在C中将文本追加到文件开头不起作用

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

void prepend_to_file(const char *filename, const char *text) {
    FILE *file = fopen(filename, "r");
    if (file == NULL) {
        perror("Error opening file");
        return;
    }

    // 获取文件大小
    fseek(file, 0, SEEK_END);
    long file_size = ftell(file);
    fseek(file, 0, SEEK_SET);

    // 分配缓冲区
    char *buffer = (char *)malloc(file_size + 1);
    if (buffer == NULL) {
        perror("Error allocating memory");
        fclose(file);
        return;
    }

    // 读取文件内容到缓冲区
    fread(buffer, 1, file_size, file);
    buffer[file_size] = '\0';

    // 关闭文件
    fclose(file);

    // 打开文件以写入
    file = fopen(filename, "w");
    if (file == NULL) {
        perror("Error opening file for writing");
        free(buffer);
        return;
    }

    // 在缓冲区开头添加新文本
    char *new_buffer = (char *)malloc(strlen(text) + file_size + 1);
    if (new_buffer == NULL) {
        perror("Error allocating memory");
        fclose(file);
        free(buffer);
        return;
    }
    strcpy(new_buffer, text);
    strcat(new_buffer, buffer);

    // 写入新内容到文件
    fwrite(new_buffer, 1, strlen(new_buffer), file);

    // 关闭文件并释放内存
    fclose(file);
    free(buffer);
    free(new_buffer);
}

int main() {
    const char *filename = "example.txt";
    const char *text = "New content at the beginning.\n";
    prepend_to_file(filename, text);
    return 0;
}