c++ - 错误 : 'member' is private within this context - namespace

Question

我在命名空间中有一个类，如下所示。测试.h

#include <iostream>
using std::cout;
namespace n1
{
    class myClass;
}

class n1::myClass
{
public:
    myClass(int na, int nb):a(na), b(nb){}
private:
    int a;
    int b;
friend std::ostream& operator << (std::ostream & stream, const n1::myClass& cls);
};

测试.cpp

#include "test.h"
std::ostream& operator << (std::ostream & str, const n1::myClass& cls)
{
    str << cls.a << " " << cls.b << std::endl;
}

在编译时，出现以下错误。

test.h: In function ‘std::ostream& operator<<(std::ostream&, const n1::myClass&)’:
test.h:13:6: error: ‘int n1::myClass::a’ is private
test.cpp:5:13: error: within this context
test.h:14:6: error: ‘int n1::myClass::b’ is private
test.cpp:5:29: error: within this context

如何克服错误？

Answer 1

您可以定义运算符 <<在 myClass 的命名空间内定义:

namespace n1
{
 std::ostream& operator << (std::ostream & str, const myClass& cls)
 {
    str << cls.a << " " << cls.b << std::endl;
 }
}

因为你答应过myClass在 namespace 中有一个 friend n1但实际上您在全局 namespace 中声明了运算符。