If NULL is passed for the pIconInfo parameter, the caller is asking for the size of the ICONINFO buffer needed for this class (usually for memory allocation purposes). Otherwise, the pIconInfo parameter can always be assumed to be large enough to accommodate the ICONINFO and the variable data for this class.

Note that the ICONINFO structure allows you to specify the default icon in three different ways:

• Block of binary data
  
• Icon file name
  
• Module name and resource identifier

However, only one mechanism need be supported by any given class. For example, a caller cannot request one of the three formats by prefilling the ICONINFO structure.