C++(在 Linux 下)程序没有给出预期的输出(定时器)

Question

我有这个 C++ 程序。它有一个简单的 for 循环，打印从 1 到 20 的数字。在此期间，执行期间，计时器多次到期，每次到期时，它应该打印信号处理程序的输出。

不幸的是我没有得到这个输出。它只是简单地打印从 1 到 20 的数字。有人可以帮我吗？

提前致谢

#include <stdlib.h>
#include <unistd.h>
#include <stdio.h>
#include <signal.h>
#include <time.h>
#define CLOCKID CLOCK_REALTIME
#define SIG SIGRTMIN
#define errExit(msg) do { perror(msg); exit(EXIT_FAILURE); \
} while (0)
#include <iostream>

using namespace std;

static int flag=0;
class timer{

static void
handler(int sig) {
  printf("Caught signal %d\n", sig);
  ::flag=1;
  signal(sig, handler);
}

public:

void timer_func()
{
timer_t timerid;
struct sigevent sev;
struct itimerspec its;
long long freq_nanosecs=1; // The timer frequency in nanosecs
sigset_t mask;
struct sigaction sa;

/* Establish handler for timer signal */

printf("Establishing handler for signal %d\n", SIG);

sa.sa_flags = SA_RESETHAND;
sa.sa_handler = handler;


 /* Create the timer */

 sev.sigev_notify = SIGEV_SIGNAL;
 sev.sigev_signo = SIG;
 sev.sigev_value.sival_ptr = &timerid;

 if (timer_create(CLOCKID, &sev, &timerid) == -1)
   errExit("timer_create");

 printf("timer ID is 0x%lx\n", (long) timerid);

 /* Start the timer */

 its.it_value.tv_sec = freq_nanosecs / 1000000000;
 its.it_value.tv_nsec = freq_nanosecs % 1000000000;
 its.it_interval.tv_sec = its.it_value.tv_sec;
 its.it_interval.tv_nsec = its.it_value.tv_nsec;

 if (timer_settime(timerid, 0, &its, NULL) == -1)
   errExit("timer_settime");
  }
 };

 int main() {

   timer ob;
   ob.timer_func();

   for(int i=0; i<20; i++) {
     sleep(1);
   if(flag) {
     cout << "Timer called" << endl;
     flag=0;
    }
   cout << "Printing i: " << i << endl;
  }
 } 

但是如果我在其中设置“long long freq_nanosecs = 1”，定时器也只会输出一次。应该重复

Answer 1

0.011 是一个双字面量，您将它分配给一个 long，因此它被转换为 0。这只是将 freq_nanosecs 设置为 0。

long freq_nanosecs=0.011

由于定时器值为 0，这将解除定时器。

timer_settime(timerid, 0, &its, NULL)