非阻塞轮询读终端和等待超时

1、非阻塞轮询读终端

#include <unistd.h>#include <fcntl.h>#include <errno.h>#include <string.h>#include <stdlib.h>#define MSG_TRY "try again\n"int main(void){char buf[10];int fd, n;fd = open("/dev/tty", O_RDONLY|O_NONBLOCK);if(fd<0) {perror("open /dev/tty");exit(1);}tryagain:n = read(fd, buf, 10);if (n < 0) {if (errno == EAGAIN) {sleep(1);write(STDOUT_FILENO, MSG_TRY, strlen(MSG_TRY));goto tryagain;}perror("read /dev/tty");exit(1);}write(STDOUT_FILENO, buf, n);close(fd);return 0;}

2、非阻塞轮询读终端和等待超时#include <unistd.h>#include <fcntl.h>#include <errno.h>#include <string.h>#include <stdlib.h>#define MSG_TRY "try again\n"#define MSG_TIMEOUT "timeout\n"int main(void){char buf[10];int fd, n, i;fd = open("/dev/tty", O_RDONLY|O_NONBLOCK);if(fd<0) {perror("open /dev/tty");exit(1);}for(i=0; i<5; i++) {n = read(fd, buf, 10);if(n>=0)break;if(errno!=EAGAIN) {perror("read /dev/tty");exit(1);}sleep(1);write(STDOUT_FILENO, MSG_TRY, strlen(MSG_TRY));}if(i==5)write(STDOUT_FILENO, MSG_TIMEOUT, strlen(MSG_TIMEOUT));elsewrite(STDOUT_FILENO, buf, n);close(fd);return 0;}