Question

Programming with C++, once we get the context device by GetDC to use. What bad things may happen if we exit the program without calling to ReleaseDC?

Answer 1

From the docs

The ReleaseDC function releases a device context (DC), freeing it for
use by other applications. The effect of the ReleaseDC function
depends on the type of DC. It frees only common and window DCs. It has
no effect on class or private DCs.

As you can see, it may be needed if other applications can access the same DC.

In any case, it’s good idea to use C++ RAII idiom for this kind of things. Consider this class:

class ScopedDC
{
   public:
      ScopedDC(HDC handle):handle(handle){}
      ~ScopedDC() { ReleaseDC(handle); }
      HDC get() const {return handle; }
   //disable copying. Same can be achieved by deriving from boost::noncopyable
   private:
      ScopedDC(const ScopedDC&);
      ScopedDC& operator = (const ScopedDC&); 

   private:
      HDC handle;
};

With this class you can do this:

{
   ScopedDC dc(GetDC());
   //do stuff with dc.get();
}  //DC is automatically released here, even in case of exceptions