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From: "koncek.marian at gmail dot com" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug c++/101800] New: mingw-64 link error with constexpr static
 variable definition
Date: Fri, 06 Aug 2021 09:55:05 +0000
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D101800

            Bug ID: 101800
           Summary: mingw-64 link error with constexpr static variable
                    definition
           Product: gcc
           Version: 10.3.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: koncek.marian at gmail dot com
  Target Milestone: ---

Version:
x86_64-w64-mingw32-g++ (GCC) 10.3.1 20210422 (Fedora MinGW 10.3.1-1.fc34)

Using 3 source files:
////////////////////////////////////
<test.hpp>

#pragma once

struct S
{
        const static int value;
};
////////////////////////////////////
<test.cpp>

#include "test.hpp"

constexpr int S::value =3D 0;
////////////////////////////////////
<main.cpp>

#include "test.hpp"

int main()
{
        return S::value;
}
////////////////////////////////////

Compile with:
$ x86_64-w64-mingw32-g++ -std=3Dc++2a -c test.cpp && x86_64-w64-mingw32-g++
-std=3Dc++2a test.o main.cpp

Results in:
/usr/lib/gcc/x86_64-w64-mingw32/10.3.1/../../../../x86_64-w64-mingw32/bin/l=
d:
/tmp/ccANpWMi.o:main.cpp:(.rdata$.refptr._ZN1S5valueE[.refptr._ZN1S5valueE]=
+0x0):
undefined reference to `S::value'
collect2: error: ld returned 1 exit status

Whereas plain g++ is able to link the files in the executable.

Changing the `constexpr` definition to `const` makes mingw link the files
successfully.=