Adds the specified directory to the list of places that are searched for included files. The directories are searched in the order they are given, by multiple -I options. The in-memory file system is specified by -I-.

Uses Kernighan and Ritchie search rules for locating included files. The current place is defined by the original source file and is not stacked. See The current place for more information. If you do not use this option, Berkeley-style searching is used.

Makes the handling of quoted include files the same as angle-bracketed include files. Specifically, the current place is excluded from the search path.

Adds the specified comma-separated list of directories to the end of the search path, after all directories specified by -I options. Use -j- to search the in-memory file system.