select.c

linuxI/O的基础编程实例

/*select.c*/
#include <fcntl.h>
#include <stdio.h>
#include <unistd.h>
#include <stdlib.h>
#include <time.h>

int main(void)
{
	int fds[2];
	char buf[7];
	int i,rc,maxfd;
	fd_set inset1,inset2;
	struct timeval tv;
/*首先按一定的权限打开hello1文件*/
	if((fds[0]=open("hello1",O_RDWR | O_CREAT, 0666))<0)
		perror("open hello1");
/*在按一定的权限打开hello2*/
	if((fds[1]=open("hello2", O_RDWR | O_CREAT,0666))<0)
		perror("open hello2");

	if((rc=write(fds[0],"hello!\n",7)))
		printf("rc=%d\n",rc);
	lseek(fds[0],0,SEEK_SET);
/*取出两个文件描述符中的较大者*/	

	maxfd=fds[0]>fds[1] ? fds[0]: fds[1];
/*初始化读集合inset1，并加入相应的描述符*/

	FD_ZERO(&inset1);
	FD_SET(fds[0],&inset1);
/*初始化写集合inset2，并加入相应的描述符*/	

	FD_ZERO(&inset2);
	FD_SET(fds[1],&inset2);
	tv.tv_sec=2;
	tv.tv_usec=0;
/*循环测试该文件描述符是否准备就绪，并调用select函数对相关文件描述符做对应操作*/
	while(FD_ISSET(fds[0],&inset1) || FD_ISSET(fds[1],&inset2))
	{
		if(select(maxfd+1,&inset1,&inset2,NULL,&tv)<0)
			perror("select");
		else
		{
			if(FD_ISSET(fds[0], &inset1))
			{
				rc=read(fds[0],buf,7);
				if(rc>0)
				{
					buf[rc]='\0';
					printf("read:%s\n",buf);
				}
				else
				{
					perror("read error");
				}
			}
			if(FD_ISSET(fds[1],&inset2))
			{
				rc=write(fds[1],buf,7);
				if(rc>0)
				{
					buf[rc]='\0';
					printf("rc=%d,write:%s\n",rc,buf);
				}
				else
				{
					perror("write error");
				}
			sleep(10);
			}
		}
	}
	exit(0);
}