https://gcc.gnu.org/bugzilla/show_bug.cgi?id=101957
Bug ID: 101957
Summary: Multiple definition of static constexpr data member
when C++11 and C++17 objects are mixed
Product: gcc
Version: 9.3.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: wpty9420 at gmail dot com
Target Milestone: ---
I requested help about this problem in the gcc-help mailing list and I was
asked to report it as a bug. My e-mail and its thread are here:
https://gcc.gnu.org/pipermail/gcc-help/2021-August/140618.html
I have a very small reproducer:
$ cat lib.h
#pragma once
struct A {
static constexpr int x{ -1 };
};
void f(const int &x);
$ cat lib.cpp
#include "lib.h"
constexpr int A::x;
void f(const int& x) {}
$ cat main.cpp
#include "lib.h"
int main() {
f(A::x);
return 0;
}
$ g++ -std=c++11 -o lib.o -c lib.cpp
$ g++ -std=c++17 -o main.o -c main.cpp
$ g++ -o main lib.o main.o
/usr/bin/ld: main.o:(.rodata._ZN1A1xE[_ZN1A1xE]+0x0): multiple definition of
`A::x'; lib.o:(.rodata+0x0): first defined here
collect2: error: ld returned 1 exit status
C++11 standard requires the definition of static constexpr data members if they
are odr-used and C++17 allows it even though it's redundant. So, I think this
should compile without errors.
I get the same error with GCC 9.3.0 and 11.0.1, the output of g++ -v for both
versions are as follows:
$ g++ -v
Using built-in specs.
COLLECT_GCC=g++
COLLECT_LTO_WRAPPER=/usr/lib/gcc/x86_64-linux-gnu/9/lto-wrapper
OFFLOAD_TARGET_NAMES=nvptx-none:hsa
OFFLOAD_TARGET_DEFAULT=1
Target: x86_64-linux-gnu
Configured with: ../src/configure -v --with-pkgversion='Ubuntu
9.3.0-17ubuntu1~20.04' --with-bugurl=file:///usr/share/doc/gcc-9/README.Bugs
--enable-languages=c,ada,c++,go,brig,d,fortran,objc,obj-c++,gm2 --prefix=/usr
--with-gcc-major-version-only --program-suffix=-9
--program-prefix=x86_64-linux-gnu- --enable-shared --enable-linker-build-id
--libexecdir=/usr/lib --without-included-gettext --enable-threads=posix
--libdir=/usr/lib --enable-nls --enable-clocale=gnu --enable-libstdcxx-debug
--enable-libstdcxx-time=yes --with-default-libstdcxx-abi=new
--enable-gnu-unique-object --disable-vtable-verify --enable-plugin
--enable-default-pie --with-system-zlib --with-target-system-zlib=auto
--enable-objc-gc=auto --enable-multiarch --disable-werror --with-arch-32=i686
--with-abi=m64 --with-multilib-list=m32,m64,mx32 --enable-multilib
--with-tune=generic
--enable-offload-targets=nvptx-none=/build/gcc-9-HskZEa/gcc-9-9.3.0/debian/tmp-nvptx/usr,hsa
--without-cuda-driver --enable-checking=release --build=x86_64-linux-gnu
--host=x86_64-linux-gnu --target=x86_64-linux-gnu
Thread model: posix
gcc version 9.3.0 (Ubuntu 9.3.0-17ubuntu1~20.04)
$ g++-11 -v
Using built-in specs.
COLLECT_GCC=g++-11
COLLECT_LTO_WRAPPER=/usr/lib/gcc/x86_64-linux-gnu/11/lto-wrapper
OFFLOAD_TARGET_NAMES=nvptx-none:amdgcn-amdhsa
Target: x86_64-linux-gnu
Configured with: ../src/configure -v --with-pkgversion='Ubuntu
11-20210417-1ubuntu1' --with-bugurl=file:///usr/share/doc/gcc-11/README.Bugs
--enable-languages=c,ada,c++,go,brig,d,fortran,objc,obj-c++,m2 --prefix=/usr
--with-gcc-major-version-only --program-suffix=-11
--program-prefix=x86_64-linux-gnu- --enable-shared --enable-linker-build-id
--libexecdir=/usr/lib --without-included-gettext --enable-threads=posix
--libdir=/usr/lib --enable-nls --enable-bootstrap --enable-clocale=gnu
--enable-libstdcxx-debug --enable-libstdcxx-time=yes
--with-default-libstdcxx-abi=new --enable-gnu-unique-object
--disable-vtable-verify --enable-plugin --enable-default-pie --with-system-zlib
--enable-libphobos-checking=release --with-target-system-zlib=auto
--enable-objc-gc=auto --enable-multiarch --disable-werror --enable-cet
--with-arch-32=i686 --with-abi=m64 --with-multilib-list=m32,m64,mx32
--enable-multilib --with-tune=generic
--enable-offload-targets=nvptx-none=/build/gcc-11-pzZXCn/gcc-11-11-20210417/debian/tmp-nvptx/usr,amdgcn-amdhsa=/build/gcc-11-pzZXCn/gcc-11-11-20210417/debian/tmp-gcn/usr
--without-cuda-driver --enable-checking=release --build=x86_64-linux-gnu
--host=x86_64-linux-gnu --target=x86_64-linux-gnu
--with-build-config=bootstrap-lto-lean --enable-link-serialization=2
Thread model: posix
Supported LTO compression algorithms: zlib zstd
gcc version 11.0.1 20210417 (experimental) [master revision
c1c86ab96c2:b6fb0ccbb48:8ae884c09fbba91e9cec391290ee4a2859e7ff41] (Ubuntu
11-20210417-1ubuntu1)
