linux fd 文件描述符

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

int main() {
    int fd;
    char buffer[100];

    // 打开文件
    fd = open("example.txt", O_RDONLY);
    if (fd == -1) {
        perror("open");
        exit(EXIT_FAILURE);
    }

    // 读取文件内容
    ssize_t bytesRead = read(fd, buffer, sizeof(buffer) - 1);
    if (bytesRead == -1) {
        perror("read");
        close(fd);
        exit(EXIT_FAILURE);
    }

    buffer[bytesRead] = '\0'; // 确保字符串以 null 结尾
    printf("Read from file: %s\n", buffer);

    // 关闭文件
    close(fd);

    return 0;
}

# 查看当前文件描述符限制
ulimit -n

# 临时修改文件描述符限制
ulimit -n 2048

#include <fcntl.h>

// 获取文件锁
struct flock fl;
fl.l_type = F_WRLCK;
fl.l_whence = SEEK_SET;
fl.l_start = 0;
fl.l_len = 0;

if (fcntl(fd, F_SETLKW, &fl) == -1) {
    perror("fcntl");
    close(fd);
    exit(EXIT_FAILURE);
}

// 执行文件操作

// 释放文件锁
fl.l_type = F_UNLCK;
if (fcntl(fd, F_SETLK, &fl) == -1) {
    perror("fcntl");
    close(fd);
    exit(EXIT_FAILURE);
}