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
(see 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
PATH
, in which to look for header files. The special character, PATH_SEPARATOR
, is target-dependent and determined at GCC build time. For Microsoft 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. This 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.
In all these variables, an empty element instructs the compiler to search its current working directory. Empty elements can appear at the beginning or end of a path. For instance, if the value of CPATH
is :/special/include
, that has the same effect as ‘-I. -I/special/include
’.
See also Search Path.
DEPENDENCIES_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
(see Invocation), with an optional -MT
switch too.
SUNPRO_DEPENDENCIES
DEPENDENCIES_OUTPUT
(see above), 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. See Invocation.
© Free Software Foundation
Licensed under the GNU Free Documentation License, Version 1.3.
https://gcc.gnu.org/onlinedocs/gcc-4.9.3/cpp/Environment-Variables.html