main 主函数执行完毕后，是否可能会再执行一段代码?

在网上看到朗讯的一道笔试题,题目是这样的:

main 主函数执行完毕后，是否可能会再执行一段代码，给出说明？

答案：可以，可以用_onexit 注册一个函数，它会在main 之后执行
int fn1(void), fn2(void), fn3(void), fn4 (void);

#include<iostream>
#include<cstdio>
#include<string>
using namespace std;
int main( void )
{ freopen("out.txt","w",stdout);
int fn1();
int fn2();
int fn3();
int fn4();
string str("zhanglin");
/*
The _onexit function is passed the address of a
function (func) to be called when the program
terminates normally. Successive calls to _onexit create
a register of functions that are executed in LIFO (last-in-first-out)
order. The functions passed to _onexit cannot take parameters.

*/
_onexit( fn1 );
_onexit( fn2 );
_onexit( fn3 );
_onexit( fn4 );
printf( "This is executed first./n" );
//system("PAUSE");
return 0;
}
int fn1()
{
printf( "next./n" );
return 0;
}
int fn2()
{
printf( "executed " );
return 0;
}
int fn3()
{
printf( "is " );
return 0;
}
int fn4()
{
printf( "This " );

return 0;

}