Environment Variables Affecting GCC
===================================
This section describes several environment variables that affect how
GCC operates. Some of them work by specifying directories or prefixes
to use when searching for various kinds of files. Some are used to
specify other aspects of the compilation environment.
Note that you can also specify places to search using options such as
`-B', `-I' and `-L' (Note:Directory Options). These take precedence
over places specified using environment variables, which in turn take
precedence over those specified by the configuration of GCC. Note:Driver.
`LANG'
`LC_CTYPE'
`LC_MESSAGES'
`LC_ALL'
These environment variables control the way that GCC uses
localization information that allow GCC to work with different
national conventions. GCC inspects the locale categories
`LC_CTYPE' and `LC_MESSAGES' if it has been configured to do so.
These locale categories can be set to any value supported by your
installation. A typical value is `en_UK' for English in the United
Kingdom.
The `LC_CTYPE' environment variable specifies character
classification. GCC uses it to determine the character boundaries
in a string; this is needed for some multibyte encodings that
contain quote and escape characters that would otherwise be
interpreted as a string end or escape.
The `LC_MESSAGES' environment variable specifies the language to
use in diagnostic messages.
If the `LC_ALL' environment variable is set, it overrides the value
of `LC_CTYPE' and `LC_MESSAGES'; otherwise, `LC_CTYPE' and
`LC_MESSAGES' default to the value of the `LANG' environment
variable. If none of these variables are set, GCC defaults to
traditional C English behavior.
`TMPDIR'
If `TMPDIR' is set, it specifies the directory to use for temporary
files. GCC uses temporary files to hold the output of one stage of
compilation which is to be used as input to the next stage: for
example, the output of the preprocessor, which is the input to the
compiler proper.
`GCC_EXEC_PREFIX'
If `GCC_EXEC_PREFIX' is set, it specifies a prefix to use in the
names of the subprograms executed by the compiler. No slash is
added when this prefix is combined with the name of a subprogram,
but you can specify a prefix that ends with a slash if you wish.
If `GCC_EXEC_PREFIX' is not set, GCC will attempt to figure out an
appropriate prefix to use based on the pathname it was invoked
with.
If GCC cannot find the subprogram using the specified prefix, it
tries looking in the usual places for the subprogram.
The default value of `GCC_EXEC_PREFIX' is `PREFIX/lib/gcc-lib/'
where PREFIX is the value of `prefix' when you ran the `configure'
script.
Other prefixes specified with `-B' take precedence over this
prefix.
This prefix is also used for finding files such as `crt0.o' that
are used for linking.
In addition, the prefix is used in an unusual way in finding the
directories to search for header files. For each of the standard
directories whose name normally begins with
`/usr/local/lib/gcc-lib' (more precisely, with the value of
`GCC_INCLUDE_DIR'), GCC tries replacing that beginning with the
specified prefix to produce an alternate directory name. Thus,
with `-Bfoo/', GCC will search `foo/bar' where it would normally
search `/usr/local/lib/bar'. These alternate directories are
searched first; the standard directories come next.
`COMPILER_PATH'
The value of `COMPILER_PATH' is a colon-separated list of
directories, much like `PATH'. GCC tries the directories thus
specified when searching for subprograms, if it can't find the
subprograms using `GCC_EXEC_PREFIX'.
`LIBRARY_PATH'
The value of `LIBRARY_PATH' is a colon-separated list of
directories, much like `PATH'. When configured as a native
compiler, GCC tries the directories thus specified when searching
for special linker files, if it can't find them using
`GCC_EXEC_PREFIX'. Linking using GCC also uses these directories
when searching for ordinary libraries for the `-l' option (but
directories specified with `-L' come first).
`C_INCLUDE_PATH'
`CPLUS_INCLUDE_PATH'
`OBJC_INCLUDE_PATH'
These environment variables pertain to particular languages. Each
variable's value is a colon-separated list of directories, much
like `PATH'. When GCC searches for header files, it tries the
directories listed in the variable for the language you are using,
after the directories specified with `-I' but before the standard
header file directories.
`DEPENDENCIES_OUTPUT'
If this variable is set, its value specifies how to output
dependencies for Make based on the header files processed by the
compiler. This output looks much like the output from the `-M'
option (Note:Preprocessor Options), but it goes to a separate
file, and is in addition to the usual results of compilation.
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.
`LANG'
This variable is used to pass locale information to the compiler.
One way in which this information is used is to determine the
character set to be used when character literals, string literals
and comments are parsed in C and C++. When the compiler is
configured to allow multibyte characters, the following values for
`LANG' are recognized:
`C-JIS'
Recognize JIS characters.
`C-SJIS'
Recognize SJIS characters.
`C-EUCJP'
Recognize EUCJP characters.
If `LANG' is not defined, or if it has some other value, then the
compiler will use mblen and mbtowc as defined by the default
locale to recognize and translate multibyte characters.