HDM_HITTEST Overview Group

The HDM_HITTEST message tests a point to determine which header item, if any, is at the specified point.

HDM_HITTEST 

wParam = 0; 

lParam = (LPARAM) (HD_HITTESTINFO FAR *) phdhti;

Parameters

phdhti: Pointer to an HD_HITTESTINFO structure that contains the position to test and receives information about the results of the test.

Returns the index of the item at the specified position, if any, or - 1 otherwise.