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-D name
    Predefine name as a macro, with definition 1.
-D name=definition
    The contents of definition are tokenized and processed as if they appeared during translation phase
    three in a #define directive.  In particular, the definition will be truncated by embedded newline

    If you are invoking the preprocessor from a shell or shell-like program you may need to use the
    shell's quoting syntax to protect characters such as spaces that have a meaning in the shell syntax.

    If you wish to define a function-like macro on the command line, write its argument list with
    surrounding parentheses before the equals sign (if any).  Parentheses are meaningful to most shells,
    so you will need to quote the option.  With sh and csh, -D'name(args...)=definition' works.

    -D and -U options are processed in the order they are given on the command line.  All -imacros file
    and -include file options are processed after all -D and -U options.
-U name
    Cancel any previous definition of name, either built in or provided with a -D option.
    Do not predefine any system-specific or GCC-specific macros.  The standard predefined macros remain
-I dir
    Add the directory dir to the list of directories to be searched for header files.

    Directories named by -I are searched before the standard system include directories.  If the
    directory dir is a standard system include directory, the option is ignored to ensure that the
    default search order for system directories and the special treatment of system headers are not
    defeated .  If dir begins with "=", then the "=" will be replaced by the sysroot prefix; see
    --sysroot and -isysroot.
-o file
    Write output to file.  This is the same as specifying file as the second non-option argument to cpp.
    gcc has a different interpretation of a second non-option argument, so you must use -o to specify the
    output file.
    Turns on all optional warnings which are desirable for normal code.  At present this is -Wcomment,
    -Wtrigraphs, -Wmultichar and a warning about integer promotion causing a change of sign in "#if"
    expressions.  Note that many of the preprocessor's warnings are on by default and have no options to
    control them.
    Warn whenever a comment-start sequence /* appears in a /* comment, or whenever a backslash-newline
    appears in a // comment.  (Both forms have the same effect.)
    Most trigraphs in comments cannot affect the meaning of the program.  However, a trigraph that would
    form an escaped newline (??/ at the end of a line) can, by changing where the comment begins or ends.
    Therefore, only trigraphs that would form escaped newlines produce warnings inside a comment.

    This option is implied by -Wall.  If -Wall is not given, this option is still enabled unless
    trigraphs are enabled.  To get trigraph conversion without warnings, but get the other -Wall
    warnings, use -trigraphs -Wall -Wno-trigraphs.
    Warn about certain constructs that behave differently in traditional and ISO C.  Also warn about ISO
    C constructs that have no traditional C equivalent, and problematic constructs which should be
    Warn whenever an identifier which is not a macro is encountered in an #if directive, outside of
    defined.  Such identifiers are replaced with zero.
    Warn about macros defined in the main file that are unused.  A macro is used if it is expanded or
    tested for existence at least once.  The preprocessor will also warn if the macro has not been used
    at the time it is redefined or undefined.

    Built-in macros, macros defined on the command line, and macros defined in include files are not
    warned about.

    Note: If a macro is actually used, but only used in skipped conditional blocks, then CPP will report
    it as unused.  To avoid the warning in such a case, you might improve the scope of the macro's
    definition by, for example, moving it into the first skipped block.  Alternatively, you could provide
    a dummy use with something like:

            #if defined the_macro_causing_the_warning
    Warn whenever an #else or an #endif are followed by text.  This usually happens in code of the form

            #if FOO
            #else FOO
            #endif FOO

    The second and third "FOO" should be in comments, but often are not in older programs.  This warning
    is on by default.
    Make all warnings into hard errors.  Source code which triggers warnings will be rejected.
    Issue warnings for code in system headers.  These are normally unhelpful in finding bugs in your own
    code, therefore suppressed.  If you are responsible for the system library, you may want to see them.
-w  Suppress all warnings, including those which GNU CPP issues by default.
    Issue all the mandatory diagnostics listed in the C standard.  Some of them are left out by default,
    since they trigger frequently on harmless code.
    Issue all the mandatory diagnostics, and make all mandatory diagnostics into errors.  This includes
    mandatory diagnostics that GCC issues without -pedantic but treats as warnings.
-M  Instead of outputting the result of preprocessing, output a rule suitable for make describing the
    dependencies of the main source file.  The preprocessor outputs one make rule containing the object
    file name for that source file, a colon, and the names of all the included files, including those
    coming from -include or -imacros command line options.
-MF file
    When used with -M or -MM, specifies a file to write the dependencies to.  If no -MF switch is given
    the preprocessor sends the rules to the same place it would have sent preprocessed output.
-MT target
    Change the target of the rule emitted by dependency generation.  By default CPP takes the name of the
    main input file, deletes any directory components and any file suffix such as .c, and appends the
    platform's usual object suffix.  The result is the target.

    An -MT option will set the target to be exactly the string you specify.  If you want multiple
    targets, you can specify them as a single argument to -MT, or use multiple -MT options.

    For example, -MT '$(objpfx)foo.o' might give

            $(objpfx)foo.o: foo.c
-MQ target
    Same as -MT, but it quotes any characters which are special to Make.  -MQ '$(objpfx)foo.o' gives
    Like -MD except mention only user header files, not system header files.
-x c
-x c++
-x objective-c
-x assembler-with-cpp
    Specify the source language: C, C++, Objective-C, or assembly.  This has nothing to do with standards
    conformance or extensions; it merely selects which base syntax to expect.  If you give none of these
    options, cpp will deduce the language from the extension of the source file: .c, .cc, .m, or .S.
    Some other common extensions for C++ and assembly are also recognized.  If cpp does not recognize the
    extension, it will treat the file as C; this is the most generic mode.

    Note: Previous versions of cpp accepted a -lang option which selected both the language and the
    standards conformance level.  This option has been removed, because it conflicts with the -l option.
    Specify the standard to which the code should conform.  Currently CPP knows about C and C++
    standards; others may be added in the future.
    Do not search the standard system directories for header files.  Only the directories you have
    specified with -I options (and the directory of the current file, if appropriate) are searched.
-include file
    Process file as if "#include "file"" appeared as the first line of the primary source file.  However,
    the first directory searched for file is the preprocessor's working directory instead of the
    directory containing the main source file.  If not found there, it is searched for in the remainder
    of the "#include "..."" search chain as normal.

    If multiple -include options are given, the files are included in the order they appear on the
    command line.
-imacros file
    Exactly like -include, except that any output produced by scanning file is thrown away.  Macros it
    defines remain defined.  This allows you to acquire all the macros from a header without also
    processing its declarations.

    All files specified by -imacros are processed before all files specified by -include.
-idirafter dir
    Search dir for header files, but do it after all directories specified with -I and the standard
    system directories have been exhausted.  dir is treated as a system include directory.  If dir begins
    with "=", then the "=" will be replaced by the sysroot prefix; see --sysroot and -isysroot.
-iprefix prefix
    Specify prefix as the prefix for subsequent -iwithprefix options.  If the prefix represents a
    directory, you should include the final /.
-iwithprefix dir
-iwithprefixbefore dir
    Append dir to the prefix specified previously with -iprefix, and add the resulting directory to the
    include search path.  -iwithprefixbefore puts it in the same place -I would; -iwithprefix puts it
    where -idirafter would.
-isysroot dir
    This option is like the --sysroot option, but applies only to header files (except for Darwin
    targets, where it applies to both header files and libraries).  See the --sysroot option for more
-imultilib dir
    Use dir as a subdirectory of the directory containing target-specific C++ headers.
-isystem dir
    Search dir for header files, after all directories specified by -I but before the standard system
    directories.  Mark it as a system directory, so that it gets the same special treatment as is applied
    to the standard system directories.

    If dir begins with "=", then the "=" will be replaced by the sysroot prefix; see --sysroot and
-iquote dir
    Search dir only for header files requested with "#include "file""; they are not searched for
    "#include <file>", before all directories specified by -I and before the standard system directories.

    If dir begins with "=", then the "=" will be replaced by the sysroot prefix; see --sysroot and
    When preprocessing, handle directives, but do not expand macros.

    The option's behavior depends on the -E and -fpreprocessed options.

    With -E, preprocessing is limited to the handling of directives such as "#define", "#ifdef", and
    "#error".  Other preprocessor operations, such as macro expansion and trigraph conversion are not
    performed.  In addition, the -dD option is implicitly enabled.

    With -fpreprocessed, predefinition of command line and most builtin macros is disabled.  Macros such
    as "__LINE__", which are contextually dependent, are handled normally.  This enables compilation of
    files previously preprocessed with "-E -fdirectives-only".

    With both -E and -fpreprocessed, the rules for -fpreprocessed take precedence.  This enables full
    preprocessing of files previously preprocessed with "-E -fdirectives-only".
    Accept $ in identifiers.
    Accept universal character names in identifiers.  This option is experimental; in a future version of
    GCC, it will be enabled by default for C99 and C++.
    Indicate to the preprocessor that the input file has already been preprocessed.  This suppresses
    things like macro expansion, trigraph conversion, escaped newline splicing, and processing of most
    directives.  The preprocessor still recognizes and removes comments, so that you can pass a file
    preprocessed with -C to the compiler without problems.  In this mode the integrated preprocessor is
    little more than a tokenizer for the front ends.

    -fpreprocessed is implicit if the input file has one of the extensions .i, .ii or .mi.  These are the
    extensions that GCC uses for preprocessed files created by -save-temps.
    Set the distance between tab stops.  This helps the preprocessor report correct column numbers in
    warnings or errors, even if tabs appear on the line.  If the value is less than 1 or greater than
    100, the option is ignored.  The default is 8.
    Set the execution character set, used for string and character constants.  The default is UTF-8.
    charset can be any encoding supported by the system's "iconv" library routine.
    Set the wide execution character set, used for wide string and character constants.  The default is
    UTF-32 or UTF-16, whichever corresponds to the width of "wchar_t".  As with -fexec-charset, charset
    can be any encoding supported by the system's "iconv" library routine; however, you will have
    problems with encodings that do not fit exactly in "wchar_t".
    Set the input character set, used for translation from the character set of the input file to the
    source character set used by GCC.  If the locale does not specify, or GCC cannot get this information
    from the locale, the default is UTF-8.  This can be overridden by either the locale or this command
    line option.  Currently the command line option takes precedence if there's a conflict.  charset can
    be any encoding supported by the system's "iconv" library routine.
    Enable generation of linemarkers in the preprocessor output that will let the compiler know the
    current working directory at the time of preprocessing.  When this option is enabled, the
    preprocessor will emit, after the initial linemarker, a second linemarker with the current working
    directory followed by two slashes.  GCC will use this directory, when it's present in the
    preprocessed input, as the directory emitted as the current working directory in some debugging
    information formats.  This option is implicitly enabled if debugging information is enabled, but this
    can be inhibited with the negated form -fno-working-directory.  If the -P flag is present in the
    command line, this option has no effect, since no "#line" directives are emitted whatsoever.
    Do not print column numbers in diagnostics.  This may be necessary if diagnostics are being scanned
    by a program that does not understand the column numbers, such as dejagnu.
-A predicate=answer
    Make an assertion with the predicate predicate and answer answer.  This form is preferred to the
    older form -A predicate(answer), which is still supported, because it does not use shell special
-A -predicate=answer
    Cancel an assertion with the predicate predicate and answer answer.
    CHARS is a sequence of one or more of the following characters, and must not be preceded by a space.
    Other characters are interpreted by the compiler proper, or reserved for future versions of GCC, and
    so are silently ignored.  If you specify characters whose behavior conflicts, the result is
-P  Inhibit generation of linemarkers in the output from the preprocessor.  This might be useful when
    running the preprocessor on something that is not C code, and will be sent to a program which might
    be confused by the linemarkers.
-C  Do not discard comments.  All comments are passed through to the output file, except for comments in
    processed directives, which are deleted along with the directive.

    You should be prepared for side effects when using -C; it causes the preprocessor to treat comments
    as tokens in their own right.  For example, comments appearing at the start of what would be a
    directive line have the effect of turning that line into an ordinary source line, since the first
    token on the line is no longer a #.

-CC Do not discard comments, including during macro expansion.  This is like -C, except that comments
    contained within macros are also passed through to the output file where the macro is expanded.

    In addition to the side-effects of the -C option, the -CC option causes all C++-style comments inside
    a macro to be converted to C-style comments.  This is to prevent later use of that macro from
    inadvertently commenting out the remainder of the source line.

    The -CC option is generally used to support lint comments.
    Try to imitate the behavior of old-fashioned C preprocessors, as opposed to ISO C preprocessors.
    Process trigraph sequences.
    Enable special code to work around file systems which only permit very short file names, such as MS-
    Print text describing all the command line options instead of preprocessing anything.
-v  Verbose mode.  Print out GNU CPP's version number at the beginning of execution, and report the final
    form of the include path.
-H  Print the name of each header file used, in addition to other normal activities.  Each name is
    indented to show how deep in the #include stack it is.  Precompiled header files are also printed,
    even if they are found to be invalid; an invalid precompiled header file is printed with ...x and a
    valid one with ...! .
    Print out GNU CPP's version number.  With one dash, proceed to preprocess as normal.  With two
    dashes, exit immediately.

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