全局对象在程序进入main之前construct， 离开main后destruct

Solve  Bjarne Stroustrup's little puzzle:

Given the program:

#include<iostream.h>// DON'T use <iostream> or using namespace std;


main() {
    cout <<"Hello world" <<endl;
}

modify it to produce the output:
Initialize
Hello world
Clean up

ps: Do not change the function main() in any way. and only modify this cpp file.

Answer: 利用全局对象在程序进入main之前construct， 离开main后destruct之特点

#include<iostream.h>// DON'T use <iostream> or using namespace std;
class A {
public:
    A() { cout<<"Initialize: " <<endl; }
    ~A(){ cout<<"Clean up " <<endl;}
};
A test;   //建立一个全局对象，调用 A::A()
main() {
    cout <<"Hello world" <<endl;
}

// 析构： 调用A::~()

对于C程序通过设置函数属性为constuctor, 可使其在main()之前运行：

#include<stdio.h>
void first() __attribute__((constructor));
void first()
{
        printf("this is function %s/n",__FUNCTION__);
        return;
}
int main(int argc,char **argv)
{
        printf("this is function %s/n",__FUNCTION__);
        return 0;
}

运行结果：

this is function first
this is function main
this is function main