#ifndef……#define……#endif

//a.h#ifndef _A_H#define _A_Hclass A{pbulic:A(){}~A(){}}#endif// B.h#ifndef _B_H#define _B_H#include "a.h"class B : public A{public:B(){}~B(){}}#endif// C.h#ifndef _C_H#define _C_H#include "a.h"class C : public A{public:C(){}~C(){}}#endif// main.cpp#include "b.h"#include "c.h"int main(){B b;C c;return 0;}

 如果A.h中没有#ifndef ...则编译器会报错