C++编译错误;流操作符过载

Question

我正在学习C++流操作符重载。无法在Visual Studio中进行编译。

在istream&运算符部分中，编译器突出显示紧接在ins之后的克拉，并表示no operator >> matches these operands。

有人可以快速运行它，并告诉我什么是错的？

***************** 

// CoutCinOverload.cpp : Defines the entry point for the console application. 
// 

#include "stdafx.h" 
#include <iostream> 
#include <fstream> 
using namespace std; 

class TestClass { 

friend istream& operator >> (istream& ins, const TestClass& inObj); 

friend ostream& operator << (ostream& outs, const TestClass& inObj); 

public: 
    TestClass(); 
    TestClass(int v1, int v2); 
    void showData(); 
    void output(ostream& outs); 
private: 
    int variable1; 
    int variable2; 
}; 

int main() 
{ 
    TestClass obj1(1, 3), obj2 ; 
    cout << "Enter the two variables for obj2: " << endl; 
    cin >> obj2; // uses >> overload 
    cout << "obj1 values:" << endl; 
    obj1.showData(); 
    obj1.output(cout); 
    cout << "obj1 from overloaded carats: " << obj1 << endl; 
    cout << "obj2 values:" << endl; 
    obj2.showData(); 
    obj2.output(cout); 
    cout << "obj2 from overloaded carats: " << obj2 << endl; 

    char hold; 
    cin >> hold; 
    return 0; 
} 

TestClass::TestClass() : variable1(0), variable2(0) 
{ 
} 

TestClass::TestClass(int v1, int v2) 
{ 
    variable1 = v1; 
    variable2 = v2; 
} 

void TestClass::showData() 
{ 
    cout << "variable1 is " << variable1 << endl; 
    cout << "variable2 is " << variable2 << endl; 
} 

istream& operator >> (istream& ins, const TestClass& inObj) 
{ 
    ins >> inObj.variable1 >> inObj.variable2; 
    return ins; 
} 

ostream& operator << (ostream& outs, const TestClass& inObj) 
{ 
    outs << "var1=" << inObj.variable1 << " var2=" << inObj.variable2 << endl; 
    return outs; 
} 

void TestClass::output(ostream& outs) 
{ 
    outs << "var1 and var2 are " << variable1 << " " << variable2 << endl; 
} 

Answer 1

operator >>()应采取TestClass&而不是const TestClass&作为其第二个参数，因为你预期，同时从istream读来修改参数。

Answer 2

您应该更改参数类型inObj以引用非常量，因为它应该在operator>>中修改。你不能在const对象上修改，所以你不能在const对象（及其成员）上调用opeartor>>，这就是编译器的抱怨。

friend istream& operator >> (istream& ins, TestClass& inObj); 

Answer 3

取下标识const

friend istream& operator >> (istream& ins, const TestClass& inObj); 
              ^^^^^ 

你不能改变一个常量对象。