QT5 QList<QImage> 中后面数据将前面数据覆盖问题的解决方案

最新推荐文章于 2025-01-06 20:50:07 发布

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最新推荐文章于 2025-01-06 20:50:07 发布 · 3.5k 阅读

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#qt5 #c++

QT5的隐式共享机制在参数传递时提高了效率，但可能导致QList<QImage>中数据被覆盖。问题在于QList添加的是QImage对象的引用，而非深拷贝。解决办法是在append前使用detach()方法确保每次添加的都是独立的数据副本。

QT5 中有一个Implicit Sharing的概念，叫做隐式共享，许多QT中许多C++类用隐式数据共享来减少copy带来的资源占用问题。

当作为参数传递时，隐式数据共享是安全和高效的，因为仅仅是指向数据的指针进行传递，而数据只在有函数对它进行改写是才进行复制。（copy on write）

QT的如下类均用到了这个机理，如果不希望进行隐式共享，则需要多加注意了。

QDBusPendingCall	The QDBusPendingCall class refers to one pending asynchronous call
QDBusUnixFileDescriptor	The QDBusUnixFileDescriptor class holds one Unix file descriptor.
QBitmap	The QBitmap class provides monochrome (1-bit depth) pixmaps.
QIcon	The QIcon class provides scalable icons in different modes and states.
QImage	The QImage class provides a hardware-independent image representation that allows direct access to the pixel data, and can be used as a paint device.
QPicture	The QPicture class is a paint device that records and replays QPainter commands.
QPixmap	The QPixmap class is an off-screen image representation that can be used as a paint device.
QCursor	The QCursor class provides a mouse cursor with an arbitrary shape.
QKeySequence	The QKeySequence class encapsulates a key sequence as used by shortcuts.
QPalette	The QPalette class contains color groups for each widget state.
QOpenGLDebugMessage	The QOpenGLDebugMessage class wraps an OpenGL debug message.
QBrush	The QBrush class defines the fill pattern of shapes drawn by QPainter.
QGradient	The QGradient class is used in combination with QBrush to specify gradient fills.
QPainterPath	The QPainterPath class provides a container for painting operations, enabling graphical shapes to be constructed and reused.
QPen	The QPen class defines how a QPainter should draw lines and outlines of shapes.
QPolygon	The QPolygon class provides a vector of points using integer precision.
QPolygonF	The QPolygonF class provides a vector of points using floating point precision.
QRegion	The QRegion class specifies a clip region for a painter.