invoke.texi

理解和实践操作系统的一本好书

Ada source code file containing a library unit body (a subprogram or
package body).  Such files are also called @dfn{bodies}.

@c GCC also knows about some suffixes for languages not yet included:
@c Pascal:
@c @var{file}.p
@c @var{file}.pas
@c Ratfor:
@c @var{file}.r

@item @var{file}.s
Assembler code.

@item @var{file}.S
@itemx @var{file}.sx
Assembler code which must be preprocessed.

@item @var{other}
An object file to be fed straight into linking.
Any file name with no recognized suffix is treated this way.
@end table

@opindex x
You can specify the input language explicitly with the @option{-x} option:

@table @gcctabopt
@item -x @var{language}
Specify explicitly the @var{language} for the following input files
(rather than letting the compiler choose a default based on the file
name suffix).  This option applies to all following input files until
the next @option{-x} option.  Possible values for @var{language} are:
@smallexample
c  c-header  c-cpp-output
c++  c++-header  c++-cpp-output
objective-c  objective-c-header  objective-c-cpp-output
objective-c++ objective-c++-header objective-c++-cpp-output
assembler  assembler-with-cpp
ada
f95  f95-cpp-input
java
treelang
@end smallexample

@item -x none
Turn off any specification of a language, so that subsequent files are
handled according to their file name suffixes (as they are if @option{-x}
has not been used at all).

@item -pass-exit-codes
@opindex pass-exit-codes
Normally the @command{gcc} program will exit with the code of 1 if any
phase of the compiler returns a non-success return code.  If you specify
@option{-pass-exit-codes}, the @command{gcc} program will instead return with
numerically highest error produced by any phase that returned an error
indication.  The C, C++, and Fortran frontends return 4, if an internal
compiler error is encountered.
@end table

If you only want some of the stages of compilation, you can use
@option{-x} (or filename suffixes) to tell @command{gcc} where to start, and
one of the options @option{-c}, @option{-S}, or @option{-E} to say where
@command{gcc} is to stop.  Note that some combinations (for example,
@samp{-x cpp-output -E}) instruct @command{gcc} to do nothing at all.

@table @gcctabopt
@item -c
@opindex c
Compile or assemble the source files, but do not link.  The linking
stage simply is not done.  The ultimate output is in the form of an
object file for each source file.

By default, the object file name for a source file is made by replacing
the suffix @samp{.c}, @samp{.i}, @samp{.s}, etc., with @samp{.o}.

Unrecognized input files, not requiring compilation or assembly, are
ignored.

@item -S
@opindex S
Stop after the stage of compilation proper; do not assemble.  The output
is in the form of an assembler code file for each non-assembler input
file specified.

By default, the assembler file name for a source file is made by
replacing the suffix @samp{.c}, @samp{.i}, etc., with @samp{.s}.

Input files that don't require compilation are ignored.

@item -E
@opindex E
Stop after the preprocessing stage; do not run the compiler proper.  The
output is in the form of preprocessed source code, which is sent to the
standard output.

Input files which don't require preprocessing are ignored.

@cindex output file option
@item -o @var{file}
@opindex o
Place output in file @var{file}.  This applies regardless to whatever
sort of output is being produced, whether it be an executable file,
an object file, an assembler file or preprocessed C code.

If @option{-o} is not specified, the default is to put an executable
file in @file{a.out}, the object file for
@file{@var{source}.@var{suffix}} in @file{@var{source}.o}, its
assembler file in @file{@var{source}.s}, a precompiled header file in
@file{@var{source}.@var{suffix}.gch}, and all preprocessed C source on
standard output.

@item -v
@opindex v
Print (on standard error output) the commands executed to run the stages
of compilation.  Also print the version number of the compiler driver
program and of the preprocessor and the compiler proper.

@item -###
@opindex ###
Like @option{-v} except the commands are not executed and all command
arguments are quoted.  This is useful for shell scripts to capture the
driver-generated command lines.

@item -pipe
@opindex pipe
Use pipes rather than temporary files for communication between the
various stages of compilation.  This fails to work on some systems where
the assembler is unable to read from a pipe; but the GNU assembler has
no trouble.

@item -combine
@opindex combine
If you are compiling multiple source files, this option tells the driver
to pass all the source files to the compiler at once (for those
languages for which the compiler can handle this).  This will allow
intermodule analysis (IMA) to be performed by the compiler.  Currently the only
language for which this is supported is C@.  If you pass source files for
multiple languages to the driver, using this option, the driver will invoke
the compiler(s) that support IMA once each, passing each compiler all the
source files appropriate for it.  For those languages that do not support
IMA this option will be ignored, and the compiler will be invoked once for
each source file in that language.  If you use this option in conjunction
with @option{-save-temps}, the compiler will generate multiple
pre-processed files
(one for each source file), but only one (combined) @file{.o} or
@file{.s} file.

@item --help
@opindex help
Print (on the standard output) a description of the command line options
understood by @command{gcc}.  If the @option{-v} option is also specified
then @option{--help} will also be passed on to the various processes
invoked by @command{gcc}, so that they can display the command line options
they accept.  If the @option{-Wextra} option has also been specified
(prior to the @option{--help} option), then command line options which
have no documentation associated with them will also be displayed.

@item --target-help
@opindex target-help
Print (on the standard output) a description of target-specific command
line options for each tool.  For some targets extra target-specific
information may also be printed.

@item --help=@var{class}@r{[},@var{qualifier}@r{]}
Print (on the standard output) a description of the command line
options understood by the compiler that fit into a specific class.
The class can be one of @samp{optimizers}, @samp{warnings}, @samp{target},
@samp{params}, or @var{language}:

@table @asis
@item @samp{optimizers}
This will display all of the optimization options supported by the
compiler.

@item @samp{warnings}
This will display all of the options controlling warning messages
produced by the compiler.

@item @samp{target}
This will display target-specific options.  Unlike the
@option{--target-help} option however, target-specific options of the
linker and assembler will not be displayed.  This is because those
tools do not currently support the extended @option{--help=} syntax.

@item @samp{params}
This will display the values recognized by the @option{--param}
option.

@item @var{language}
This will display the options supported for @var{language}, where 
@var{language} is the name of one of the languages supported in this 
version of GCC.

@item @samp{common}
This will display the options that are common to all languages.
@end table

It is possible to further refine the output of the @option{--help=}
option by adding a comma separated list of qualifiers after the
class.  These can be any from the following list:

@table @asis
@item @samp{undocumented}
Display only those options which are undocumented.

@item @samp{joined}
Display options which take an argument that appears after an equal
sign in the same continuous piece of text, such as:
@samp{--help=target}.

@item @samp{separate}
Display options which take an argument that appears as a separate word
following the original option, such as: @samp{-o output-file}.
@end table

Thus for example to display all the undocumented target-specific
switches supported by the compiler the following can be used:

@smallexample
--help=target,undocumented
@end smallexample

The sense of a qualifier can be inverted by prefixing it with the
@var{^} character, so for example to display all binary warning
options (i.e., ones that are either on or off and that do not take an
argument), which have a description the following can be used:

@smallexample
--help=warnings,^joined,^undocumented
@end smallexample

A class can also be used as a qualifier, although this usually
restricts the output by so much that there is nothing to display.  One
case where it does work however is when one of the classes is
@var{target}.  So for example to display all the target-specific
optimization options the following can be used:

@smallexample
--help=target,optimizers
@end smallexample

The @option{--help=} option can be repeated on the command line.  Each
successive use will display its requested class of options, skipping
those that have already been displayed.

If the @option{-Q} option appears on the command line before the
@option{--help=} option, then the descriptive text displayed by
@option{--help=} is changed.  Instead of describing the displayed
options, an indication is given as to whether the option is enabled,
disabled or set to a specific value (assuming that the compiler
knows this at the point where the @option{--help=} option is used).

Here is a truncated example from the ARM port of @command{gcc}:

@smallexample
  % gcc -Q -mabi=2 --help=target -c
  The following options are target specific:
  -mabi=                                2
  -mabort-on-noreturn                   [disabled]
  -mapcs                                [disabled]
@end smallexample

The output is sensitive to the effects of previous command line
options, so for example it is possible to find out which optimizations
are enabled at @option{-O2} by using:

@smallexample
-O2 --help=optimizers
@end smallexample

Alternatively you can discover which binary optimizations are enabled
by @option{-O3} by using:

@smallexample
gcc -c -Q -O3 --help=optimizers > /tmp/O3-opts
gcc -c -Q -O2 --help=optimizers > /tmp/O2-opts
diff /tmp/O2-opts /tmp/O3-opts | grep enabled
@end smallexample

@item --version
@opindex version
Display the version number and copyrights of the invoked GCC@.

@include @value{srcdir}/../libiberty/at-file.texi
@end table

@node Invoking G++
@section Compiling C++ Programs

@cindex suffixes for C++ source
@cindex C++ source file suffixes
C++ source files conventionally use one of the suffixes @samp{.C},
@samp{.cc}, @samp{.cpp}, @samp{.CPP}, @samp{.c++}, @samp{.cp}, or
@samp{.cxx}; C++ header files often use @samp{.hh}, @samp{.hpp},
@samp{.H}, or (for shared template code) @samp{.tcc}; and
preprocessed C++ files use the suffix @samp{.ii}.  GCC recognizes
files with these names and compiles them as C++ programs even if you
call the compiler the same way as for compiling C programs (usually
with the name @command{gcc}).

@findex g++
@findex c++
However, the use of @command{gcc} does not add the C++ library.
@command{g++} is a program that calls GCC and treats @samp{.c},
@samp{.h} and @samp{.i} files as C++ source files instead of C source
files unless @option{-x} is used, and automatically specifies linking
against the C++ library.  This program is also useful when
precompiling a C header file with a @samp{.h} extension for use in C++
compilations.  On many systems, @command{g++} is also installed with
the name @command{c++}.

@cindex invoking @command{g++}
When you compile C++ programs, you may specify many of the same
command-line options that you use for compiling programs in any
language; or command-line options meaningful for C and related
languages; or options that are meaningful only for C++ programs.
@xref{C Dialect Options,,Options Controlling C Dialect}, for
explanations of options for languages related to C@.
@xref{C++ Dialect Options,,Options Controlling C++ Dialect}, for
explanations of options that are meaningful only for C++ programs.