cpp.info: Environment Variables

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Environment Variables

   This section describes the environment variables that affect how CPP
operates.  You can use them to specify directories or prefixes to use
when searching for include files, or to control dependency output.
   Note that you can also specify places to search using options such as
`-I', and control dependency output with options like `-M' (*note
Invocation::).  These take precedence over environment variables, which
in turn take precedence over the configuration of GCC.
`CPATH'
`C_INCLUDE_PATH'
`CPLUS_INCLUDE_PATH'
`OBJC_INCLUDE_PATH'
     Each variable's value is a list of directories separated by a
     special character, much like `PATH', in which to look for header
     files.  The special character, `PATH_SEPARATOR', is
     target-dependent and determined at GCC build time.  For
     Windows-based targets it is a semicolon, and for almost all other
     targets it is a colon.
     `CPATH' specifies a list of directories to be searched as if
     specified with `-I', but after any paths given with `-I' options
     on the command line.  The environment variable is used regardless
     of which language is being preprocessed.
     The remaining environment variables apply only when preprocessing
     the particular language indicated.  Each specifies a list of
     directories to be searched as if specified with `-isystem', but
     after any paths given with `-isystem' options on the command line.
     See also *Note Search Path::.
`DEPENDENCIES_OUTPUT'
     If this variable is set, its value specifies how to output
     dependencies for Make based on the non-system header files
     processed by the compiler.  System header files are ignored in the
     dependency output.
     The value of `DEPENDENCIES_OUTPUT' can be just a file name, in
     which case the Make rules are written to that file, guessing the
     target name from the source file name.  Or the value can have the
     form `FILE TARGET', in which case the rules are written to file
     FILE using TARGET as the target name.
     In other words, this environment variable is equivalent to
     combining the options `-MM' and `-MF' (*note Invocation::), with
     an optional `-MT' switch too.
`SUNPRO_DEPENDENCIES'
     This variable is the same as the environment variable
     `DEPENDENCIES_OUTPUT' (*note DEPENDENCIES_OUTPUT::), except that
     system header files are not ignored, so it implies `-M' rather
     than `-MM'.  However, the dependence on the main input file is
     omitted.  *Note Invocation::.