多文件组织 问题
//hello.h#ifndef Hello_HH#define Hello_HHvoid HelloWorld(); #endif//HelloWorld.cpp#include <iostream>#include "hello.h"using namespace std;void HelloWorld(){ cout<<"yes,Hello World"<<endl;}//main.cpp#include <iostream>#include "hello.h"using namespace std;int main(){ cout<<"Before hello world!"<<endl; HelloWorld(); cout<<"After hello world"<<endl; return 0;}//hello.h#ifndef Hello_HH#define Hello_HHextern void HelloWorld();//这也该一下 #endif