好友ostream无法访问私人会员

Question

我也看到过类似的其他问题，但我没有得到解决方案。代码如下：

cout_overload.h:

#ifndef COUT_OVERLOAD_H_
#define COUT_OVERLOAD_H_

          #include <iostream>

          class A
          {
                  private:
                          int data;
                  public:
                          A(int d);
                          friend std::ostream & operator << 
                            (std::ostream os, const A &t );
          };

 #endif

cout_overload_r.cpp:

   #include <iostream>                                                                       
   #include "cout_overload.h"

   A::A(int d)
   {
           data = d;
   }

   std::ostream &operator << (std::ostream &os, const A&t)
   {
          os << " t = " << t.data ;
          return os;
   }

main.cpp:

#include <iostream>                                                                        #include "cout_overload.h"

 int main(void)
  {
          A ra(1);
          using std::cout;

  //      cout<<ra;

         return 0;
 }

编译时报错：

Answer 1

您需要修改 friend 函数并在

中使用 ostream&

friend std::ostream & operator << (std::ostream os, const A &t );

并替换上面的行，

friend std::ostream & operator << (std::ostream &os, const A &t );

因为ostream是一个输出流，所以&是通过引用传递（将流传递给函数的唯一方法）..

好友ostream无法访问私人会员

Friend ostream can't access private member

c++

iostream

operator-overloading