https://gcc.gnu.org/bugzilla/show_bug.cgi?id=122905
Bug ID: 122905
Summary: ODR warning with C++11 and C++20 std::string use
Product: gcc
Version: 16.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: nvinson234 at gmail dot com
Target Milestone: ---
Created attachment 62932
--> https://gcc.gnu.org/bugzilla/attachment.cgi?id=62932&action=edit
example.tar.gz
When linking objects built against mixed C++ standards, g++ issues the
following warning (note: -Werror is also specified, so diagnostic messages say
error):
a.h:6:13: error: ‘example’ violates the C++ One Definition Rule
[-Werror=odr]
6 | std::string example();
| ^
a.cc:3:13: note: return value type mismatch
3 | std::string example()
| ^
a.cc:3:13: note: type ‘struct string’ itself violates the C++ One
Definition Rule
a.cc:3:13: note: ‘example’ was previously declared here
lto1: some warnings being treated as errors
lto-wrapper: fatal error: g++-16 returned 1 exit status
compilation terminated.
/usr/lib/gcc/x86_64-pc-linux-gnu/16/../../../../x86_64-pc-linux-gnu/bin/ld:
error: lto-wrapper failed
collect2: error: ld returned 1 exit status
Steps to reproduce:
1. download example.tar.gz
2. extract archive
3. run driver.sh script
4. observe failure
Additional notes:
g++-16 version: g++-16 (Gentoo 16.0.9999 p, commit
2896409d3014457af03090f2e3bc26e66f2d6381) 16.0.0 20251128 (experimental)
c64308e297a13d0f0e19ec871b5e81348b4da484
When using g++-15 (Gentoo 15.2.1_p20251108-r1 p2) 15.2.1 20251108 the linker
exits successfully.
Warning also appears when linking an object built with c++-17 with one built
with c++-20.
