The file type is key to determining how Source Insight treats a file. Most importantly, it controls what programming language is associated with each file. A file type also specifies editing and display options, such as the tab width, word wrap, auto-indentation, display font, and others.
To see what file type is associated with the current file, right-click on the source file window and select File Type Options. The file's current file type is automatically selected in the dialog box.