使用fcntl系统函数在Linux下改变文件属性的操作指南

#include <fcntl.h>

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

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

int main() {
    int fd = open("example.txt", O_RDWR | O_CREAT, 0644);
    if (fd == -1) {
        perror("open");
        exit(EXIT_FAILURE);
    }

    // 获取当前的文件描述符标志
    int flags = fcntl(fd, F_GETFL);
    if (flags == -1) {
        perror("fcntl F_GETFL");
        exit(EXIT_FAILURE);
    }

    // 设置非阻塞模式
    flags |= O_NONBLOCK;
    if (fcntl(fd, F_SETFL, flags) == -1) {
        perror("fcntl F_SETFL");
        exit(EXIT_FAILURE);
    }

    printf("File descriptor %d is now in non-blocking mode.\n", fd);
    close(fd);
    return 0;
}

#include <fcntl.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/stat.h>

int main() {
    int fd = open("example.txt", O_RDWR | O_CREAT, 0644);
    if (fd == -1) {
        perror("open");
        exit(EXIT_FAILURE);
    }

    struct flock lock;
    lock.l_type = F_WRLCK;  // 写锁
    lock.l_whence = SEEK_SET;
    lock.l_start = 0;
    lock.l_len = 0;  // 锁定整个文件

    // 尝试获取锁
    if (fcntl(fd, F_SETLK, &lock) == -1) {
        perror("fcntl F_SETLK");
        exit(EXIT_FAILURE);
    }

    printf("File descriptor %d has acquired a write lock.\n", fd);

    // 释放锁
    lock.l_type = F_UNLCK;
    if (fcntl(fd, F_SETLK, &lock) == -1) {
        perror("fcntl F_SETLK");
        exit(EXIT_FAILURE);
    }

    close(fd);
    return 0;
}

#include <fcntl.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <errno.h>

int main() {
    int fd = open("example.txt", O_RDWR | O_CREAT, 0644);
    if (fd == -1) {
        perror("open");
        exit(EXIT_FAILURE);
    }

    struct flock lock;
    lock.l_type = F_WRLCK;
    lock.l_whence = SEEK_SET;
    lock.l_start = 0;
    lock.l_len = 0;

    // 尝试获取锁
    if (fcntl(fd, F_SETLK, &lock) == -1) {
        if (errno == EACCES || errno == EAGAIN) {
            printf("File is already locked by another process.\n");
        } else {
            perror("fcntl F_SETLK");
        }
        exit(EXIT_FAILURE);
    }

    printf("File descriptor %d has acquired a write lock.\n", fd);

    // 保持锁一段时间
    sleep(5);

    // 释放锁
    lock.l_type = F_UNLCK;
    if (fcntl(fd, F_SETLK, &lock) == -1) {
        perror("fcntl F_SETLK");
        exit(EXIT_FAILURE);
    }

    close(fd);
    return 0;
}