Linux 函数学习 poll

1、Linux poll 函数

int poll(struct pollfd *fds, nfds_t nfds, int timeout);

fds： 需要轮询的fd集合

nfds：需要轮询的fds数量

timeout：超时时间

返回值：0 超时，<0 发生异常，> 0 存在数据变化

2、函数用例

#include <poll.h>
#include <stdio.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <errno.h>
#include <linux/input.h>
#include <unistd.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; 
	int err;
	int len;
	/*需要轮询的fds*/
	struct pollfd fds[1];
	/*需要轮询的fds数量*/
	nfds_t nfds = 1;
	struct input_event event;

	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 \n", argv[1]);
	} else {
		printf("open %s success \n",argv[1]);
	}

	while(1){
		fds[0].fd = fd;
		fds[0].events = POLLIN;
		fds[0].revents = 0;
		int ret = poll(fds,nfds,5000);
		printf("ret = %d \n", ret);
		if(ret > 0){
			if(fds[0].revents == POLLIN){
				while(read(fd, &event, sizeof(event)) == sizeof(event)){
					printf("get envent: type =0x%x, Code = 0x%x value = 0x%x",event.type, event.code, event.value);
				}
			}
		} else if (ret == 0){
			printf("time out \n");
		} else {
			perror("poll err \n");
		}
	}

	return 0;

}

3、代码运行效果

编译二进制文件，运行到手机端