C语言中的pause()函数和alarm()函数以及sleep()函数

#include <unistd.h>

int pause(void);

#include <unistd.h>

unsigned int alarm(unsigned int seconds);

#include <unistd.h>
#include <signal.h>
void handler()
{
  printf("hello\n");
}

main()
{
  int i;
  signal(SIGALRM, handler);
  alarm(5);
  for(i = 1; i < 7; i++)
  {
    printf("sleep %d ...\n", i);
    sleep(1);
  }
}

sleep 1 ...
sleep 2 ...
sleep 3 ...
sleep 4 ...
sleep 5 ...hello
sleep 6 ...

 #include <unistd.h>

unsigned int sleep(unsigned int seconds);