int EnumObjects( int nObjectType, int ( FAR PASCAL EXPORT* lpfn )( LPSTR, LPSTR ), LPSTR lpData );
nObjectType
Specifies the object type. It can have the values OBJ_BRUSH or OBJ_PEN.
lpfn
Is the procedure-instance address of the application-supplied callback function. See the “Remarks” section below.
lpData
Points to the application-supplied data. The data is passed to the callback function along with the object information.
Enumerates the pens and brushes available in a device context. For each object of a given type, the callback function that you pass is called with the information for that object. The system calls the callback function until there are no more objects or the callback function returns 0.
Note that new features of Microsoft C/C++ let you use an ordinary function as the function passed to EnumObjects. The address passed to EnumObjects is a FAR pointer to a function exported with __export and with the Pascal calling convention. In protect-mode applications, you do not have to create this function with the Windows MakeProcInstance function or free the function after use with FreeProcInstance.
You also do not have to export the function name in an EXPORTS statement in your application's module-definition file. You can instead use the __export function modifier, as in
int FAR PASCAL __export AFunction( LPSTR, LPSTR );
to cause the compiler to emit the proper export record for export by name without aliasing. This works for most needs. For some special cases, such as exporting a function by ordinal or aliasing the export, you still need to use an EXPORTS statement in a module-definition file.
For compiling Foundation programs, you'll normally use the /GA and /GEs compiler options. The /Gw compiler option is not used with the Foundation classes. (If you do use MakeProcInstance, you will need to explicitly cast the returned function pointer from FARPROC to the type needed in this API.) Callback registration interfaces are now type-safe (you must pass in a function pointer that points to the right kind of function for the specific callback).
Also note that all callback functions must trap Foundation exceptions before returning to Windows, since exceptions cannot be thrown across callback boundaries. For more information about exceptions, see Chapter 12 in the Class Libraries User's Guide.