Question

我试图在C ++中创建一个文件分割器/连接器，但我的分割功能有问题。我使用MP4文件进行快速测试，结果是：其他所有部分都没问题，但最后一部分总是不起作用。我不明白这一点。有人可以向我解释一下吗？这是我的分割功能：

void split_F(const char* file_name, int number_of_part)
{
    FILE *fp_read = fopen(file_name, "rb");

    //calculate file size
    int file_size;
    fseek(fp_read, 0L, SEEK_END);
    file_size = ftell(fp_read);
    rewind(fp_read); //reset file pointer

    //calculate number of parts
    //int number_of_part = (int)ceil((double)file_size / size_of_part);
    long size_of_part;
    size_of_part = (int)floor((double)file_size / number_of_part);
    cout << "Total files after split: " << number_of_part << endl
        << "...Processing..." << endl;

    //main process
    char name[255] = "";
    for (int count = 1; count <= number_of_part; count++) 
    {
        sprintf(name, "%s.part_%03d", file_name, count);
        FILE *fp_write = fopen(name, "wb");

        //create buffer
        char *buffer = new char[size_of_part];
        memset(buffer, NULL, size_of_part); //reset buffer

        fread(buffer, size_of_part, 1, fp_read);
        fwrite(buffer, size_of_part, 1, fp_write);
        fseek(fp_read, count*size_of_part, SEEK_SET);

        cout << "> File: " << name << " done babe!" << endl;

        delete[] buffer;
        fclose(fp_write);
    }
        fclose(fp_read);
}

Answer 1

最后一部分可能比size_of_part更小或更大，因为原始文件大小不是它的倍数。

您需要自动调整最后一部分的大小。

例如，如果文件大小为1000字节，则为7个部分。您的计算文件大小为142. 7 * 142 = 994，您缺少最后6个字节。这是你的问题吗？

不需要fseek，你为什么要使用它？您只需要按顺序读取输入文件

void split_F(const char* file_name, int number_of_part)
{
    FILE *fp_read = fopen(file_name, "rb");

    //calculate file size
    int file_size;
    fseek(fp_read, 0L, SEEK_END);
    file_size = ftell(fp_read);
    rewind(fp_read); //reset file pointer

    //calculate number of parts
    long size_of_part;
    size_of_part = (int)ceil((double)file_size / number_of_part);
    cout << "Total files after split: " << number_of_part << endl
        << "...Processing..." << endl;

    //main process
    char name[255] = "";
    int bytesRemaining = file_size;

    //create buffer, we reuse it for each part
    char *buffer = new char[size_of_part];

    //No need to reset buffer
    //memset(buffer, NULL, partSize);


    for (int count = 1; count <= number_of_part; count++) 
    {
        sprintf(name, "%s.part_%03d", file_name, count);
        FILE *fp_write = fopen(name, "wb");

        int partSize;
        if(bytesRemaining > size_of_part)
        {
            partSize = size_of_part;
        }
        else
        {
            partSize = bytesRemaining;
        }

        fread(buffer, partSize, 1, fp_read);
        fwrite(buffer, partSize, 1, fp_write);

        cout << "> File: " << name << " done babe!" << endl;

        fclose(fp_write);
    }
    fclose(fp_read);
    delete[] buffer;
}

Answer 2

您正在计算size_of_part作为文件大小和请求的部件数的舍入商。然后，您继续以该确切大小的块读取文件。除非文件大小是number_of_parts的倍数，否则这将失败。您需要修复代码以允许最后一部分小于size_of_part。

Answer 3

您的文件可能不会分成相等长度的N个部分（假设文件长度为7个字节，您将其分为3个部分......？）

long remaining_size = file_size;
long size_of_part;
size_of_part = (file_size + number_of_part - 1) / number_of_part;

这使得零件长度向上舍入，因此最后一个零件可能比前面的所有零件短。

//create buffer
char *buffer = new char[size_of_part];

//main process
char name[255] = "";
for (int count = 1; count <= number_of_part; count++) 
{
    sprintf(name, "%s.part_%03d", file_name, count);
    FILE *fp_write = fopen(name, "wb");

    long this_part_size =
        remaining_size < size_of_part ? remaining_size : size_of_part;

    fread(buffer, this_part_size, 1, fp_read);
    fwrite(buffer, this_part_size, 1, fp_write);

    cout << "> File: " << name << " done babe!" << endl;

    fclose(fp_write);

    remaining_size -= this_part_size;
}
delete[] buffer;

C ++中的文件分割器

3 个答案: