您的 post-increment 运算符是对本地对象的 returning 引用，该对象将在函数结束时被销毁，returned 引用始终悬空并取消引用它导致到 UB。

Post-增量运算符应该return-by-value，例如

ComplexNumber ComplexNumber::operator++(int x) // postincrement
{
    ComplexNumber c = *this;
    ++(*this);
    return c;
}

我的预增量工作正常但不是 post 增量

My pre increment is working fine but not the post increment

c++

overloading

class

function

operators