selsect 函数（一）

古城微笑少年丶 2022-08-11 07:30 21阅读 0赞

/*
     *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$ 
    */