What's the optimal way to read QFile into a `vector<char> buffer`?

shenlebantongying

We have an app that read a large chunk of data frequently from various files via QFile::readAll. The file's size is not fixed. We have to copy the returned QByteArray to the vector<char> buffer.

What if I don't want this little overhead and want extreme fast file reading?

Would QFileDevice::map then memcpy be faster?

Should I use DataStream?

Or just plain read?

If plain read is preferred, then please criticize and tell me why the piece of code that i came up with maybe stupid :)

Why should the chunk_size be 1024? I saw many different values based on public codes.

Also Can I read the file's content directly into the vector<char>?

    QFile f("what.txt");

    std::vector<char> target;
    int chunk_size = 1024;
    QByteArray buffer;

    f.open(QIODevice::ReadOnly);

    while (!f.atEnd()) {
        buffer = f.read(chunk_size);
        target.insert(target.end(), buffer.cbegin(), buffer.cend());
    }

    f.close();

Thanks for your help!

Christian Ehrlicher

Use QFile::read(char* qint64).