What's wrong with the maximum filename length limit?

Question

Qt

In general, I found that under Windows the limit is 255 characters, and under Linux it is 255 bytes, and I wrote this code to copy files with renaming (there, the coordinates of rectangles are stored in the name, and there can be a lot of them, not the best solution, but this is not I figured it out).

std::string filename = current_image->path().stem().string();

        #if OS == LINUX
        for (const auto& ch : filename)
            if (!std::isalpha(ch) && !std::isdigit(ch) &&
                ch != ' ' && ch != '.' &&ch != '-' && ch != '_')
            {
                QMessageBox::warning(
                    this, "Warning",
                    "Файл не будет сохранён, т.к. содержит недопустимые символы в "
                    "своём имени.\nДопустимые символы: латинские буквы, цифры, "
                    "пробел, точка, '-' и '_'."
                );

                goto filename_invalidity;
            }
        #endif

        for (const auto& rect : rect_grabber->getRects())
        {
            std::string rect_data = "_["
                + std::to_string(rect.x()) + "," + std::to_string(rect.y()) + ","
                + std::to_string(rect.width()) + "," + std::to_string(rect.height()) + ","
                + rect.getType() + "]";

            if (filename.size() + rect_data.size()
                    + current_image->path().extension().string().size() <= 255)
            {
                filename += rect_data;
            }
            else
            {
                QMessageBox::warning(
                    this, "Warning",
                    "Имя файла превысило максимально допустимую длину (255 символов)."
                    " Часть данных разметки не будет сохранена в имени файла."
                );

                break;
            }
        }

        filename += current_image->path().extension().string();

        fs::copy(current_image->path(),fs::path{load_window->getOutDirPath()/filename});
    }

All this crashes immediately after the second QMessageBox::warning is displayed, i.e. when saving with renaming. But the algorithm itself excludes the situation that more than 255 characters will be stored (including the dot extension). What's wrong?

Answer 1

Under Windows, the limit is 32 kilobytes. Look for the corresponding functions, by the way, this is also in Linux. Plus there is a damn joke to create a folder, go into it and create a folder. In general, all descriptors on the file system are selected, and you can delete it only by going down and deleting folders by going up

Answer 2

In general, I found that under Windows the limit is 255 characters

Not in "windows", but specifically in the explorer. NTFS works great with much longer paths too - it doesn't care. But the conductor does not know how. Tellingly, some of the Windows application APIs ignore this restriction, causing the application to save the file with a longer path. Then it gets uncomfortable.

Answer 3

Correction - this glitch is 255 characters - not only the name, but the whole path to it. But again - there is no restriction - this is the jamb of the default explorer and nothing more.