

3.15 Options for Directory Search


-I dir
-iquote dir
-isystem dir
-idirafter dir

Add the directory dir to the list of directories to be searched for header files during preprocessing. If dir begins with ‘=’ or $SYSROOT, then the ‘=’ or $SYSROOT is replaced by the sysroot prefix; see --sysroot and -isysroot.

Directories specified with -iquote apply only to the quote form of the directive, #include "file". Directories specified with -I, -isystem, or -idirafter apply to lookup for both the #include "file" and #include <file> directives.


  5. Standard system directories are scanned.



If a standard system include directory, or a directory specified with -isystem, is also specified with -I, the -I option is ignored. The directory is still searched but as a system directory at its normal position in the system include chain. This is to ensure that GCC’s procedure to fix buggy system headers and the ordering for the #include_next directive are not inadvertently changed. If you really need to change the search order for system directories, use the -nostdinc and/or -isystem options.





-iprefix prefix

Specify prefix as the prefix for subsequent -iwithprefix options. If the prefix represents a directory, you should include the final ‘/’.

-iwithprefix dir
-iwithprefixbefore dir


-isysroot dir


-imultilib dir







Set the directory to search for plugins that are passed by -fplugin=name instead of -fplugin=path/ This option is not meant to be used by the user, but only passed by the driver.





The compiler driver program runs one or more of the subprograms cpp, cc1, as and ld. It tries prefix as a prefix for each program it tries to run, both with and without ‘machine/version/’ for the corresponding target machine and compiler version.

For each subprogram to be run, the compiler driver first tries the -B prefix, if any. If that name is not found, or if -B is not specified, the driver tries two standard prefixes, /usr/lib/gcc/ and /usr/local/lib/gcc/. If neither of those results in a file name that is found, the unmodified program name is searched for using the directories specified in your PATH environment variable.

The compiler checks to see if the path provided by -B refers to a directory, and if necessary it adds a directory separator character at the end of the path.

-B prefixes that effectively specify directory names also apply to libraries in the linker, because the compiler translates these options into -L options for the linker. They also apply to include files in the preprocessor, because the compiler translates these options into -isystem options for the preprocessor. In this case, the compiler appends ‘include’ to the prefix.



As a special kludge, if the path provided by -B is [dir/]stageN/, where N is a number in the range 0 to 9, then it is replaced by [dir/]include. This is to help with boot-strapping the compiler.


Do not expand any symbolic links, resolve references to ‘/../’ or ‘/./’, or make the path absolute when generating a relative prefix.


Use dir as the logical root directory for headers and libraries. For example, if the compiler normally searches for headers in /usr/include and libraries in /usr/lib, it instead searches dir/usr/include and dir/usr/lib.

If you use both this option and the -isysroot option, then the --sysroot option applies to libraries, but the -isysroot option applies to header files.

The GNU linker (beginning with version 2.16) has the necessary support for this option. If your linker does not support this option, the header file aspect of --sysroot still works, but the library aspect does not.


For some targets, a suffix is added to the root directory specified with --sysroot, depending on the other options used, so that headers may for example be found in dir/suffix/usr/include instead of dir/usr/include. This option disables the addition of such a suffix.
