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/usr/include/python3.15/pyport.h:494:9: error: ‘__STDC_VERSION__’ is not defined, evaluates to ‘0’ [-Werror=undef] #154643

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/usr/include/python3.15/pyport.h:494:9: error: ‘__STDC_VERSION__’ is not defined, evaluates to ‘0’ [-Werror=undef]#154643
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buildThe build process and cross-buildtype-bugAn unexpected behavior, bug, or error

Description

@hroncok
hroncok
opened on Jul 24, 2026

Bug report

Bug description:

Hello. When building the kmymoney Fedora package, we got:

In file included from /usr/include/python3.15/Python.h:68,
                 from /builddir/build/BUILD/kmymoney-5.2.2-build/kmymoney-5.2.2/kmymoney/plugins/woob/interface/woobinterface.cpp:16:
/usr/include/python3.15/pyport.h:494:9: error: ‘__STDC_VERSION__’ is not defined, evaluates to ‘0’ [-Werror=undef]
  494 | #  elif __STDC_VERSION__ >= 201112L && !defined(__STDC_NO_THREADS__)
      |         ^~~~~~~~~~~~~~~~

The package uses g++, not gcc.

It has:

#include <Python.h>

The compiler invocation is:

cd /builddir/build/BUILD/kmymoney-5.2.2-build/kmymoney-5.2.2/redhat-linux-build/kmymoney/misc && /usr/bin/g++ -DKF_DEPRECATED_WARNINGS_SINCE=0x60000 -DKF_DISABLE_DEPRECATED_BEFORE_AND_AT=0x56200C -DQT_CORE_LIB -DQT_DEPRECATED_WARNINGS_SINCE=0x60000 -DQT_DISABLE_DEPRECATED_BEFORE=0x50f02 -DQT_NO_CAST_FROM_ASCII -DQT_NO_CAST_FROM_BYTEARRAY -DQT_NO_CAST_TO_ASCII -DQT_NO_DEBUG -DQT_NO_FOREACH -DQT_NO_KEYWORDS -DQT_NO_NARROWING_CONVERSIONS_IN_CONNECT -DQT_NO_URL_CAST_FROM_STRING -DQT_STRICT_ITERATORS -DQT_USE_QSTRINGBUILDER -D_GNU_SOURCE -D_LARGEFILE64_SOURCE -Dkmm_gpgfile_EXPORTS -I/builddir/build/BUILD/kmymoney-5.2.2-build/kmymoney-5.2.2/redhat-linux-build/kmymoney/misc -I/builddir/build/BUILD/kmymoney-5.2.2-build/kmymoney-5.2.2/kmymoney/misc -I/builddir/build/BUILD/kmymoney-5.2.2-build/kmymoney-5.2.2/redhat-linux-build/kmymoney/misc/kmm_gpgfile_autogen/include -I/builddir/build/BUILD/kmymoney-5.2.2-build/kmymoney-5.2.2 -I/builddir/build/BUILD/kmymoney-5.2.2-build/kmymoney-5.2.2/redhat-linux-build -I/builddir/build/BUILD/kmymoney-5.2.2-build/kmymoney-5.2.2/kmymoney -I/builddir/build/BUILD/kmymoney-5.2.2-build/kmymoney-5.2.2/redhat-linux-build/kmymoney -I/builddir/build/BUILD/kmymoney-5.2.2-build/kmymoney-5.2.2/kmymoney/settings -I/builddir/build/BUILD/kmymoney-5.2.2-build/kmymoney-5.2.2/redhat-linux-build/kmymoney/settings -I/builddir/build/BUILD/kmymoney-5.2.2-build/kmymoney-5.2.2/redhat-linux-build/kmymoney/dialogs -I/builddir/build/BUILD/kmymoney-5.2.2-build/kmymoney-5.2.2/kmymoney/widgets -I/builddir/build/BUILD/kmymoney-5.2.2-build/kmymoney-5.2.2/redhat-linux-build/kmymoney/widgets -I/builddir/build/BUILD/kmymoney-5.2.2-build/kmymoney-5.2.2/kmymoney/mymoney -I/builddir/build/BUILD/kmymoney-5.2.2-build/kmymoney-5.2.2/kmymoney/mymoney/storage -I/builddir/build/BUILD/kmymoney-5.2.2-build/kmymoney-5.2.2/kmymoney/interfaces -I/builddir/build/BUILD/kmymoney-5.2.2-build/kmymoney-5.2.2/redhat-linux-build/kmymoney/interfaces -I/builddir/build/BUILD/kmymoney-5.2.2-build/kmymoney-5.2.2/kmymoney/plugins -I/builddir/build/BUILD/kmymoney-5.2.2-build/kmymoney-5.2.2/redhat-linux-build/kmymoney/plugins -I/builddir/build/BUILD/kmymoney-5.2.2-build/kmymoney-5.2.2/kmymoney/views -I/builddir/build/BUILD/kmymoney-5.2.2-build/kmymoney-5.2.2/kmymoney/dialogs -I/builddir/build/BUILD/kmymoney-5.2.2-build/kmymoney-5.2.2/kmymoney/converter -I/builddir/build/BUILD/kmymoney-5.2.2-build/kmymoney-5.2.2/redhat-linux-build/kmymoney/dialogs/settings -I/builddir/build/BUILD/kmymoney-5.2.2-build/kmymoney-5.2.2/redhat-linux-build/kmymoney/mymoney/storage -I/builddir/build/BUILD/kmymoney-5.2.2-build/kmymoney-5.2.2/redhat-linux-build/kmymoney/mymoney -I/builddir/build/BUILD/kmymoney-5.2.2-build/kmymoney-5.2.2/kmymoney/wizards/endingbalancedlg -I/builddir/build/BUILD/kmymoney-5.2.2-build/kmymoney-5.2.2/redhat-linux-build/kmymoney/wizards/endingbalancedlg -I/builddir/build/BUILD/kmymoney-5.2.2-build/kmymoney-5.2.2/kmymoney/wizards/newinvestmentwizard -I/builddir/build/BUILD/kmymoney-5.2.2-build/kmymoney-5.2.2/redhat-linux-build/kmymoney/wizards/newinvestmentwizard -I/builddir/build/BUILD/kmymoney-5.2.2-build/kmymoney-5.2.2/kmymoney/wizards/newloanwizard -I/builddir/build/BUILD/kmymoney-5.2.2-build/kmymoney-5.2.2/redhat-linux-build/kmymoney/wizards/newloanwizard -I/builddir/build/BUILD/kmymoney-5.2.2-build/kmymoney-5.2.2/kmymoney/wizards/wizardpages -I/builddir/build/BUILD/kmymoney-5.2.2-build/kmymoney-5.2.2/kmymoney/models -I/builddir/build/BUILD/kmymoney-5.2.2-build/kmymoney-5.2.2/redhat-linux-build/kmymoney/models -I/builddir/build/BUILD/kmymoney-5.2.2-build/kmymoney-5.2.2/kmymoney/icons -I/builddir/build/BUILD/kmymoney-5.2.2-build/kmymoney-5.2.2/redhat-linux-build/kmymoney/icons -I/builddir/build/BUILD/kmymoney-5.2.2-build/kmymoney-5.2.2/kmymoney/menus -I/builddir/build/BUILD/kmymoney-5.2.2-build/kmymoney-5.2.2/redhat-linux-build/kmymoney/menus -isystem /usr/include/qt6/QtCore -isystem /usr/include/qt6 -isystem /usr/lib64/qt6/mkspecs/linux-g++ -O2 -flto=auto -ffat-lto-objects -fexceptions -g -grecord-gcc-switches -pipe -Wall -Werror=format-security -Wp,-U_FORTIFY_SOURCE,-D_FORTIFY_SOURCE=3 -Wp,-D_GLIBCXX_ASSERTIONS -specs=/usr/lib/rpm/redhat/redhat-hardened-cc1 -fstack-protector-strong -specs=/usr/lib/rpm/redhat/redhat-annobin-cc1  -m64 -march=x86-64 -mtune=generic -fasynchronous-unwind-tables -fstack-clash-protection -fcf-protection -mtls-dialect=gnu2 -fno-omit-frame-pointer -mno-omit-leaf-frame-pointer -Wall -Wextra -Wcast-align -Wchar-subscripts -Wformat-security -Wno-long-long -Wpointer-arith -Wundef -Wnon-virtual-dtor -Woverloaded-virtual -Werror=return-type -Werror=init-self -Werror=undef -Wvla -Wdate-time -Wsuggest-override -Wlogical-op -pedantic -Wzero-as-null-pointer-constant -Wmissing-include-dirs -fexceptions -DNDEBUG -std=c++17 -fPIC -fvisibility=hidden -fvisibility-inlines-hidden   -UQT_NO_CAST_FROM_ASCII -UQT_NO_CAST_FROM_BYTEARRAY -UQT_NO_CAST_TO_ASCII -UQT_NO_CAST_TO_BYTEARRAY -Wall -Wextra -Wlogical-op -Wno-null-dereference -Wshadow -Wunused -Wno-misleading-indentation -Wsuggest-override -Wcast-qual -Wformat=2 -fno-common -Werror=return-type -Wzero-as-null-pointer-constant -MD -MT kmymoney/misc/CMakeFiles/kmm_gpgfile.dir/kmm_gpgfile_autogen/mocs_compilation.cpp.o -MF CMakeFiles/kmm_gpgfile.dir/kmm_gpgfile_autogen/mocs_compilation.cpp.o.d -o CMakeFiles/kmm_gpgfile.dir/kmm_gpgfile_autogen/mocs_compilation.cpp.o -c /builddir/build/BUILD/kmymoney-5.2.2-build/kmymoney-5.2.2/redhat-linux-build/kmymoney/misc/kmm_gpgfile_autogen/mocs_compilation.cpp

I think that 2cefa70 might have exposed the # elif __STDC_VERSION__ >= 201112L && !defined(__STDC_NO_THREADS__) line outside of # ifdef Py_BUILD_CORE causign this issue.

I don't know yet if there is some other thing that makes other g++ code work and not this one, perhaps it's just the -Werror=undef part. Other code in CPython uses defined(__STDC_VERSION__) && __STDC_VERSION__ .... Perhaps this needs the same treatment?

Fedora bug report: https://bugzilla.redhat.com/show_bug.cgi?id=2440571 (fixed by disabling the woob plugin).

CPython versions tested on:

3.15

Operating systems tested on:

Linux

Linked PRs

Activity

  1. hroncok
    added
    type-bugAn unexpected behavior, bug, or error
    on Jul 24, 2026

  2. hroncok commented on Jul 24, 2026

    @hroncok
    hroncok
    on Jul 24, 2026
    ContributorAuthor

    test.cpp

    #include <Python.h>
int main() { return 0; }
    $ g++ -I/usr/include/python3.15 -c -Werror=undef test.cpp
In file included from /usr/include/python3.15/Python.h:68,
                 from test.cpp:1:
/usr/include/python3.15/pyport.h:494:9: error: ‘__STDC_VERSION__’ is not defined, evaluates to ‘0’ [-Werror=undef]
  494 | #  elif __STDC_VERSION__ >= 201112L && !defined(__STDC_NO_THREADS__)
      |         ^~~~~~~~~~~~~~~~
cc1plus: some warnings being treated as errors

    This works with Python 3.14.

  3. hroncok
    added 2 commits that reference this issue on Jul 24, 2026

    pythongh-154643: Only use __STDC_VERSION__ when defined

    bebff64

    pythongh-154643: Only use __STDC_VERSION__ when defined

    19e8d7a

  4. hroncok commented on Jul 24, 2026

    @hroncok
    hroncok
    on Jul 24, 2026
    ContributorAuthor

    I'm working on a fix.

  5. StanFromIreland
    added
    buildThe build process and cross-build
    on Jul 25, 2026

  6. hroncok commented on Oct 29, 2026

    @hroncok
    hroncok
    on Oct 29, 2026
    ContributorAuthor

    Still happens in 3.15.2+ but now is different due to #160376 by @encukou

    $ g++ -I/usr/include/python3.15 -c -Werror=undef test.cpp
In file included from /usr/include/python3.15/Python.h:68,
                 from test.cpp:1:
/usr/include/python3.15/pyport.h:494:9: error: ‘_Py_STDC_VERSION’ is not defined, evaluates to ‘0’ [-Werror=undef]
  494 | #  elif _Py_STDC_VERSION >= 201112L && !defined(__STDC_NO_THREADS__)
      |         ^~~~~~~~~~~~~~~~
In file included from /usr/include/python3.15/Python.h:70:
/usr/include/python3.15/pymacro.h:29:9: error: ‘_Py_STDC_VERSION’ is not defined, evaluates to ‘0’ [-Werror=undef]
   29 |      && _Py_STDC_VERSION >= 201112L && _Py_STDC_VERSION <= 201710L
      |         ^~~~~~~~~~~~~~~~
cc1plus: some warnings being treated as errors
  7. hroncok
    added a commit that references this issue on Oct 29, 2026

    pythongh-154643: Only use _Py_STDC_VERSION when defined

    2363a51
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