Subclass QIODevice to allow saving an image into a std::vector<char>.

README.md

Subclass QIODevice to allow saving an image into a std::vector<char>. It can be useful for example when using cv::imdecode.

Usage:

QImage src("myImage.png");
CharVectorDevice myIODevice;
src.save(&myIODevice, "PNG", 100);

CharVectorDevice.h

#include <QIODevice>
#include <vector>
#include <algorithm>

struct CharVectorDevice : public QIODevice
{
public:
    virtual bool seek(qint64 pos)
    {
        if (pos < 0 || pos > static_cast<qint64>(m_vector.size())) {
            qWarning("CharVectorDevice::seek: Invalid pos: %d", int(pos));
            return false;
        }

        m_ioIndex = static_cast<int>(pos);
        return QIODevice::seek(pos);
    }

    std::vector<char>& GetVector()
    {
        return m_vector;
    }

protected:
    virtual qint64 readData(char *data, qint64 len)
    {
        if ((len = qMin(len, static_cast<qint64>(m_vector.size()) - m_ioIndex))
            <= 0) {
            return qint64(0);
        }
        std::copy(m_vector.cbegin() + m_ioIndex, m_vector.cbegin() + len, data);
        m_ioIndex += static_cast<int>(len);
        return len;
    }

    virtual qint64 writeData(const char *data, qint64 len)
    {
        const int overflow = static_cast
            <int>(m_ioIndex + len - m_vector.size());
        if (overflow > 0) {
            m_vector.resize(m_ioIndex + len);
        }

        std::copy(data, data + len, m_vector.begin() + m_ioIndex);
        m_ioIndex += static_cast<int>(len);

        return len;
    }

    int m_ioIndex;
    std::vector<char> m_vector;
};