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From: "Hirthammer@allterra-dno.de" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug libstdc++/113500] New: Using std::format with float or double
 based std::chrono::time_point causes error: no match for 'operator<<'
Date: Fri, 19 Jan 2024 07:11:04 +0000
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X-Bugzilla-Product: gcc
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D113500

            Bug ID: 113500
           Summary: Using std::format with float or double based
                    std::chrono::time_point causes error: no match for
                    'operator<<'
           Product: gcc
           Version: 13.1.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: libstdc++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: Hirthammer@allterra-dno.de
  Target Milestone: ---

Consider the following code snippet:

---
using Representation =3D double;
using Duration       =3D std::chrono::duration<Representation>;
using Clock          =3D std::chrono::system_clock;
using TimePoint      =3D std::chrono::time_point<Clock, Duration>;

TimePoint tp =3D {};

std::string time_string =3D std::format("{:%d.%m.%Y %H:%M:%S}", tp);
---


This results in the compile error:


---
error: no match for 'operator<<' (operand types are
'std::__cxx11::basic_ostringstream<char>' and 'const
std::chrono::time_point<std::chrono::_V2::system_clock,
std::chrono::duration<float> >')
  726 |                   __os << __t;
      |                   ~~~~~^~~~~~
---

If you change the type def `Representation` to an integer or unsigned integ=
er
type, the code compiles.

System Info:

~~~
OS: Ubuntu 22.04 LTS
GCC-Version: 13.1.0
arguments: -std=3Dc++20
~~~

Here is a link with the code that produces the error in Compiler Explorer:

https://godbolt.org/z/hhPrG1z37

Side note:=20
Don't know if it helps, but the latest clang compiler version produces the =
same
error. The related bug report can be found here:

https://github.com/llvm/llvm-project/issues/78555=