C++ sleep()和usleep()的区别

sleep() 和 usleep()主要区别前者单位为秒，后者为微妙（*1e6）

C++ sleep() 和 usleep()

代码如下：设置一个时间参数，分别向sleep()和usleep()方法传入该参数，打印sleep和usleep前后的系统时间戳

#include <time.h>
#include <stdio.h>
#include <IOStream>
#include <unistd.h>

using namespace std;
int main(int argc, char *argv[]){
  int sleep_time = 100;
  cout << "sleep before time: " << time(NULL) << endl;
  sleep(sleep_time);
  cout << "sleep after time: " << time(NULL) << endl;

  cout << "======================" << endl;

  cout << "usleep before time: " << time(NULL) << endl;
  usleep(sleep_time);
  cout << "usleep after time: " << time(NULL) << endl;
}

运行结果：

sleep before time: 1560257692

sleep after time: 1560257792

======================

usleep before time: 1560257792

usleep after time: 1560257792js

从运行结果来看，sleep()方法执行前后的时间戳相减正好是sleep_time大小，打印的时间戳是以秒为单位的，所以sleep()方法将程序挂起使用的单位是秒级别的；从usleep()执行前后的时间戳来看，感觉上程序并没有被挂起，这是编程因为usleep()方法将程序挂起的使用的单位是微秒级别的（1,000,000 微秒 = 1秒）所以程序看起来并没有被挂起，下面我们将打印的时间戳改为微秒级别的看看。

可以通过<sys/time.h>库中的gettimeofday()方法来拿到当前系统的微秒级别时间。

#include <stdio.h>
#include <iostream>
#include <unistd.h>
#include <sys/time.h>

using namespace std;
int main(int argc, char *argv[]){
  int sleep_time = 100;
  cout << "sleep before time: " << time(NULL) << endl;
  sleep(sleep_time);
  cout << "sleep after time: " << time(NULL) << endl;

  cout << "======================" << endl;

  cout << "usleep before time: " << time(NULL) << endl;
  usleep(sleep_time);
  cout << "usleep after time: " << time(NULL) << endl;

  cout << "======================" << endl;
  struct timeval tv; 
  gettimeofday(&tv,NULL);编程客栈
  cout << "not usleep before time: " << tv.tv_sec<<"s,"<<tv.tv_usec<<"微秒"<<endl;
  usleep(0);
  gettimeofday(&tv,NULL);
  cout << 编程"not usleep after time: " << tv.tv_sec<<"s,"<<tv.tv_usec<<"微秒"<<endl;
  cout << "======================" << endl;
  gettimeofday(&tv,NULL);
  cout << "usleep before time: " << tv.tv_sec<<"s,"<<tv.tv_usec<<"微秒"<<endl;
  usleep(sleep_time);
  gettimeofday(&tv,NULL);
  cou编程客栈t << "usleep after time: " << tv.tv_sec<<"s,"<<tv.tv_usec<<"微秒"<<endl;
}

运行结果

sleep before time: 1560260201

sleep after time: 1560260301

======================

usleep before time: 1560260301

usleep after time: 156026开发者_Js入门0301

======================

not usleep before time: 1560260301s,491772微秒

not usleep after time: 1560260301s,491948微秒

======================

usleep before time: 1560260301s,491962微秒

usleep after time: 1560260301s,492191微秒

从使用usleep(0)和使用了usleep(100)方法来看，执行前后的时间差差不多相差100，从而可以看出usleep()是以微秒级别为单位的。

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