B.2.34 -I[-|dir]

-I dir adds dir to the list of directories that are searched for #include files with relative file names prior to /usr/include, that is, those directory paths not beginning with a / (slash).

Directories for multiple -I options are searched in the order specified.

For more information on the search pattern of the compiler, see 2.14.1 Using the -I- Option to Change the Search Algorithm.