Linux 函数学习

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;}