c++ 局部变量全局变量 atexit注册函数析构顺序

喜欢ヅ旅行 2021-11-13 15:46 241阅读 0赞

析构先后顺序为：局部变量、mian函数中注册atexit函数、全局变量及在其中注册atexit函数（全局变量和在全局变量中注册atexit函数析构顺序与构造顺序相反）。测试代码如下（gcc-4.6.3编译， ubuntu 12.04 linux 内核3.2.0运行）：

#include <cstdio>
    #include <cstdlib>
    #include <string>
    #include <ctime>
    
    static void PrintCurTime()
    {
    	clock_t t = clock();
    	printf("past seconds %d\n", t);
    }
    
    static void exit_0()
    {
    	printf("exit_0\n");
    }
    
    static void exit_1()
    {
    	printf("exit_1\n");
    }
    
    class A
    {
    public:
    	A(const char* name)
    	{
    		m_name = name;
    		printf("A::A() %s\n", m_name);
    	}
    	~A()
    	{
    		printf("A::~A() %s\n", m_name);
    		double sum = 0;
    		const int n = 1<<28;
    		for (int i = 0; i < n; ++i)
    		  sum += i*i;
    	}
    
    	const char* m_name;
    };
    
    class B
    {
    public:
    	B(const char* name)
    	{
    		m_name = name;
    		printf("B::B() %s\n", m_name);
    		atexit(exit_0);
    	}
    	~B(){printf("B::~B() %s\n", m_name);}
    
    	const char* m_name;
    };
    
    void FunInMain()
    {
    	A a("a_FunInMain");
    }
    
    B g_b("g_b");
    A g_a("g_a");
    
    int main(int argc, char* argv[])
    {
    	printf("enter main");
    
    	atexit(PrintCurTime);
    
    	atexit(exit_0);
    
    	A a1("a1");
    
    	FunInMain();
    
    	atexit(exit_1);
    
    	A a2("a2");
    
    	printf("exit main");
    
    	return 0;
    }

运行结果：

B::B() g\_b  
A::A() g\_a  
enter mainA::A() a1  
A::A() a\_FunInMain  
A::~A() a\_FunInMain  
A::A() a2  
exit mainA::~A() a2  
A::~A() a1  
exit\_1  
exit\_0  
past seconds 3810000  
A::~A() g\_a  
B::~B() g\_b  
exit\_0

将全局变量g\_b和g\_a声明顺序颠倒，运行结果：

A::A() g\_a  
B::B() g\_b  
enter mainA::A() a1  
A::A() a\_FunInMain  
A::~A() a\_FunInMain  
A::A() a2  
exit mainA::~A() a2  
A::~A() a1  
exit\_1  
exit\_0  
past seconds 3810000  
B::~B() g\_b  
exit\_0  
A::~A() g\_a