如何在内存映射文件中写入长字符串？

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

int main() {
    const char* file_path = "example.txt";
    const char* long_string = "This is a long string that we want to write into the memory-mapped file.";

    // 打开或创建内存映射文件
    int fd = open(file_path, O_RDWR | O_CREAT | O_TRUNC, S_IRUSR | S_IWUSR);
    if (fd == -1) {
        perror("open");
        exit(1);
    }

    // 设置内存映射文件的大小
    off_t file_size = strlen(long_string);
    if (ftruncate(fd, file_size) == -1) {
        perror("ftruncate");
        exit(1);
    }

    // 映射内存映射文件到内存
    char* mapped_data = mmap(NULL, file_size, PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0);
    if (mapped_data == MAP_FAILED) {
        perror("mmap");
        exit(1);
    }

    // 将长字符串复制到内存映射文件
    strcpy(mapped_data, long_string);

    // 刷新内存映射文件到磁盘
    if (msync(mapped_data, file_size, MS_SYNC) == -1) {
        perror("msync");
        exit(1);
    }

    // 解除内存映射
    if (munmap(mapped_data, file_size) == -1) {
        perror("munmap");
        exit(1);
    }

    // 关闭文件
    if (close(fd) == -1) {
        perror("close");
        exit(1);
    }

    printf("Long string has been written to the memory-mapped file.\n");

    return 0;
}