C++一道面試題（atexit）

題：main主函數執行完畢後，是是否可能會再執行一段代碼？給出說明。

答：如果需要加入一段在main退出後執行的代碼，可以使用atexit()函數註冊一個函數，代碼如下：

#include <stdio.h>
#include <stdlib.h>

int atexit(void(*function)(void));
void fn1(void),fn2(void),fn3(void),fn4(void);

int main()
{
    atexit(fn1);
    atexit(fn2);
    atexit(fn3);
    atexit(fn4);
    printf("This is executed first.\n");

    return 0;
}

void fn1()
{
    printf(" next.\n");
}

void fn2()
{
    printf(" executed ");
}

void fn3()
{
    printf(" is");
}

void fn4()
{
    printf("This");
}

執行結果：

This is executed first.
This is executed next.

說明：

（1）函數原型：int atexit( void ( __cdecl *func )( void ) );

（2）The atexit function is passed the address of a function (func) to be called when the program   terminates normally. Successive calls to atexit create a register of functions that are executed in LIFO (last-in-first-out) order. The functions passed to atexit cannot take parameters. atexit and _onexit use the heap to hold the register of functions. Thus, the number of functions that can be registered is limited only by heap memory.