第五講 進階檔案操作#include <fcntl.h>#include <stdio.h>#include <unistd.h> int main(){ int fds[2]; char buf[4096]; int i, fd; if ((fds[0] = open("p1",O_RDONLY)) < 0) { perror("open"); return 1; } if (fds[1] = open("p2",O_RDONLY) < 0) { perror("open p2"); return 1; } fd = 0; while (1) { i = read(fds[fd],buf,sizeof(buf) - 1); if (i < 0) { perror("read"); return 1; } else if (!i) { printf("pipe close/n"); return 0; } buf[i] = '/0'; printf("read:%s", buf); fd = (fd + 1) % 2; } return 0;}[root@localhost tmp]mknod p1 p[root@localhost tmp]mknod p2 p[root@localhost tmp]gcc –o mpxb1 mpxb1.c[root@localhost tmp]./mpxb1 // 在終端一中運行[root@localhost tmp]cat > p1 // 在終端二中運行test1[root@localhost tmp]cat > p2 // 在終端三中運行test2[root@localhost tmp]./mpxb1 // 在終端一中運行read:test1對於test2不能顯示啊多路輸入輸出#include <sys/poll.h>int poll(struct pollfd *fds, int numfds, int timeout);struct pollfd{ int fd; short events; short revents;}POLLIN, POLLPRI, POLLOUT, POLLERR, POLLHUP, POLLNVAL例#include <fcntl.h>#include <stdio.h>#include <sys/poll.h>#include <unistd.h> int main(){ struct pollfd fds[2]; char buf[4096]; int i, rc; if ((fds[0].fd = open("p1", O_RDONLY|O_NONBLOCK)) < 0) { perror("open p1"); return 1;: } if ((fds[1].fd = open("p2", O_RDONLY | O_NONBLOCK)) < 0) { perror("open p2"); return 0; } fds[0].events = POLLIN; fds[1].events = POLLIN; while (fds[0].events || fds[1].events) { if (poll(fds, 2, 0)) { perror("poll"); return 1; } for (i = 0; i < 2; i++) { if (fds[i].revents) { rc = read(fds[i].fd, buf, sizeof(buf) - 1); if ( rc < 0 ) { perror("read"); return 1; } else if (!rc) { fds[i].events = 0; } else { buf[rc] = '/n'; printf("read:%s", buf); } } } } return 0;} #include <sys/select.h>int select(int numfds, fd_set *readfds, fd_set *writefds, fd_set *exceptfds, struct timeval *timeout);FD_ZERO(fd_set *fds); FD_SET(int fd, fd_set *fds);FD_CLR(int fd, fd_set *fds); FD_ISSET(int fd, fd_set *fds);#include <sys/time.h>struct timeval{ int tv_sec; int tv_usec;}例#include <fcntl.h>#include <stdio.h>#include <sys/select.h>#include <unistd.h> int main(void){ int fds[2]; char buf[4096]; int i, rc, maxfd; fd_set watchset; fd_set inset; if (fds[0] = open("p1", O_RDONLY | O_NONBLOCK) < 0) { perror("open p1"); return 1; } if (fds[1] = open("p2", O_RDONLY | O_NONBLOCK) < 0) { perror("open p2"); return 1; } FD_ZERO(&watchset); FD_SET(fds[0], &watchset); FD_SET(fds[1], &watchset); maxfd = fds[0] > fds[1] ? fds[0] : fds[1]; while (FD_ISSET(fds[0], &watchset) || FD_ISSET(fds[1], &watchset)) { inset = watchset; if (select( maxfd + 1, &inset, NULL, NULL, NULL) < 0) { perror("select"); return 1; } for ( i = 0; i < 2; i++) { if(FD_ISSET(fds[i], &inset)) { rc = read(fds[i], buf, sizeof(buf) - 1); if (rc < 0) { perror("read"); return 1; } else if (!rc) { close(fds[i]); FD_CLR(fds[i], &watchset); } else { buf[rc] = '/0'; printf("read:%s", buf); } } } } return 0;}比較poll()和select()例#include <fcntl.h>#include <stdio.h>#include <stdlib.h>#include <sys/select.h>#include <sys/poll.h>#include <unistd.h>#include <signal.h> int gotAlarm; void catch(int sig){ gotAlarm = 1;} #define HIGH_FD 1000 int main( int argc ,const char *argv){ int devZero; int count; fd_set selectFds; struct pollfd pollfds; devZero = open("dev/zero",O_RDONLY); dup2(devZero, HIGH_FD); signal(SIGALRM, catch); gotAlarm = 0; count = 0; alarm(1); while (!gotAlarm) { FD_ZERO(&selectFds); FD_SET(HIGH_FD, &selectFds); select(HIGH_FD + 1, &selectFds, NULL, NULL, NULL); count++; } printf("select() calls per second :%d/n", count); pollfds.fd = HIGH_FD; pollfds.events = POLLIN; count = 0; gotAlarm = 0; alarm(1); while (!gotAlarm) { poll(&pollfds, 0, 0); count++; } printf("poll() calls per second :%d/n", count); return 0;} #include <sys/epoll.h>int epoll_create(int numDescriptors);int epoll_ctl(int epfd, int op, int fd, struct epoll_event *event);int epoll_wait(int epfd, struct epoll_event *events, int maxevents, int timeout);struct epoll_event{ union{ void *ptr; int fd; unsigned int u32; unsigned long long u64;} data;}EPOLLIN, EPOLLOUT, EPOLLPRIEPOLL_CTL_ADD, EPOLL_CTL_DEL, EPOLL_CTL_MODread和write的替代例#include <sys/uio.h>struct iovec{void *iov_base;void *iov_len;};int readv(int fd, const struct iovec *vector, sieze_t count);int writev(int fd, const struct iovec *vector, size_t count);例#include <unistd.h>#include <stdio.h>#include <sys/uio.h> int main(){ struct iovec buffers[3]; buffers[0].iov_base = "hello"; buffers[0].iov_len = 5; buffers[1].iov_base = " "; buffers[1].iov_len = 1; buffers[2].iov_base = "world/n"; buffers[2].iov_len = 6; writev(1,buffers, 3); return 0;}
