diff options
Diffstat (limited to 'contrib/gcc/doc/cppopts.texi')
| -rw-r--r-- | contrib/gcc/doc/cppopts.texi | 114 |
1 files changed, 79 insertions, 35 deletions
diff --git a/contrib/gcc/doc/cppopts.texi b/contrib/gcc/doc/cppopts.texi index 308e989..7abb803 100644 --- a/contrib/gcc/doc/cppopts.texi +++ b/contrib/gcc/doc/cppopts.texi @@ -51,16 +51,14 @@ for header files. @xref{Search Path}. @end ifset Directories named by @option{-I} are searched before the standard -system include directories. - -It is dangerous to specify a standard system include directory in an -@option{-I} option. This defeats the special treatment of system -headers +system include directories. If the directory @var{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 @ifset cppmanual (@pxref{System Headers}) @end ifset -. It can also defeat the repairs to buggy system headers which GCC -makes when it is installed. +. @item -o @var{file} @opindex o @@ -110,6 +108,44 @@ Warn whenever an identifier which is not a macro is encountered in an @samp{#if} directive, outside of @samp{defined}. Such identifiers are replaced with zero. +@item -Wunused-macros +@opindex Wunused-macros +Warn about macros defined in the main file that are unused. A macro +is @dfn{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. + +@strong{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: + +@smallexample +#if defined the_macro_causing_the_warning +#endif +@end smallexample + +@item -Wendif-labels +@opindex Wendif-labels +Warn whenever an @samp{#else} or an @samp{#endif} are followed by text. +This usually happens in code of the form + +@smallexample +#if FOO +@dots{} +#else FOO +@dots{} +#endif FOO +@end smallexample + +@noindent +The second and third @code{FOO} should be in comments, but often are not +in older programs. This warning is on by default. + @item -Werror @opindex Werror Make all warnings into hard errors. Source code which triggers warnings @@ -158,10 +194,11 @@ This option does not suppress the preprocessor's debug output, such as @option{-dM}. To avoid mixing such debug output with the dependency rules you should explicitly specify the dependency output file with @option{-MF}, or use an environment variable like -@env{DEPENDENCIES_OUTPUT} (@pxref{DEPENDENCIES_OUTPUT}). Debug output +@env{DEPENDENCIES_OUTPUT} (@pxref{Environment Variables}). Debug output will still be sent to the regular output stream as normal. -Passing @option{-M} to the driver implies @option{-E}. +Passing @option{-M} to the driver implies @option{-E}, and suppresses +warnings with an implicit @option{-w}. @item -MM @opindex MM @@ -187,10 +224,13 @@ When used with the driver options @option{-MD} or @option{-MMD}, @item -MG @opindex MG -When used with @option{-M} or @option{-MM}, @option{-MG} says to treat missing -header files as generated files and assume they live in the same -directory as the source file. It suppresses preprocessed output, as a -missing header file is ordinarily an error. +In conjunction with an option such as @option{-M} requesting +dependency generation, @option{-MG} assumes missing header files are +generated files and adds them to the dependency list without raising +an error. The dependency filename is taken directly from the +@code{#include} directive without prepending any path. @option{-MG} +also suppresses preprocessed output, as a missing header file renders +this useless. This feature is used in automatic updating of makefiles. @@ -284,9 +324,8 @@ option. @itemx -ansi @opindex ansi @opindex std= -Specify the standard to which the code should conform. Currently cpp -only knows about the standards for C; other language standards will be -added in the future. +Specify the standard to which the code should conform. Currently CPP +knows about C and C++ standards; others may be added in the future. @var{standard} may be one of: @@ -314,6 +353,13 @@ The 1990 C standard plus GNU extensions. This is the default. @item gnu99 @itemx gnu9x The 1999 C standard plus GNU extensions. + +@item c++98 +The 1998 ISO C++ standard plus amendments. + +@item gnu++98 +The same as @option{-std=c++98} plus GNU extensions. This is the +default for C++ code. @end table @item -I- @@ -441,13 +487,6 @@ it does not use shell special characters. Cancel an assertion with the predicate @var{predicate} and answer @var{answer}. -@item -A- -@opindex A- -Cancel all predefined assertions and all assertions preceding it on -the command line. Also, undefine all predefined macros and all -macros preceding it on the command line. (This is a historical wart and -may change in the future.) - @item -dCHARS @var{CHARS} is a sequence of one or more of the following characters, and must not be preceded by a space. Other characters are interpreted @@ -510,6 +549,19 @@ 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 @samp{#}. +@item -CC +Do not discard comments, including during macro expansion. This is +like @option{-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 @option{-C} option, the +@option{-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 @option{-CC} option is generally used to support lint comments. + @item -gcc @opindex gcc Define the macros @sc{__gnuc__}, @sc{__gnuc_minor__} and @@ -517,10 +569,10 @@ Define the macros @sc{__gnuc__}, @sc{__gnuc_minor__} and @command{gcc -E}; you can turn them off in that case with @option{-no-gcc}. -@item -traditional -@opindex traditional -Try to imitate the behavior of old-fashioned C, as opposed to ISO -C@. +@item -traditional-cpp +@opindex traditional-cpp +Try to imitate the behavior of old-fashioned C preprocessors, as +opposed to ISO C preprocessors. @ifset cppmanual @xref{Traditional Mode}. @end ifset @@ -552,16 +604,8 @@ Replacement: [ ] @{ @} # \ ^ | ~ Enable special code to work around file systems which only permit very short file names, such as MS-DOS@. -@item -$ -@opindex $ -Forbid the use of @samp{$} in identifiers. The C standard allows -implementations to define extra characters that can appear in -identifiers. By default GNU CPP permits @samp{$}, a common extension. - -@item -h @itemx --help @itemx --target-help -@opindex h @opindex help @opindex target-help Print text describing all the command line options instead of |
