Issues with std::format in CLion 2024.3: Incorrect Template Deduction and Errors Related to const char*， std::string and bf16

已回答

创建于 2024年11月23日 03:11

Hi everyone,

I'm facing an issue with std::format in CLion 2024.3. For the following code:

#include <iostream>
#include <format>
#include <string>
int main() {
   std::cout << std::format("Hello, {}!\n", "World");
   return 0;
}

CLion complains at std::format :

In template: 'auto' in return type deduced as 'type_identity<const std::basic_format_arg<std::basic_format_context<std::__format::_Sink_iter<char>, char>>::_CharT *>' (aka 'type_identity<const char *>') here but deduced as 'type_identity<float>' in earlier return statement 
...

so I jumped there and check why it produced a float. After looking into the code around the error, I noticed the issue seems to be related to a conditional block in the GCC-provided standard library headers format:


#if defined(__BFLT16_DIG__) && defined(_GLIBCXX_FLOAT_IS_IEEE_BINARY32)
   else if constexpr (is_same_v<_Td, decltype(0.0bf16)>)
       return type_identity<float>();
#endif
...
else if constexpr (is_same_v<decay_t<_Td>, const _CharT*>)
   return type_identity<const _CharT*>();
else if constexpr (is_same_v<decay_t<_Td>, _CharT*>)
   return type_identity<const _CharT*>();

It seems like CLion is not handling this properly, as it gives an error at 0.0bf16 saying that Invalid suffix 'bf16' on floating constant . This may be affecting the template deduction process, causing the incorrect deduction of const char* and leading to the error above.

When I manually compile the same code using GCC (version 14.2.1), there are no issues at all, which makes me think this could be a problem with how CLion is handling the standard library or template deduction.

I've also tried replacing const char* with std::string and encountered similar issues, but switching to basic types like int or float works fine.

Has anyone else experienced a similar issue with std::format in CLion? Any advice on how to fix this or work around it?

Thanks in advance for any help!

4 条评论

Anna Falevskaya

创建于 2024年11月28日 16:31

Hello!

Please enable the Nova engine - https://www.jetbrains.com/help/clion/clion-nova-introduction.html. On my side, it doesn't produce the error.

Bart van Hofwegen

创建于 2025年08月05日 15:45

After updating to 20215.2 (Build #CL-252.23892.426, built on August 2, 2025) today (with Nova enabled), I have this exact problem with clangd, also in std::format (via std::println):

std::println("Ocpp_proxy {} {} {}", evse_id_.value(), what, text);

(all 3 arguments are std::string_view) Gives:

Clangd: In template: 'auto' in return type deduced as 'type_identity<basic_string_view<std::basic_format_arg<std::basic_format_context<std::__format::_Sink_iter<char>, char>>::_CharT>>' (aka 'type_identity<basic_string_view<char>>') here but deduced as 'type_identity<float>' in earlier return statement

and

std::println("Ocpp_proxy {} {}", id, what);

Again, (arguments are std::string_view) gives:

Clangd: In template: no matching function for call to '_S_to_arg_type'

All code compiles fine however. I can disable Clangd but that seems suboptimal?

Jon Cppl

创建于 2025年08月22日 19:36

CLion 2025.2
Build #CL-252.23892.426, built on August 2, 2025
Source revision: fe91b356294c0

For my code that otherwise compiles fine, the IDE highlights all calls to std::format as errors

Using a method that indirectly invokes std::format:
Clangd: In template: 'auto' in return type deduced as 'type_identity<double>' here but deduced as 'type_identity<float>' in earlier return statement

public method
static void trace<Args...>(
spdlog::format_string_t<Args...> fmt,
Args&&... args)
in struct DeclaredLogger<NameProvider>

and with std::format directly:
Clangd: In template: no member named '_M_dbl' in 'std::__format::_Arg_value<std::basic_format_context<std::__format::_Sink_iter<char>, char>>'

function
inline string format<_Args...>(
format_string<_Args...> __fmt,
_Args&&... __args)
in namespace std

using Nova Engine and compiler is GCC 13.3.0. Pretty sure I get the same error on MSVC as well.

Anna Falevskaya

创建于 2025年09月08日 12:03

Jon Cppl, it looks like CPP-42195. It should be fixed in the first CLion 2025.3 EAP build, which is tentatively scheduled for release this week.

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