linux+设置read阻塞

#include <fcntl.h>
#include <unistd.h>

int fcntl(int fd, int cmd, ... /* arg */ );

#include <fcntl.h>
#include <unistd.h>
#include <stdio.h>

int main() {
    int fd = open("example.txt", O_RDONLY);
    if (fd == -1) {
        perror("open");
        return 1;
    }

    // 获取当前的文件状态标志
    int flags = fcntl(fd, F_GETFL, 0);
    if (flags == -1) {
        perror("fcntl F_GETFL");
        close(fd);
        return 1;
    }

    // 清除O_NONBLOCK标志，设置为阻塞模式
    flags &= ~O_NONBLOCK;
    if (fcntl(fd, F_SETFL, flags) == -1) {
        perror("fcntl F_SETFL");
        close(fd);
        return 1;
    }

    // 现在fd处于阻塞模式，read操作会等待直到有数据可读
    char buffer[100];
    ssize_t bytesRead = read(fd, buffer, sizeof(buffer));
    if (bytesRead == -1) {
        perror("read");
    } else {
        printf("Read %ld bytes: %.*s\n", bytesRead, (int)bytesRead, buffer);
    }

    close(fd);
    return 0;
}

#include <sys/select.h>

fd_set readfds;
struct timeval timeout;

FD_ZERO(&readfds);
FD_SET(fd, &readfds);

timeout.tv_sec = 5; // 设置超时时间为5秒
timeout.tv_usec = 0;

int ret = select(fd + 1, &readfds, NULL, NULL, &timeout);
if (ret == -1) {
    perror("select");
} else if (ret == 0) {
    printf("select timeout\n");
} else {
    if (FD_ISSET(fd, &readfds)) {
        // 数据可读，执行read操作
    }
}