Inside of QImage::QImage() Qt-5.7/5.7/Src/qtbase/src/gui/image/qimage.cpp

qimage.cpp

/*! \fn QImageData * QImageData::create(const QSize &size, QImage::Format format)

    \internal

    Creates a new image data.
    Returns 0 if invalid parameters are give or anything else failed.
*/
QImageData * QImageData::create(const QSize &size, QImage::Format format)
{
    if (!size.isValid() || format == QImage::Format_Invalid)
        return 0;                                // invalid parameter(s)

    uint width = size.width();
    uint height = size.height();
    uint depth = qt_depthForFormat(format);

    const int bytes_per_line = ((width * depth + 31) >> 5) << 2; // bytes per scanline (must be multiple of 4)

    // sanity check for potential overflows
    if (INT_MAX/depth < width
        || bytes_per_line <= 0
        || height <= 0
        || INT_MAX/uint(bytes_per_line) < height
        || INT_MAX/sizeof(uchar *) < uint(height))
        return 0;

    QScopedPointer<QImageData> d(new QImageData);

    switch (format) {
    case QImage::Format_Mono:
    case QImage::Format_MonoLSB:
        d->colortable.resize(2);
        d->colortable[0] = QColor(Qt::black).rgba();
        d->colortable[1] = QColor(Qt::white).rgba();
        break;
    default:
        break;
    }

    d->width = width;
    d->height = height;
    d->depth = depth;
    d->format = format;
    d->has_alpha_clut = false;
    d->is_cached = false;

    d->bytes_per_line = bytes_per_line;

    d->nbytes = d->bytes_per_line*height;
    d->data  = (uchar *)malloc(d->nbytes);

    if (!d->data) {
        return 0;
    }

    d->ref.ref();
    return d.take();

}