#include<iostream> using namespace std; class student; class teacher { public : student *p; teacher(int x); int A; ~teacher(); }; teacher::teacher(int x) { A = x; p = new student(8); } teacher::~teacher() { delete p; } class student { friend class teacher; public: int a = 10; student(int x); }; student::student(int x) { a = x; } void func() { student s(100); cout << s.a << endl; teacher t(1); cout << t.A << endl; cout << t.p->a << endl; } int main() { func(); system("pause"); return 0; }这个代码问题出现在哪，该怎么解决

这段代码存在一个循环包含的问题，即 `class teacher` 中的 `student *p` 指针指向了 `class student`，而 `class student` 中又要使用 `class teacher`，这就导致了编译器无法处理两个类的定义顺序。要解决这个问题，可以将 `class student` 的定义放在 `class teacher` 的前面，或者使用前置声明来解决。修正后的代码如下：

#include<iostream> 
using namespace std; 

class student;

class teacher  { 
public: 
    student *p; 
    teacher(int x); 
    int A; 
    ~teacher(); 
};

class student { 
    friend class teacher; 
public:  
    int a = 10; 
    student(int x); 
};

student::student(int x) { 
    a = x; 
} 

teacher::teacher(int x) { 
    A = x; 
    p = new student(8); 
} 

teacher::~teacher() { 
    delete p; 
}    

void func() { 
    student s(100); 
    cout << s.a << endl; 
    teacher t(1); 
    cout << t.A << endl; 
    cout << t.p->a << endl; 
} 

int main() { 
    func(); 
    system("pause"); 
    return 0; 
}