C++ 类模板

Question

我正试图让这些 C++ 中的类模板工作。但是总是有这个错误。重载有某种错误，但我不知道是什么。我已经尝试使用成员函数重载 << 运算符，但仍然存在错误。

#include <iostream>

using namespace std;

const int MAX = 10;
template <class T>
class mstack
{
    T stk[MAX];
    int top;

public:
    mstack()
    {
        top = -1;
    }

    void push(T data)
    {
        if(top==MAX-1)
        {
            cout << endl << "stack is full" << endl;
        }
        else
        {
            top++;
            stk[top] = data;
        }
    }

    T pop()
    {
        if (top==-1)
        {
            cout << endl << "stack is empty" << endl;
            return NULL;
        }
        else
        {
            T data = stk[top];
            top--;
            return data;
        }
    }
};

class mcomplex
{
    float img, real;

public:
    mcomplex()
    {
        real = 0;
        img = 0;
    }

    mcomplex(float r, float i)
    {
        real = r;
        img = i;
    }

    friend ostream& operator<< (ostream &o,mcomplex &c);
};

ostream& operator<< (ostream &o, mcomplex &c)
{
    o << c.real << "\t" << c.img;
    return o;
}

int main()
{
    mcomplex c1(1.5f,2.5f), c2(3.5f,4.5f), c3(-1.5f,-0.6f);
    mstack <mcomplex> s3;
    s3.push(c1);
    s3.push(c2);
    s3.push(c3);
    cout << endl << (s3.pop());
    cout << endl << s3.pop();
    cout << endl << s3.pop() << endl;
    return 0;
}

编译错误如下:

|76|error: no match for 'operator<<' (operand types are 'std::basic_ostream::__ostream_type {aka std::basic_ostream}' and 'mcomplex')

|62|note: candidate: std::ostream& operator<<(std::ostream&, mcomplex&)

|77|error: invalid initialization of non-const reference of type 'mcomplex&' from an rvalue of type 'mcomplex'

|78|error: no match for 'operator<<' (operand types are 'std::basic_ostream::__ostream_type {aka std::basic_ostream}' and 'mcomplex')

谁能告诉我这里的错误是什么？

Answer 1

您的 pop() 函数正在返回一个临时值。对该值进行非常量引用没有意义。