为什么用memset（）初始化sigint变量有助于防止Seg Fault？

背景：

struct sigaction用于为处理中断的小型C程序设置处理程序。完成第二个处理程序的实现后，当我收到“分段错误（内核已转储）”错误消息时，出现了问题。我完全以相同的方式设置了两个处理程序。在不初始化sigaction结构的情况下，第一个中断处理程序工作正常，但是，当我完成第二个处理程序的实现时，我收到了seg fault错误。

题：

为什么用memset（）初始化sigaction结构有助于修复错误？

码：

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <time.h>
#include <signal.h>
#include <string.h>

#define ALARMSECONDS    3
int numSigints = 5;

/* Handler function that prints out the current time on a SIGALRM interrupt. */
static void hdl(int signum)
{
    time_t currTime;
    time(&currTime);
    printf("\ncurrent time is %s", ctime(&currTime));
    alarm(ALARMSECONDS);//re-arm the alarm

}

/* Handler function that captures SIGINT interrupts 5 times before 
   actually exiting. Makes use of global variable to keep track of
   number of times the interrupt was sent.
 */
static void sigint_hdl(int signum)
{

    numSigints -= 1;    

    if(numSigints == 0)
    {
      printf("\nFinal Control-c caught. Exiting.\n");
      exit(1);
    } 
    else
    {
      printf("\nControl-c caught. %d more before program is ended.\n", 
        numSigints);
    }   
}

/* Periodically prints out the current time in Unix date format using 
   sigaction interrupt handling.   
*/
int main(int argc, char *argv[])
{

    //
    // vars
    //
    struct sigaction act;
    struct sigaction sigint_act;

    memset(&act, '\0', sizeof(act));//TODO Why does this fix SEGFAULT???

    //
    // intro
    //
    printf("Date will be printed every 3 seconds.\n");
    printf("Enter ^C 5 times to end the program.\n");

    //
    // set alarm to go off in 3 seconds
    //
    alarm(ALARMSECONDS);

    //
    // set handler of the sigaction to 'hdl' function defined above
    //
    act.sa_handler = hdl;
    sigint_act.sa_handler = sigint_hdl;

    //
    // activate sigaction
    //
    if(sigaction(SIGALRM, &act, NULL) < 0)
    {
      perror("sigaction -- SIGALRM");
      return 1;
    }

    if(sigaction(SIGINT, &sigint_act, NULL) < 0)
    {
      perror("sigaction -- SIGINT");
      return 1;
    }

    //
    // infinite loop
    //
    while(1) {
    }

    return 0;
}