There are several ways to search across multiple files in Source Insight. The commands: Search Files, Lookup References, and Search Project all perform multi-file searches.
The fastest type of search in Source Insight is the Lookup References search. When you search this way, Source Insight looks for references to a single whole-word item. When you search for a single whole-word, Source Insight uses a special index file to make the search fast. It’s a good idea to get into the habit of using Lookup References, instead of Search Files, when you can.