Linux函数学习 select

1、Linux select 函数

int select(int nfds, fd_set *readfds, fd_set *writefds,
fd_set *exceptfds, struct timeval *timeout);

nfds 最大文件fd + 1

readfds 监听可读文件集合fd

writefds 监听可写文件集合fd

exceptfd 监听异常文件集合fd

timeout 超时时间

2、函数实例

#include <stdio.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <errno.h>
#include <linux/input.h>
#include <unistd.h>
#include <sys/select.h>
#include <string.h>

static char * eventTypeToString(__u16 type){
	switch(type){
		case EV_SYN:
			return "EV_SYN";
		case EV_KEY:
			return "EV_KEY";
		case EV_REL:
			return "EV_REL";
		case EV_ABS:
			return "EV_ABS";
		case EV_MSC:
			return "EV_MSC";
		case EV_SW:
			return "EV_SW";
		default:
			return "UNKOWN";
	}
}

static char * eventCodeToString(__u16 code){
	switch(code){
		case KEY_ESC:
			return "KEY_ESC";
		case KEY_POWER:
			return "KEY_POWER";
		default:
			return "UNKOWN";
	}
}


int main (int argc, char ** argv){

	int fd; 
	/*需要轮询的fds*/
	fd_set readfds;
	/*需要轮询的fds数量*/
	int maxfds;
	struct input_event event;
	struct timeval timeout;
	timeout.tv_sec = 10;
	timeout.tv_usec = 0;

	if(argc != 2){
		printf("Usage: %s <dev> \n", argv[0]);
	}
	
	fd = open(argv[1], O_RDWR | O_NONBLOCK);
	if(fd < 0){
		printf("open %s err = %s\n", argv[1],strerror(errno));
		return 0;
	} else {
		printf("open %s success \n",argv[1]);
	}
	
	//清零
	FD_ZERO(&readfds);
	
	/*将标准输入的文件描述符添加到集合中, 如果是多个添加多个文件描述符*/
	FD_SET(fd, &readfds);
	
	maxfds = fd + 1; //最大文件描述符fd + 1
	while(1){
		int ret = select(maxfds, &readfds, NULL, NULL, NULL);
		if(ret > 0){
			/*只有发生过的fd才会在文件readfds中*/
			if(FD_ISSET(fd, &readfds)){
				while(read(fd, &event, sizeof(event)) == sizeof(event)){
					printf("get envent: type = 0x%x, Code = 0x%x value = 0x%x \n",event.type, event.code, event.value);
					printf("get envent: type = %s, Code = %s value = 0x%x \n",eventTypeToString(event.type), eventCodeToString(event.code), event.value);
				}
			}
			//将文件描述符重置
			FD_ZERO(&readfds);
		    FD_SET(fd, &readfds); 
		} else if (ret == 0){
			if(FD_ISSET(fd, &readfds)){
				printf("select time out \n");
			}
		} else {
			perror("poll err \n");
		}
	}

	return 0;

}