DOC: Avoid GDI Object Private Clipboard Formats (89119)

SUMMARY

In the Microsoft Windows Software Development Kit (SDK) version 3.1 "Programmer's Reference Volume 2: Functions," page 828 of the documentation for the SetClipboardData function states:

Private data formats in the range CF_GDIOBJFIRST through CF_GDIOBJLAST will be automatically removed by a call to the DeleteObject function when the data is removed from the clipboard.

This statement is incorrect under Windows 3.1. Private data formats with types in this range are treated like global memory handles by Windows. As such, this range of private data formats should be avoided.

MORE INFORMATION

Under the debugging version of Windows, if an application calls the SetClipboardData function with a handle to a GDI object, and a format identifier in the range CF_GDIOBJFIRST through CF_GDIOBJLAST, Windows will output the following message on the debugging terminal:

err APPNAMEHERE->USER GLOBALREALLOC+15: Invalid global handle: 0x1234

This is due to a problem in Windows version 3.1. Windows treats the GDI object's handle as a global memory handle, when it should treat it as a GDI handle (for example, a handle to a brush, palette, font, and so on.)

In addition, the object will not be deleted properly when the EmptyClipboard function is called. This leads to a loss of memory in GDI's heap. When GDI's heap is exhausted, either Windows crashes or output is corrupted.