怎么进去linux读写模式

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

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

    // 打开文件以进行读写操作
    fd = open("example.txt", O_RDWR | O_CREAT, 0666);
    if (fd == -1) {
        perror("open");
        exit(EXIT_FAILURE);
    }

    // 写入数据到文件
    const char *data = "Hello, World!";
    write(fd, data, strlen(data));

    // 将文件指针移回文件开头
    lseek(fd, 0, SEEK_SET);

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

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

int main() {
    FILE *file;
    char buffer[100];

    // 打开文件以进行读写操作
    file = fopen("example.txt", "r+");
    if (file == NULL) {
        perror("fopen");
        exit(EXIT_FAILURE);
    }

    // 写入数据到文件
    const char *data = "Hello, World!";
    fwrite(data, sizeof(char), strlen(data), file);

    // 将文件指针移回文件开头
    fseek(file, 0, SEEK_SET);

    // 读取文件内容
    size_t bytesRead = fread(buffer, sizeof(char), sizeof(buffer) - 1, file);
    if (bytesRead == 0 && ferror(file)) {
        perror("fread");
        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
    fclose(file);

    return 0;
}

fd = open("example.txt", O_RDWR | O_CREAT, 0666);

lseek(fd, 0, SEEK_SET); // 将文件指针移回文件开头