在 2019/1/14 上午6:46, Maarten Verhage 写道:
> Hi all,
>
> I might have found a bug in gcc or mingw, but I'm not really sure.
>
Generally: This program contains no mingw-w64-specific thing, so it is
less likely to be a mingw-w64 issue. You should have sent this to the
gcc-help mailing list which is more appropriate.
> For the following version:
> g++ (x86_64-win32-seh-rev0, Built by MinGW-W64 project) 8.1.0
>
> A short example:
>
> #include <cstddef>
> #include <cstdio>
> #include <cstdint>
> #include <array>
>
> int main()
> {
> const char istr[] = "Hello";
> std::array<char16_t, std::char_traits<char>::length( istr )> str16;
>
> return 0;
> }
>
> Now the compile step:
>
> g++ -c -std=c++17 -pedantic -Wextra -Wlogical-op test.cpp
> In file included from
> C:/dev/x86_64-8.1.0-release-win32-seh-rt_v6-rev0/mingw64/lib/gcc/x86_64-w64-mingw32/8.1.0/include/c++/string:40,
> from
> C:/dev/x86_64-8.1.0-release-win32-seh-rt_v6-rev0/mingw64/lib/gcc/x86_64-w64-mingw32/8.1.0/include/c++/stdexcept:39,
> from
> C:/dev/x86_64-8.1.0-release-win32-seh-rt_v6-rev0/mingw64/lib/gcc/x86_64-w64-mingw32/8.1.0/include/c++/array:39,
> from test.cpp:4:
> C:/dev/x86_64-8.1.0-release-win32-seh-rt_v6-rev0/mingw64/lib/gcc/x86_64-w64-mingw32/8.1.0/include/c++/bits/char_traits.h:
>
> In function 'int main()':
> test.cpp:9:54: in 'constexpr' expansion of
> 'std::char_traits<char>::length(((const char*)(& istr)))'
> C:/dev/x86_64-8.1.0-release-win32-seh-rt_v6-rev0/mingw64/lib/gcc/x86_64-w64-mingw32/8.1.0/include/c++/bits/char_traits.h:320:25:
>
> error: '__builtin_strlen(((const char_type*)(& istr)))' is not a constant
> expression
> return __builtin_strlen(__s);
> ~~~~~~~~~~~~~~~~^~~~~
> test.cpp:9:54: note: in template argument for type 'long long unsigned int'
> std::array<char16_t, std::char_traits<char>::length( istr )> str16;
> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^~~~~~~~
> mingw32-make.exe: *** [C:\dev\mydesign\SW\C++\win32\array_test\test.mak:9:
> test.o] Error 1
>
> This shouldn't be, right? As it succesfully selects the constexpr function
> variant for the second template argument it should also work further down, I
> believe.
>
Your code is not valid. Clang++ rejects your snippet, too.
The array-to-pointer conversion from an array of `const char` is not
allowed in a constant expression unless such an array is declared with
`constexpr` [1]. Use `constexpr` in place of `const` will solve your
problem.
[1] ISO/IEC WG21 N4762: 7.7 Constant expressions [expr.const], (2.7),
(2.7.1), (2.7.3). <http://eel.is/c++draft/expr.const#4.7>
--
Best regards,
LH_Mouse
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