[英]why is “cc1plus: warning: unrecognized command line option” for “no-” options only flagged by g++ when there is another warning?
> cat warning.cpp
#pragma foobar
> cat no_warning.cpp
#pragma message "foobar"
> g++ -Wall -Wno-foobar -c warning.cpp
warning.cpp:1:0: warning: ignoring #pragma foobar [-Wunknown-pragmas]
cc1plus: warning: unrecognized command line option "-Wno-foobar" [enabled by default]
> g++ -Wall -Wno-foobar -c no_warning.cpp
no_warning.cpp:1:17: note: #pragma message: foobar
This is by design, explained here : 这是设计, 在这里解释:
When an unrecognized warning option is requested (e.g., -Wunknown-warning),
GCC emits a diagnostic stating that the option is not recognized.
However, if the -Wno- form is used, the behavior is slightly different:
no diagnostic is produced for -Wno-unknown-warning unless other diagnostics
are being produced.
This allows the use of new -Wno- options with old compilers, but if something
goes wrong, the compiler warns that an unrecognized option is present.
In other words, suppose you have foo.cc
, and GCC-4.9 warns about something (let's call it foobar
) in it, but you believe that your use of foobar
is safe. 换句话说,假设你有
foo.cc
,并且GCC-4.9警告某些东西(让我们称之为foobar
),但你相信你使用foobar
是安全的。
Since you want to treat all warnings as errors (with -Werror
), you dutifully add -Wno-foobar
to your Makefile
. 由于您希望将所有警告视为错误(使用
-Werror
),因此请尽职地将-Wno-foobar
添加到Makefile
。
Now someone else tries to build your code with GCC-4.8. 现在有人试图用GCC-4.8构建你的代码。 As stated above, this produces no warning and he succeeds.
如上所述,这不会产生任何警告,他会成功。
If this did produce a warning, you'd be unable to both use the foobar
construct and have a single Makefile
that worked with both GCC-4.8 and GCC-4.9. 如果这确实产生了警告,那么你将无法同时使用
foobar
构造并拥有一个可与GCC-4.8和GCC-4.9一起使用的Makefile
。
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