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[英]Why can't I change a private member of a class from a friend class in a different namespace?
[英]Can't change the value of private member of a class using friend class
所以我試圖學習如何使用朋友類更改私有類成員的值,但是朋友類無法更改主類的值,這是我所做的代碼,我是編碼世界的新手,請幫幫我:)
#include <iostream>
using namespace std;
class A {
private:
int marks;
public:
show_marks()
{
cout <<marks;
}
set_marks( int num )
{
marks =num;
}
friend class B;
};
class B{
public:
show_A_marks(A teacher, int num){
teacher.marks= num;
}
};
int main(){
A teacher;
teacher.set_marks(10);
teacher.show_marks();
cout <<endl;
B student;
student.show_A_marks(teacher,20);
teacher.show_marks();
}
- 這應該打印: 10 20 但正在打印: 10 10
在函數中:
show_A_marks(A teacher, int num)
您正在按價值傳遞teacher
。 您正在制作該值的副本,並編輯該副本。 當函數返回時,副本消失了。 您需要通過引用傳遞它:
show_A_marks(A& teacher, int num)
// ^ reference to A
請參閱按引用傳遞與按值傳遞之間的區別是什么? 了解更多信息。
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