ID Number: Q74291
3.00 3.10
WINDOWS
Summary:
The Microsoft Windows graphical environment maintains an internal
cache of five display contexts (DCs) which are shared by all
applications in the system. An application retrieves one of these DCs
when it calls the BeginPaint, GetDC, or GetWindowDC functions. When an
application retrieves a DC, Windows marks the DC as in use and does
not allow another application to retrieve it. When an application has
finished using a DC, it must return the DC to the cache which makes
the DC available to another application. Two functions return a DC to
the cache: the EndPaint function (to match BeginPaint) and the
ReleaseDC function (to match GetDC or GetWindowDC).
If an application fails to return DCs to the DC cache correctly, the
cache becomes empty, and subsequent calls to BeginPaint, GetDC, and
GetWindowDC fail. Because most applications do not check to be sure
that the DC they retrieve is valid, they attempt to use an invalid DC
in a graphics device interface (GDI) call, which causes a FatalExit
error.
To avoid this problem, be sure to return DCs to the cache correctly
and check the value returned by BeginPaint, GetDC, and GetWindowDC to
ensure that a valid DC is available.
Additional reference words: 3.00 3.10