https://gcc.gnu.org/bugzilla/show_bug.cgi?id=127081
Bug ID: 127081
Summary: Within std::format, constexpr expansion of
std::basic_format_string errors with: strong_ordering
is not a member of 'std'
Product: gcc
Version: 16.2.1
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: sebj_coder3 at pm dot me
Target Milestone: ---
I'm getting an error when compiling a C++ module which makes use of
std::format. I think the code should compile, because clang-20 and up do so
without error.
The error output is:
-------------------------------
/opt/gcc16/bin/g++ -I/home/seb/src/mathplot -I/home/seb/src/mathplot/maths
-I/home/seb/src/mathplot/json/include -isystem /usr/include/freetype2
-static-libstdc++ -g -Wall -Wextra -Wpedantic -pedantic-errors -Werror
-Wfatal-errors -Wno-psabi -Wno-unknown-pragmas -O3
-fconstexpr-ops-limit=5000000000
-DMPLOT_FONTS_DIR="\"/home/seb/src/mathplot/fonts\"" -freport-bug -std=gnu++20
-MD -MT examples/CMakeFiles/helloworld.dir/helloworld.cpp.o -MF
examples/CMakeFiles/helloworld.dir/helloworld.cpp.o.d -fmodules-ts
-fmodule-mapper=examples/CMakeFiles/helloworld.dir/helloworld.cpp.o.modmap -MD
-fdeps-format=p1689r5 -x c++ -o
examples/CMakeFiles/helloworld.dir/helloworld.cpp.o -c
/home/seb/src/mathplot/examples/helloworld.cpp
In file included from /home/seb/src/mathplot/maths/sm/mat.cppm:27,
of module sm.mat, imported at
/home/seb/src/mathplot/mplot/VisualCommon.cppm:20,
of module mplot.visualcommon, imported at
/home/seb/src/mathplot/mplot/VisualResources.cppm:30,
of module mplot.visualresources, imported at
/home/seb/src/mathplot/mplot/Visual.cppm:35,
of module mplot.visual, imported at
/home/seb/src/mathplot/examples/helloworld.cpp:1:
/opt/gcc16/include/c++/16.2.1/format: In instantiation of 'constexpr void
std::__format::_Scanner<_CharT>::_M_scan() [with _CharT = char]':
/opt/gcc16/include/c++/16.2.1/format:5392:19: required from 'static
std::string sm::[email protected]<F, Nr, Nc>::str_arr(const sm::[email protected]<F, (Nr *
Nc)>&, uint32_t) [with F = float; unsigned int Nr = 4; unsigned int Nc = 4;
std::string = std::__cxx11::basic_string<char>; uint32_t = unsigned int]'
5392 | __scanner._M_scan();
| ~~~~~~~~~~~~~~~~~^~
/home/seb/src/mathplot/maths/sm/mat.cppm:200:28: required from 'std::string
sm::[email protected]<F, Nr, Nc>::str_arr(uint32_t) const [with F = float; unsigned
int Nr = 4; unsigned int Nc = 4; std::string =
std::__cxx11::basic_string<char>; uint32_t = unsigned int]'
200 | return str_arr (this->arr, prec);
| ~~~~~~~~^~~~~~~~~~~~~~~~~
/home/seb/src/mathplot/mplot/VisualOwnable.cppm:1906:86: required from 'bool
mplot::[email protected]<glver>::key_callback(int32_t, int32_t,
int32_t, int32_t) [with bool owned = true; int glver = 262145; int32_t = int]'
1906 | std::cout << " Sceneview matrix array:\n" <<
this->sceneview.str_arr() << std::endl;
|
~~~~~~~~~~~~~~~~~~~~~~~^~
/home/seb/src/mathplot/mplot/Visual.cppm:305:77: required from 'bool
mplot::[email protected]<glver>::key_callback(int32_t, int32_t, int32_t,
int32_t) [with int glver = 262145; int32_t = int]'
305 | return mplot::VisualOwnable<glver>::template
key_callback<true> (_key, scancode, action, mods);
|
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/home/seb/src/mathplot/mplot/Visual.cppm:254:23: required from 'static void
mplot::[email protected]<glver>::key_callback_dispatch(GLFWwindow*, int32_t,
int32_t, int32_t, int32_t) [with int glver = 262145; GLFWwindow = GLFWwindow;
int32_t = int]'
254 | if (self->key_callback (key, scancode, action, mods)) {
| ~~~~~~^~~~~~~~~~~~
/home/seb/src/mathplot/mplot/Visual.cppm:230:32: required from 'void
mplot::[email protected]<glver>::init_window() [with int glver = 262145]'
230 | glfwSetKeyCallback (this->window, key_callback_dispatch);
| ~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/home/seb/src/mathplot/mplot/Visual.cppm:99:19: required from 'void
mplot::[email protected]<glver>::init_resources() [with int glver = 262145]'
99 | this->init_window();
| ~~~~~~^~~~~~~~~~~
/home/seb/src/mathplot/mplot/Visual.cppm:73:19: required from
'mplot::[email protected]<glver>::Visual(int32_t, int32_t, const
std::string&, bool) [with int glver = 262145; int32_t = int; std::string =
std::__cxx11::basic_string<char>]'
73 | this->init_resources();
| ~~~~~~^~~~~~~~~~~~~~
/home/seb/src/mathplot/examples/helloworld.cpp:6:69: required from here
6 | mplot::Visual<mplot::gl::version_4_1> v(600, 400, "Hello World!");
| ^
/home/seb/src/mathplot/maths/sm/mat.cppm:187:38: in 'constexpr' expansion of
'std::basic_format_string<char, const float&, const unsigned int&>("{:.{}}, ")'
187 | s += std::format ("{:.{}}, ", _arr[i], prec);
| ^~~~~~~~~~
/opt/gcc16/include/c++/16.2.1/format:5016:32: error: 'strong_ordering' is not a
member of 'std'
5016 | auto __cmp = __lbr <=> __rbr;
| ~~~~~~^~~~~~~~~
compilation terminated due to -Wfatal-errors.
-------------------------------
mat.cppm comes from https://github.com/sebsjames/maths. The build that
generates the error is https://github.com/sebsjames/mathplot.
sm::mat is exported from a module sm.mat. The offending call to mat::str_arr()
is found in mplot::VisualOwnable, which is exported from module
mplot.visualownable, and is the base class for mplot::Visual, exported from
mplot.visual.
I have not yet been able to make a reduced example (first attempt compiled
find; I always find this difficult!).
To reproduce the error:
Install some prerequisites for this OpenGL program. On Ubuntu/Debian it's
these:
sudo apt install build-essential cmake git ninja-build \
librapidxml-dev freeglut3-dev libglu1-mesa-dev libxmu-dev \
libxi-dev libglfw3-dev libfreetype-dev libhdf5-dev
PLUS g++ compiled from master or release-16 and cmake at least version 3.28.5.
clone mathplot recursively (it has two submodules):
git clone --recurse-submodules [email protected]:sebsjames/mathplot
switch to the bugs/std_format_no_strong_ordering_in_std branch:
cd mathplot
git checkout bugs/std_format_no_strong_ordering_in_std
git submodule update
Build the 'helloworld' target using cmake:
mkdir bgcc
cd bgcc
CC=/path/to/gcc CXX=/path/to/g++ cmake .. -GNinja
-DCMAKE_CXX_FLAGS="-static-libstdc++"
ninja helloworld
