selsect 函数（一）

/*
 *用户使用键盘循环输入字符，select监听终端，将用户输入的字符输出到终端上
 *如果用户指定时间内没有做输入，提示超时，用户输入‘q’退出。
 */
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <fcntl.h>
#include <sys/select.h>

int main(void)
{
	fd_set rfds, inset;
	struct timeval tv;
	int retval, n, max_fd;
	char ch;

	max_fd = open("/dev/tty", O_RDONLY);
	if(max_fd < 0){
		perror("open /dev/tty error");
		exit(1);
	}

	FD_ZERO(&rfds);
	FD_SET(max_fd, &rfds);

	while(1){
		tv.tv_sec = 3;		//每个字符都设置一次超时上限
		tv.tv_usec = 600;	//所以这个应该至于循环中

		inset = rfds;		//***保证监听的文件描述符始终在集合中
		retval = select(max_fd+1, &inset, NULL, NULL, &tv);
		if(retval == -1){
			perror("select error");
			exit(1);
		}else if(retval){	//retval>0说明监听的集合中有改变
			if(FD_ISSET(max_fd, &inset)){//所关心的文件应在集合中
				n = read(max_fd, &ch, 1);
				if(n < 0){ 
					perror("read error"); 
					exit(1); 
				}
				if('q' == ch){ 
					break; 
				}
				if('\n' == ch){			//用户直接回车，忽略其操作
					continue;
				}
				write(1, &ch, n);
				putchar('\n');
				//printf("tv.tv_sec = %ld\n", tv.tv_sec);
				//printf("tv.tv_usec = %ld\n", tv.tv_usec);
				continue;
			}
		}else{				//retval == 0
			printf("time out!\n");
				printf("tv.tv_sec = %ld\n", tv.tv_sec);
				printf("tv.tv_usec = %ld\n", tv.tv_usec);
		}
	}

	return 0;
}

/*akaedu@akaedu-G41MT-D3:~/桌面/T74_system/0820_chp1_dup2_select$ ./select2
a
a
x
x
time out!
tv.tv_sec = 0
tv.tv_usec = 0
time out!
tv.tv_sec = 0
tv.tv_usec = 0
d
d
time out!
tv.tv_sec = 0
tv.tv_usec = 0
^C
akaedu@akaedu-G41MT-D3:~/桌面/T74_system/0820_chp1_dup2_select$ 
*/


<pre name="code" class="cpp">#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <sys/select.h>

#define N 1024
#define FOUND "found data! It's:"

int main(void)
{
	fd_set rfds;
	struct timeval tv;
	int retval, n;
	int max_fd;			//所关心的最大文件描述符

	char buf[N];

	FD_ZERO(&rfds);		//将可读文件描述符集合清零
	FD_SET(STDIN_FILENO, &rfds);	//将(fd 0)添加到集合中
	max_fd = STDIN_FILENO;			//只关心标准输入

	tv.tv_sec = 5;		//等待超时上限设置为5秒
	tv.tv_usec = 0;
						//只关心可读集合
	retval = select(max_fd+1, &rfds, NULL, NULL, &tv);

	if(retval == -1){	//返回-1说明出错，errno会被设置
		perror("select error");		
		exit(1);
	}else if(retval > 0){//监听集合中，改变个数大于0
		if(FD_ISSET(STDIN_FILENO, &rfds)){	//所关心的仍应在集合中
			n = read(STDIN_FILENO, buf, N);
			if(n == -1){
				perror("read error");
				exit(1);
			}
			write(STDOUT_FILENO, FOUND, strlen(FOUND));
			write(STDOUT_FILENO, buf, n);
		}
	}else				//在指定时间范围内没有数据到达
		printf("time out... no data arrive\n");
	
	return 0;
}

/*akaedu@akaedu-G41MT-D3:~/桌面/T74_system/0820_chp1_dup2_select$ ./select1
a
found data! It's:a
akaedu@akaedu-G41MT-D3:~/桌面/T74_system/0820_chp1_dup2_select$ ./select1
time out... no data arrive
akaedu@akaedu-G41MT-D3:~/桌面/T74_system/0820_chp1_dup2_select$ 
*/