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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' (see Options for Directory Search).
- 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.
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 (which TIGCC is not),
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).
- 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.
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.
Some additional environments variables affect the behavior of the
preprocessor.
- CPATH
C_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.
C_INCLUDE_PATH
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
.
- 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'
(see Options Controlling the Preprocessor),
with an optional '-MT' switch, too.
- SUNPRO_DEPENDENCIES
- This variable is the same as
DEPENDENCIES_OUTPUT
(see above),
except that system header files are not ignored, so it implies
'-M' rather than '-MM'
(see Options Controlling the Preprocessor).
However, the dependence on the main input file is omitted.