我正在尝试在类定义之外编写用于重载运算符“>>”和“<>

1>Source.obj : error LNK2019: unresolved external symbol "class std::basic_istream<char,struct std::char_traits<char> > & __cdecl operator>>(class std::basic_istream<char,struct std::char_traits<char> > &,class MyClass<int> &)" (??5@YAAAV?$basic_istream@DU?$char_traits@D@std@@@std@@AAV01@AAV?$MyClass@H@@@Z) referenced in function _main
1>Source.obj : error LNK2019: unresolved external symbol "class std::basic_ostream<char,struct std::char_traits<char> > & __cdecl operator<<(class std::basic_ostream<char,struct std::char_traits<char> > &,class MyClass<int>)" (??6@YAAAV?$basic_ostream@DU?$char_traits@D@std@@@std@@AAV01@V?$MyClass@H@@@Z) referenced in function _main
1>Source.obj : error LNK2019: unresolved external symbol "class std::basic_istream<char,struct std::char_traits<char> > & __cdecl operator>>(class std::basic_istream<char,struct std::char_traits<char> > &,class MyClass<class std::basic_string<char,struct std::char_traits<char>,class std::allocator<char> > > &)" (??5@YAAAV?$basic_istream@DU?$char_traits@D@std@@@std@@AAV01@AAV?$MyClass@V?$basic_string@DU?$char_traits@D@std@@V?$allocator@D@2@@std@@@@@Z) referenced in function _main
1>Source.obj : error LNK2019: unresolved external symbol "class std::basic_ostream<char,struct std::char_traits<char> > & __cdecl operator<<(class std::basic_ostream<char,struct std::char_traits<char> > &,class MyClass<class std::basic_string<char,struct std::char_traits<char>,class std::allocator<char> > >)" (??6@YAAAV?$basic_ostream@DU?$char_traits@D@std@@@std@@AAV01@V?$MyClass@V?$basic_string@DU?$char_traits@D@std@@V?$allocator@D@2@@std@@@@@Z) referenced in function _main

我一直在这个问题上上下求索。奇怪的是，如果我在类定义中写下它们的定义，它就可以完美运行。

#include <iostream>
#include <string>
using namespace std;

template <class MYTYPE>
class MyClass {
    MYTYPE *myVector;
    int dim;
    string name;
public:
    MyClass(int, string);
    MyClass() {};
    friend istream& operator>>(istream&, MyClass<MYTYPE>&);
    friend ostream& operator<<(ostream&, MyClass<MYTYPE>);
};

template <class MYTYPE>
MyClass<MYTYPE>::MyClass(int x, string y) {
    dim = x;
    name = y;
    myVector = new MYTYPE[dim];
}


template <class MYTYPE>
istream& operator>>(istream& X, MyClass<MYTYPE>& a){
    cout<<"Reading vector: "<<a.name<<endl;
    for(int indice = 0; indice < a.dim; indice++){
        cout<<a.name<<'['<<indice<<"]= ";
        X >> a.myVector[indice];
    }
    return X;
}

template <class MYTYPE>
ostream& operator<<(ostream& X, MyClass<MYTYPE> a){
    X<<"Vector: "<<a.name<<endl;
    for(int indice = 0; indice < a.dim; indice++)
        X<<a.myVector[indice]<<' ';
        X<<endl;
    return X;
}


int main() {
    MyClass<int> object(4, "Ints vector");
    MyClass<string> object2(5, "String vector");
    cin >> object;
    cin >> object2;
    cout << object;
    cout << object2;
    system("pause");
    return 0;
}

最佳答案

在您的代码中，MyClass 中友元运算符的声明应如下所示:

template<typename T> friend istream& operator>>(istream&, MyClass<T>&);
template<typename T> friend ostream& operator<<(ostream&, MyClass<T>);

也就是说，他们应该有自己的模板参数。

MyClass 的有效定义如下:

template <class MYTYPE>
class MyClass { 
    MYTYPE *myVector;
    int dim;
    string name;
public:
    MyClass(int, string);
    MyClass() {}

    template<typename T>
    friend istream& operator>>(istream&, MyClass<T>&);

    template<typename T>
    friend ostream& operator<<(ostream&, MyClass<T>);
};

关于c++ - 在模板类中为 >> 和 << 运算符实现重载，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/44709815/