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 + 1while(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;}