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83 lines
2.9 KiB
Plaintext
83 lines
2.9 KiB
Plaintext
@c Copyright (C) 1999-2022 Free Software Foundation, Inc.
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@c This is part of the CPP and GCC manuals.
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@c For copying conditions, see the file gcc.texi.
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@c ---------------------------------------------------------------------
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@c Options affecting preprocessor warnings
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@c ---------------------------------------------------------------------
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@c If this file is included with the flag ``cppmanual'' set, it is
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@c formatted for inclusion in the CPP manual; otherwise the main GCC manual.
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@item -Wcomment
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@itemx -Wcomments
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@opindex Wcomment
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@opindex Wcomments
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Warn whenever a comment-start sequence @samp{/*} appears in a @samp{/*}
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comment, or whenever a backslash-newline appears in a @samp{//} comment.
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This warning is enabled by @option{-Wall}.
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@item -Wtrigraphs
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@opindex Wtrigraphs
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@anchor{Wtrigraphs}
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Warn if any trigraphs are encountered that might change the meaning of
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the program. Trigraphs within comments are not warned about,
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except those that would form escaped newlines.
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This option is implied by @option{-Wall}. If @option{-Wall} is not
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given, this option is still enabled unless trigraphs are enabled. To
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get trigraph conversion without warnings, but get the other
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@option{-Wall} warnings, use @samp{-trigraphs -Wall -Wno-trigraphs}.
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@item -Wundef
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@opindex Wundef
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@opindex Wno-undef
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Warn if an undefined identifier is evaluated in an @code{#if} directive.
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Such identifiers are replaced with zero.
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@item -Wexpansion-to-defined
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@opindex Wexpansion-to-defined
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Warn whenever @samp{defined} is encountered in the expansion of a macro
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(including the case where the macro is expanded by an @samp{#if} directive).
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Such usage is not portable.
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This warning is also enabled by @option{-Wpedantic} and @option{-Wextra}.
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@item -Wunused-macros
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@opindex Wunused-macros
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Warn about macros defined in the main file that are unused. A macro
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is @dfn{used} if it is expanded or tested for existence at least once.
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The preprocessor also warns if the macro has not been used at the
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time it is redefined or undefined.
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Built-in macros, macros defined on the command line, and macros
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defined in include files are not warned about.
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@emph{Note:} If a macro is actually used, but only used in skipped
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conditional blocks, then the preprocessor reports it as unused. To avoid the
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warning in such a case, you might improve the scope of the macro's
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definition by, for example, moving it into the first skipped block.
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Alternatively, you could provide a dummy use with something like:
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@smallexample
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#if defined the_macro_causing_the_warning
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#endif
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@end smallexample
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@item -Wno-endif-labels
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@opindex Wno-endif-labels
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@opindex Wendif-labels
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Do not warn whenever an @code{#else} or an @code{#endif} are followed by text.
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This sometimes happens in older programs with code of the form
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@smallexample
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#if FOO
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@dots{}
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#else FOO
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@dots{}
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#endif FOO
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@end smallexample
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@noindent
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The second and third @code{FOO} should be in comments.
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This warning is on by default.
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