如何在read()函数调用中实现超时? [英] How to implement a timeout in read() function call?

问题描述

我想使用串行com端口进行通信，并且每次调用 read()函数调用时都想实现超时.

I want to use serial com port for communication and I want to implement a timeout every time I call the read() function call.

int filedesc = open( "dev/ttyS0", O_RDWR );

read( filedesc, buff, len );

我正在使用Linux OS.如何使用选择函数调用来实现?

I'm using Linux OS. How to implement using select function call?

推荐答案

select()需要5个参数，首先是最高的文件描述符+ 1，然后是fd_set用于读取，一个用于写入，一个用于异常.最后一个参数是struct timeval，用于超时.错误时返回-1，超时时返回0或设置的集合中文件描述符的数量.

select() takes 5 parameters, first the highest file descriptor + 1, then a fd_set for read, one for write and one for exceptions. The last parameter is a struct timeval, used for timeout. It return -1 on error, 0 on timeout or the number of file descriptors in the sets that are set.

#include <stdio.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <sys/select.h>

int main(void)
{
  fd_set set;
  struct timeval timeout;
  int rv;
  char buff[100];
  int len = 100;
  int filedesc = open( "dev/ttyS0", O_RDWR );

  FD_ZERO(&set); /* clear the set */
  FD_SET(filedesc, &set); /* add our file descriptor to the set */

  timeout.tv_sec = 0;
  timeout.tv_usec = 10000;

  rv = select(filedesc + 1, &set, NULL, NULL, &timeout);
  if(rv == -1)
    perror("select"); /* an error accured */
  else if(rv == 0)
    printf("timeout"); /* a timeout occured */
  else
    read( filedesc, buff, len ); /* there was data to read */
  close(filedesc);
}

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