ReleaseDC

ReleaseDC is a Windows API function that releases a device context (DC) previously obtained with GetDC or GetWindowDC. It is used to return the DC to the system when drawing to a window or the screen is finished, so that GDI resources can be reused.

The function prototype is int ReleaseDC(HWND hWnd, HDC hDC). The hWnd parameter should be the window associated with the DC being released. If the DC was obtained for the entire screen using GetDC(NULL), you should pass NULL for hWnd. After calling ReleaseDC, the DC handle is no longer valid for use.

The return value indicates success or failure: a nonzero value indicates success, while zero indicates failure. In case of failure, diagnostic information may be obtained via GetLastError. It is important to pair each successful GetDC or GetWindowDC with a corresponding ReleaseDC to avoid leaking GDI resources.

Important caveat: DCs obtained through BeginPaint during WM_PAINT processing should not be released with ReleaseDC; they must be released with EndPaint. ReleaseDC is intended for DCs obtained outside the paint cycle.

Related functions include GetDC, GetWindowDC, EndPaint, and BeginPaint. In typical usage, code obtains a DC for drawing, performs rendering, and then releases the DC with ReleaseDC, for example: HDC hdc = GetDC(hwnd); /* drawing operations */ ReleaseDC(hwnd, hdc);