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