gcc.1

GCC编译器源代码

.B c\-header\c
\&\|', `\|\c
.B c++\c
\&\|',
`\|\c
.B cpp\-output\c
\&\|', `\|\c
.B assembler\c
\&\|', and `\|\c
.B assembler\-with\-cpp\c
\&\|'.
.TP
.B \-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 `\|\c
.B \-x\c
\&\|'
has not been used at all).
.PP
If you want only some of the four stages (preprocess, compile,
assemble, link), you can use
`\|\c
.B \-x\c
\&\|' (or filename suffixes) to tell \c
.B gcc\c
\& where to start, and
one of the options `\|\c
.B \-c\c
\&\|', `\|\c
.B \-S\c
\&\|', or `\|\c
.B \-E\c
\&\|' to say where
.B gcc\c
\& is to stop.  Note that some combinations (for example,
`\|\c
.B \-x cpp\-output \-E\c
\&\|') instruct \c
.B gcc\c
\& to do nothing at all.
.TP
.B \-c
Compile or assemble the source files, but do not link.  The compiler
output is an object file corresponding to each source file.
.Sp
By default, GCC makes the object file name for a source file by replacing
the suffix `\|\c
.B .c\c
\&\|', `\|\c
.B .i\c
\&\|', `\|\c
.B .s\c
\&\|', etc., with `\|\c
.B .o\c
\&\|'.  Use
.B \-o\c
\& to select another name.
.Sp
GCC ignores any unrecognized input files (those that do not require
compilation or assembly) with the
.B \-c
option.
.TP
.B \-S
Stop after the stage of compilation proper; do not assemble.  The output
is an assembler code file for each non-assembler input
file specified.
.Sp
By default, GCC makes the assembler file name for a source file by
replacing the suffix `\|\c
.B .c\c
\&\|', `\|\c
.B .i\c
\&\|', etc., with `\|\c
.B .s\c
\&\|'.  Use
.B \-o\c
\& to select another name.
.Sp
GCC ignores any input files that don't require compilation.
.TP
.B \-E
Stop after the preprocessing stage; do not run the compiler proper.  The
output is preprocessed source code, which is sent to the
standard output.
.Sp
GCC ignores input files which don't require preprocessing.
.TP
.BI "\-o " file
Place output in file \c
.I file\c
\&.  This applies regardless to whatever
sort of output GCC is producing, whether it be an executable file,
an object file, an assembler file or preprocessed C code.
.Sp
Since only one output file can be specified, it does not make sense to
use `\|\c
.B \-o\c
\&\|' when compiling more than one input file, unless you are
producing an executable file as output.
.Sp
If you do not specify `\|\c
.B \-o\c
\&\|', the default is to put an executable file
in `\|\c
.B a.out\c
\&\|', the object file for `\|\c
.I source\c
.B \&.\c
.I suffix\c
\&\c
\&\|' in
`\|\c
.I source\c
.B \&.o\c
\&\|', its assembler file in `\|\c
.I source\c
.B \&.s\c
\&\|', and
all preprocessed C source on standard output.
.TP
.B \-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.
.TP
.B \-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 cannot read from a pipe; but the GNU assembler has
no trouble.
.PP
.SH LANGUAGE OPTIONS
The following options control the dialect of C that the compiler
accepts:
.TP
.B \-ansi
Support all ANSI standard C programs.
.Sp
This turns off certain features of GNU C that are incompatible with
ANSI C, such as the \c
.B asm\c
\&, \c
.B inline\c
\& and \c
.B typeof
keywords, and predefined macros such as \c
.B unix\c
\& and \c
.B vax
that identify the type of system you are using.  It also enables the
undesirable and rarely used ANSI trigraph feature, and disallows `\|\c
.B $\c
\&\|' as part of identifiers.
.Sp
The alternate keywords \c
.B _\|_asm_\|_\c
\&, \c
.B _\|_extension_\|_\c
\&,
.B _\|_inline_\|_\c
\& and \c
.B _\|_typeof_\|_\c
\& continue to work despite
`\|\c
.B \-ansi\c
\&\|'.  You would not want to use them in an ANSI C program, of
course, but it is useful to put them in header files that might be included
in compilations done with `\|\c
.B \-ansi\c
\&\|'.  Alternate predefined macros
such as \c
.B _\|_unix_\|_\c
\& and \c
.B _\|_vax_\|_\c
\& are also available, with or
without `\|\c
.B \-ansi\c
\&\|'.
.Sp
The `\|\c
.B \-ansi\c
\&\|' option does not cause non-ANSI programs to be
rejected gratuitously.  For that, `\|\c
.B \-pedantic\c
\&\|' is required in
addition to `\|\c
.B \-ansi\c
\&\|'.
.Sp
The preprocessor predefines a macro \c
.B _\|_STRICT_ANSI_\|_\c
\& when you use the `\|\c
.B \-ansi\c
\&\|'
option.  Some header files may notice this macro and refrain
from declaring certain functions or defining certain macros that the
ANSI standard doesn't call for; this is to avoid interfering with any
programs that might use these names for other things.
.TP
.B \-fno\-asm
Do not recognize \c
.B asm\c
\&, \c
.B inline\c
\& or \c
.B typeof\c
\& as a
keyword.  These words may then be used as identifiers.  You can
use \c
.B _\|_asm_\|_\c
\&, \c
.B _\|_inline_\|_\c
\& and \c
.B _\|_typeof_\|_\c
\& instead.
`\|\c
.B \-ansi\c
\&\|' implies `\|\c
.B \-fno\-asm\c
\&\|'.
.TP
.B \-fno\-builtin
Don't recognize built-in functions that do not begin with two leading
underscores.  Currently, the functions affected include \c
.B _exit\c
\&,
.B abort\c
\&, \c
.B abs\c
\&, \c
.B alloca\c
\&, \c
.B cos\c
\&, \c
.B exit\c
\&,
.B fabs\c
\&, \c
.B labs\c
\&, \c
.B memcmp\c
\&, \c
.B memcpy\c
\&, \c
.B sin\c
\&,
.B sqrt\c
\&, \c
.B strcmp\c
\&, \c
.B strcpy\c
\&, and \c
.B strlen\c
\&.
.Sp
The `\|\c
.B \-ansi\c
\&\|' option prevents \c
.B alloca\c
\& and \c
.B _exit\c
\& from
being builtin functions.
.TP
.B \-fhosted
Compile for a hosted environment; this implies the `\|\c
.B \-fbuiltin\c
\&\|' option, and implies that suspicious declarations of
.B main\c
\& should be warned about.
.TP
.B \-ffreestanding
Compile for a freestanding environment; this implies the `\|\c
.B \-fno-builtin\c
\&\|' option, and implies that
.B main\c
\& has no special requirements.
.TP
.B \-fno\-strict\-prototype
Treat a function declaration with no arguments, such as `\|\c
.B int foo
();\c
\&\|', as C would treat it\(em\&as saying nothing about the number of
arguments or their types (C++ only).  Normally, such a declaration in
C++ means that the function \c
.B foo\c
\& takes no arguments.
.TP
.B \-trigraphs
Support ANSI C trigraphs.  The `\|\c
.B \-ansi\c
\&\|' option implies `\|\c
.B \-trigraphs\c
\&\|'.
.TP
.B \-traditional
Attempt to support some aspects of traditional C compilers.
For details, see the GNU C Manual; the duplicate list here
has been deleted so that we won't get complaints when it
is out of date.
.Sp
But one note about C++ programs only (not C).  `\|\c
.B \-traditional\c
\&\|' has one additional effect for C++: assignment to
.B this
is permitted.  This is the same as the effect of `\|\c
.B \-fthis\-is\-variable\c
\&\|'.
.TP
.B \-traditional\-cpp
Attempt to support some aspects of traditional C preprocessors.
This includes the items that specifically mention the preprocessor above,
but none of the other effects of `\|\c
.B \-traditional\c
\&\|'.
.TP
.B \-fdollars\-in\-identifiers
Permit the use of `\|\c
.B $\c
\&\|' in identifiers (C++ only).  You can also use
`\|\c
.B \-fno\-dollars\-in\-identifiers\c
\&\|' to explicitly prohibit use of
`\|\c
.B $\c
\&\|'.  (GNU C++ allows `\|\c
.B $\c
\&\|' by default on some target systems
but not others.)
.TP
.B \-fenum\-int\-equiv
Permit implicit conversion of \c
.B int\c
\& to enumeration types (C++
only).  Normally GNU C++ allows conversion of \c
.B enum\c
\& to \c
.B int\c
\&,
but not the other way around.
.TP
.B \-fexternal\-templates
Produce smaller code for template declarations, by generating only a
single copy of each template function where it is defined (C++ only).
To use this option successfully, you must also mark all files that
use templates with either `\|\c
.B #pragma implementation\c
\&\|' (the definition) or
`\|\c
.B #pragma interface\c
\&\|' (declarations).

When your code is compiled with `\|\c
.B \-fexternal\-templates\c
\&\|', all
template instantiations are external.  You must arrange for all
necessary instantiations to appear in the implementation file; you can
do this with a \c
.B typedef\c
\& that references each instantiation needed.
Conversely, when you compile using the default option
`\|\c
.B \-fno\-external\-templates\c
\&\|', all template instantiations are
explicitly internal.
.TP
.B \-fall\-virtual
Treat all possible member functions as virtual, implicitly.  All
member functions (except for constructor functions and
.B new
or
.B delete
member operators) are treated as virtual functions of the class where
they appear.
.Sp
This does not mean that all calls to these member functions will be
made through the internal table of virtual functions.  Under some
circumstances, the compiler can determine that a call to a given
virtual function can be made directly; in these cases the calls are
direct in any case.
.TP
.B \-fcond\-mismatch
Allow conditional expressions with mismatched types in the second and
third arguments.  The value of such an expression is void.
.TP
.B \-fthis\-is\-variable
Permit assignment to \c
.B this\c
\& (C++ only).  The incorporation of
user-defined free store management into C++ has made assignment to
`\|\c
.B this\c
\&\|' an anachronism.  Therefore, by default it is invalid to
assign to \c
.B this\c
\& within a class member function.  However, for
backwards compatibility, you can make it valid with
`\|\c
.B \-fthis-is-variable\c
\&\|'.
.TP
.B \-funsigned\-char
Let the type \c
.B char\c
\& be unsigned, like \c
.B unsigned char\c
\&.
.Sp
Each kind of machine has a default for what \c
.B char\c
\& should
be.  It is either like \c
.B unsigned char\c
\& by default or like
.B signed char\c
\& by default.
.Sp
Ideally, a portable program should always use \c
.B signed char\c
\& or
.B unsigned char\c
\& when it depends on the signedness of an object.
But many programs have been written to use plain \c
.B char\c
\& and
expect it to be signed, or expect it to be unsigned, depending on the
machines they were written for.  This option, and its inverse, let you
make such a program work with the opposite default.
.Sp
The type \c
.B char\c
\& is always a distinct type from each of
.B signed char\c
\& and \c
.B unsigned char\c
\&, even though its behavior
is always just like one of those two.
.TP
.B \-fsigned\-char
Let the type \c
.B char\c
\& be signed, like \c
.B signed char\c
\&.
.Sp
Note that this is equivalent to `\|\c
.B \-fno\-unsigned\-char\c
\&\|', which is
the negative form of `\|\c
.B \-funsigned\-char\c
\&\|'.  Likewise,
`\|\c
.B \-fno\-signed\-char\c
\&\|' is equivalent to `\|\c
.B \-funsigned\-char\c
\&\|'.
.TP
.B \-fsigned\-bitfields
.TP
.B \-funsigned\-bitfields
.TP
.B \-fno\-signed\-bitfields
.TP
.B \-fno\-unsigned\-bitfields
These options control whether a bitfield is
signed or unsigned, when declared with no explicit `\|\c
.B signed\c
\&\|' or `\|\c
.B unsigned\c
\&\|' qualifier.  By default, such a bitfield is
signed, because this is consistent: the basic integer types such as
.B int\c
\& are signed types.
.Sp
However, when you specify `\|\c
.B \-traditional\c
\&\|', bitfields are all unsigned
no matter what.
.TP
.B \-fwritable\-strings
Store string constants in the writable data segment and don't uniquize
them.  This is for compatibility with old programs which assume they
can write into string constants.  `\|\c
.B \-traditional\c
\&\|' also has this
effect.
.Sp
Writing into string constants is a very bad idea; \*(lqconstants\*(rq should
be constant.
.SH PREPROCESSOR OPTIONS
These options control the C preprocessor, which is run on each C source
file before actual compilation.
.PP
If you use the `\|\c
.B \-E\c
\&\|' option, GCC does nothing except preprocessing.
Some of these options make sense only together with `\|\c
.B \-E\c
\&\|' because
they cause the preprocessor output to be unsuitable for actual
compilation.
.TP
.BI "\-include " "file"
Process \c
.I file\c
\& as input before processing the regular input file.
In effect, the contents of \c
.I file\c
\& are compiled first.  Any `\|\c
.B \-D\c
\&\|'
and `\|\c
.B \-U\c
\&\|' options on the command line are always processed before
`\|\c
.B \-include \c
.I file\c
\&\c
\&\|', regardless of the order in which they are
written.  All the `\|\c
.B \-include\c
\&\|' and `\|\c
.B \-imacros\c
\&\|' options are
processed in the order in which they are written.
.TP
.BI "\-imacros " file
Process \c
.I file\c
\& as input, discarding the resulting output, before
processing the regular input file.  Because the output generated from
.I file\c
\& is discarded, the only effect of `\|\c
.B \-imacros \c
.I file\c
\&\c