`std::is_integral_v` was introduced with C++17 (and is still there with C++20) So I think it has somehow picked the wrong C++ standard version. (Possibly accidentally still C++14?) Would it help if you would explicitly set the CMake variable [CXX\_STANDARD](https://cmake.org/cmake/help/v3.29/prop_tgt/CXX_STANDARD.html)? Or [CMAKE\_CXX\_STANDARD](https://cmake.org/cmake/help/v3.29/variable/CMAKE_CXX_STANDARD.html#variable:CMAKE_CXX_STANDARD)?
---
### Author:  [@edgar](https://discourse.itk.org/u/edgar)
#### Post date: [May 10, 2024, 4:49pm UTC](https://discourse.itk.org/t/how-to-build-itkelastix-with-itk-5-3-0-with-python-bindings-in-linux/6625/4 "2024-05-10T16:49:14Z")
Thank you both. I did some `grep`ping, and found that almost every cmake file had both `-std=c++20` and `-std=c++14`. For example,
```auto
./src/build/Modules/Core/Common/src/CMakeFiles/ITKCommon.dir/flags.make:9:
CXX_FLAGS = -std=c++20 -Wall -Wcast-align -Wdisabled-optimization -Wextra -Wformat=2 -Winvalid-pch -Wno-format-nonliteral -Wpointer-arith -Wshadow -Wunused -Wwrite-strings -funit-at-a-time -Wno-strict-overflow -Wno-deprecated -Wno-invalid-offsetof -Wno-undefined-var-template -Woverloaded-virtual -std=c++14 -fPIC
```
Then,
1. I deleted the `CMakeCache.txt` from `build_elastix`;
2. deleted both `=libomp` and `-std=c++14` from `build_elastix/Wrapping/Modules/Elastix/CMakeFiles/ElastixCastXML.dir/build.make`;
3. replaced
`set(INVALID_OPTIMIZATION_FLAGS "-fopenmp;-march=[a-zA-Z0-9\-]*;-mtune=[a-zA-Z0-9\-]*;-mfma")`
with
`set(INVALID_OPTIMIZATION_FLAGS "-fopenmp[a-zA-Z0-9\-=]*;-march=[a-zA-Z0-9\-]*;-mtune=[a-zA-Z0-9\-]*;-mfma;-std=c++14")`
in `insight-toolkit/Wrapping/macro_files/itk_auto_load_submodules.cmake:31`
4. added this to `insight-toolkit/Modules/ThirdParty/pygccxml/src/pygccxml/utils/utils.py::300`
```python
'-std=c++20': 201703,
'-std=gnu++20': 201703,
'-std=c++23': 202002,
'-std=gnu++23': 202002,
```
(based on `build/CMakeFiles/3.29.2/CompilerIdCXX/CMakeCXXCompilerId.cpp`),
5. and re-executed `make` inside `build_elastix`,
but it told me that
```auto
CMake Warning at CMakeLists.txt:109 (message):
Python wrapping of ITKElastix is known not to work with RelWithDebInfo
configuration. Release is recommended. Your CMAKE_BUILD_TYPE:
CMake Error at CMakeLists.txt:117 (include):
include could not find requested file:
ITKModuleExternal
```
Thus, I am going to retry again from the start (building ITK again) with those modifications, and see if it helps. I’ll report back later. Thanks.
[EDIT]
I am also adding this to `utils.py`:
```python
@property
def is_cxx20(self):
"""Returns true if -std=c++14 is being used"""
return self._cplusplus == cxx_standard.__STD_CXX['-std=c++20']
@property
def is_cxx20_or_greater(self):
"""Returns true if -std=c++14 or a newer standard is being used"""
return self._cplusplus >= cxx_standard.__STD_CXX['-std=c++20']
```
---
### Author:  [@dzenanz](https://discourse.itk.org/u/dzenanz)
#### Post date: [May 10, 2024, 5:05pm UTC](https://discourse.itk.org/t/how-to-build-itkelastix-with-itk-5-3-0-with-python-bindings-in-linux/6625/5 "2024-05-10T17:05:35Z")
> [@edgar](#):
>
> `"""Returns true if -std=c++14 is being used"""`
You might want to update the docstring to C++20.
---
### Author:  [@edgar](https://discourse.itk.org/u/edgar)
#### Post date: [May 10, 2024, 5:23pm UTC](https://discourse.itk.org/t/how-to-build-itkelastix-with-itk-5-3-0-with-python-bindings-in-linux/6625/6 "2024-05-10T17:23:12Z")
Thanks. The perks of yanking (if you know what I mean).
---
### Author:  [@edgar](https://discourse.itk.org/u/edgar)
#### Post date: [May 10, 2024, 5:30pm UTC](https://discourse.itk.org/t/how-to-build-itkelastix-with-itk-5-3-0-with-python-bindings-in-linux/6625/7 "2024-05-10T17:30:26Z")
Still no success. I also tried with
```bash
cmake "${_confopts[@]}"
find ./ -type f -exec grep -l '[-]std=c++14' \{\} + | parallel -q sed -i 's/ -std=c++14//g'
cmake --build build
```
To make sure that `-std=c++14` was removed. The error now is
```auto
[5%] Building C object Modules/ThirdParty/MINC/src/libminc/CMakeFiles/itkminc2.dir/libsrc2/dimension.c.o
In file included from /usr/src/googletest/src/gtest-all.cc:49:
In file included from /usr/src/googletest/src/gtest.cc:44:
/usr/lib64/gcc/x86_64-pc-linux-gnu/13.2.1/../../../../include/c++/13.2.1/chrono:2360:48: error: call to consteval function 'std::chrono::hh_mm_ss::_S_fractional_width' is not a constant expression
static constexpr unsigned fractional_width = {_S_fractional_width()};
^
/usr/lib64/gcc/x86_64-pc-linux-gnu/13.2.1/../../../../include/c++/13.2.1/chrono:2360:48: note: undefined function '_S_fractional_width' cannot be used in a constant expression
/usr/lib64/gcc/x86_64-pc-linux-gnu/13.2.1/../../../../include/c++/13.2.1/chrono:2315:2: note: declared here
_S_fractional_width()
^
```
I will now replace the flag `std=c++20` from `"${_confopts[@]}"` and let c++14 be
---
### Author:  [@edgar](https://discourse.itk.org/u/edgar)
#### Post date: [May 10, 2024, 5:57pm UTC](https://discourse.itk.org/t/how-to-build-itkelastix-with-itk-5-3-0-with-python-bindings-in-linux/6625/8 "2024-05-10T17:57:37Z")
> [@Niels\_Dekker](#):
>
> Would it help if you would explicitly set the CMake variable [CXX\_STANDARD](https://cmake.org/cmake/help/v3.29/prop_tgt/CXX_STANDARD.html)? Or [CMAKE\_CXX\_STANDARD](https://cmake.org/cmake/help/v3.29/variable/CMAKE_CXX_STANDARD.html#variable:CMAKE_CXX_STANDARD)?
I only tried with ITKElastix, but setting it with ITK alone yields:
```auto
INFO: Running CMake...
-- The CXX compiler identification is Clang 14.0.6
-- The C compiler identification is Clang 14.0.6
-- Detecting CXX compiler ABI info
CMake Error in build/CMakeFiles/CMakeScratch/TryCompile-HiLhj7/CMakeLists.txt:
Target "cmTC_687fb" requires the language dialect "CXX-std=c++20". But
the current compiler "Clang" does not support this, or CMake does not know
the flags to enable it.
CMake Error at /usr/share/cmake/Modules/CMakeDetermineCompilerABI.cmake:64 (try_compile):
Failed to generate test project build system.
Call Stack (most recent call first):
/usr/share/cmake/Modules/CMakeTestCXXCompiler.cmake:26 (CMAKE_DETERMINE_COMPILER_ABI)
CMakeLists.txt:46 (project)
```
The same thing happens with c++17. As a reminder, I am using clang14, because that is what ITK 5.3.0 needs. I will try to build again from scratch with c++14. What I did not try was to rebuild elastix (not ITKElastix) with that standard. I’ll check.
---
### Author:  [@edgar](https://discourse.itk.org/u/edgar)
#### Post date: [May 11, 2024, 12:32pm UTC](https://discourse.itk.org/t/how-to-build-itkelastix-with-itk-5-3-0-with-python-bindings-in-linux/6625/9 "2024-05-11T12:32:18Z")
I’ll give up on this. I concluded that it is not possible to achieve 5.3.0 with ITKElastix, so I went for 5.4rc03 (the latest compatible with elastix). The compilation of ITK tried to download VXL (VNL) without internet. To go around it, I had to build DCMTK and tried to build vxl, but it is currently not working ([Fails to build when dcmtk-3.6.5 is present: fatal error: 'dcistrma.h' file not found · Issue #768 · vxl/vxl · GitHub](https://github.com/vxl/vxl/issues/768) ; tested with mpicc and clang). I could check the building instructions of VXL inside of insight-toolkit, but I’ll just stop. Thanks.