代码如下：
#include <stdio.h>
#include <signal.h>
#include <errno.h>
/*static volatile atomic variable*/
static volatile sig_atomic_t sigflag = 0;
/*private signal control handler*/
static void TurnFlag(int no){
sigflag = (sigflag == 0) ? 1 : 0;
}
/**
* set signal handler
* if error return -1
* or return 0
*/
int InitHandler(int signo){ /*signal macro*/
/*using sigaction function need this struct*/
struct sigaction act;
act.sa_handler = TurnFlag; /*set signal function*/
act.sa_flags = 0;/*meaning sigaction is pure action*/
if( (sigemptyset(&act.sa_mask) == -1)