select函数（二）

Myth丶恋晨 2022-08-11 07:30 195阅读 0赞

//输入ａ转变为大写Ａ
    #include <stdio.h>
    #include <ctype.h>
    #include <ctype.h>
    #include <unistd.h>
    #include <stdlib.h>
    #include <sys/select.h>
    #define N 1024
    
    int main(void)
    {
    	fd_set rfds, tmp;
    	int retval;
    	int maxfd;
    	struct timeval tv;
    //	char buf[N];
    	char ch, ch_ret;
    	int n;
    
    	FD_ZERO(&rfds);
    	FD_SET(STDIN_FILENO, &rfds);
    	maxfd = STDIN_FILENO;
    
    
    	while(1){
    		tv.tv_sec = 3;
    		tv.tv_usec = 0;
    		tmp = rfds;
    		retval = select(maxfd + 1, &tmp, NULL, NULL, &tv);
    //		retval = select(maxfd + 1, &rfds, NULL, NULL, &tv);
    
    		if(retval == -1){
    			perror("select fail\n");
    			exit(1);
    		}else if(retval > 0){
    			if(FD_ISSET(maxfd, &rfds)){
    				n = read(STDIN_FILENO, &ch, 1);
    
    				if(n == -1){
    					perror("read fail\n");
    					exit(1);
    				}
    				if( ch == 'q' ){
    		//			exit(1);
    					break;
    				}
    				if( ch == '\n'){
    					continue;
    				}
    			 	ch_ret	= toupper(ch);
    				write(STDOUT_FILENO, &ch_ret, 1);
    				putchar('\n');
    				continue;
    			}
    
    		}else if(retval == 0){
    			printf("time out\n");
    			printf("%ld\n", tv.tv_sec);
    //			exit(1);
    		}
    	}
    
    	return 0;
    }
    
    /*
    akaedu@akaedu-G41MT-D3:~/lin/20140820_dop2_select$ ./a.out 
    a
    A
    x
    X
    v
    V
    m
    M
    time out
    0
    time out
    0
    g
    G
    time out
    0
    ^C
    akaedu@akaedu-G41MT-D3:~/lin/20140820_dop2_select$ 
    */
    
    
    
    
    <pre name="code" class="cpp">/* 
     * reads input from pipes p1, p2 
     * using select() for multiplexing 
     *
     * tty1：cat > ./p1
     * tty2：cat > ./p2
     * tty3: ./select
     */  
    #include <fcntl.h>
    #include <stdio.h>
    #include <sys/time.h>
    #include <sys/types.h>
    #include <unistd.h>
    
    int main(void) {
    	int fds[2];  char buf[4096];  
    	int i, rc, maxfd;
    	fd_set watchset;       /* 欲监听read操作的集合 */
    	fd_set inset;          /* select()调用后，被修改的集合 */
    
    	if((fds[0]=open("p1", O_RDONLY|O_NONBLOCK)) < 0){ 
    		perror("open p1"); 
    		return 1; 
    	}
    	if((fds[1]=open("p2", O_RDONLY|O_NONBLOCK)) < 0){ 
    		perror("open p2"); 
    		return 1; 
    	}
    
    	/* 清零集合，将监听描述符加入集合内 */
    	FD_ZERO(&watchset);
    	FD_SET(fds[0], &watchset);
    	FD_SET(fds[1], &watchset);
    
    	/* 找出最大文件描述符， 用以select第一个参数 */
    	maxfd = fds[0] > fds[1] ? fds[0] : fds[1];
    
    	/* 循环监视两个文件描述符是否有read条件*/
    	while(FD_ISSET(fds[0], &watchset) || FD_ISSET(fds[1], &watchset)){
    		inset = watchset;		// backup, 因为select()调用结束会修改参二(传出参数) 
    		if(select(maxfd+1, &inset, NULL,NULL,NULL) < 0){
    			perror("select"); 
    			return 1; 
    		} 
    		//从监听的两个文件描述符中去判断，哪个还在集合中 
    		for(i = 0; i < 2; i++){
    			if(FD_ISSET(fds[i], &inset)){				//具备read条件
    				rc = read(fds[i], buf, sizeof(buf) - 1);//read之
    				if(rc < 0){
    					perror("read"); 
    					return 1;
    				}else if(!rc){
    					/* 管道已经被关闭，无需再监听了 */
    					close(fds[i]);
    					FD_CLR(fds[i], &watchset);			//清除出监听集合中
    				}else{
    					buf[rc] = '\0';
    					printf("read: %s", buf);
    				} 
    			} 
    		} 
    	}
    	return 0;
    }