一个是句柄，一个是对象。 CDC::CreateCompatibleDC  virtual BOOL CreateCompatibleDC( CDC* pDC ); Return Value Nonzero if the function is successful; otherwise 0. 重要的在这 It can be used to prepare images in memory before copying them to the actual device surface of the compatible device. 可以进行图像缓冲 When a memory device context is created, GDI automatically selects a 1-by-1 monochrome stock bitmap for it. GDI output functions can be used with a memory device context only if a bitmap has been created and selected into that context. 只有图像被作为资源引入并选入该容器，GDI导出函数才可能被使用。 原来是操作GDI的利器  

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