Compile Error VS2019

[urusaiurusai]

• Error C2993 'fmt::v5::internal::value': illegal type for non-type template parameter '_Test' F:\project\fmt\include\fmt\core.h 904

• Error C2039 'type': is not a member of 'std' F:\project\fmt\include\fmt\core.h 903

I just #include <fmt/format.h> and do nothing. everything works fine when building the source.

[vitaut]

The error looks weird because there is no template parameter _Test anywhere in the library. Perhaps you are seeing some macro conflict from elsewhere.

[vitaut]

Also I couldn't repro this on godbolt: https://godbolt.org/z/jHsYkN

[urusaiurusai]

The errors disapeared if directly append these source code format.h, core.h, format-inl.h and format.cc to a helloworld project instead of using the compiled library fmtd.lib and #include <fmt/format.h>.

There must be something wrong but i can't figure it out. Anyway, I am happy to see it works now.

Thanks.

[mocabe]

I experienced same issue with msvc19.21 (VS2019 16.1.0 Preview 3.0).
#include <fmt/format.h> causes this problem.
It seems that MSVC cannot parse (or process) following line correctly.

template <typename C, typename S, FMT_ENABLE_IF(internal::is_string<S>::value)>

Template parameter _Test is probably a parameters of std::enable_if in microsoft STL.

// STRUCT TEMPLATE enable_if
template <bool _Test, class _Ty = void>
struct enable_if {}; // no member "type" when !_Test

The problem is typename internal::is_string<S>::value being processed into fmt::v5::internal::value for some reason. poor is_string<S> 😿

Adding additional parentheses around condition parameter fixed the problem for me.
i.e. change

#define FMT_ENABLE_IF(...) typename std::enable_if<__VA_ARGS__, int>::type = 0

to

#define FMT_ENABLE_IF(...) typename std::enable_if<(__VA_ARGS__), int>::type = 0