# Intel oneApi C++ Compiler with Visual Studio 2022
**URL:** https://discourse.cmake.org/t/intel-oneapi-c-compiler-with-visual-studio-2022/6634
**Category:** Usage
**Tags:** os:windows, comp:intel
**Created:** [October 9, 2022, 4:01pm UTC](https://discourse.cmake.org/t/intel-oneapi-c-compiler-with-visual-studio-2022/6634 "2022-10-09T16:01:40Z")
**Posts on this page:** 8
**Page:** 1
### Author:  [@EagleDad](https://discourse.cmake.org/u/EagleDad)
#### Post date: [October 9, 2022, 4:01pm UTC](https://discourse.cmake.org/t/intel-oneapi-c-compiler-with-visual-studio-2022/6634/1 "2022-10-09T16:01:40Z")
Hello,
I’m using CMake 3.23.1 with Visual Studio 2022 and the Intel oneApi C++ Compiler 2022. Everything works fine, but I have some trouble with changing some compiler flags for individual projects.
I want to change the optimization from O2 to O3 but I’m not able to get it work. And I also want do enable the optimization output from the Intel compiler.
Overwriting the `CMAKE_CXX_FLAGS` does not work.
```auto
set(CMAKE_CXX_FLAGS_RELEASE "/MD /O3 /DNDEBUG /O3 /Qopt-report:3 " PARENT_SCOPE)
```
Adding compile option by `add_compile_options("/Qopt-report:3")` also does not work.
I also tried to set options specific by target, but it also does not work `target_compile_options( ${LIBRARY_NAME_RAW} PUBLIC /O3)`.
What am I doing wrong?
Thanks and best regards,
Dirk
---
### Author:  [@ben.boeckel](https://discourse.cmake.org/u/ben.boeckel)
#### Post date: [October 9, 2022, 9:47pm UTC](https://discourse.cmake.org/t/intel-oneapi-c-compiler-with-visual-studio-2022/6634/2 "2022-10-09T21:47:16Z")
The `PARENT_SCOPE` seems odd to me. Can you reproduce this in a simple example just to make sure nothing else in the project is interfering?
---
### Author:  [@EagleDad](https://discourse.cmake.org/u/EagleDad)
#### Post date: [October 10, 2022, 6:51am UTC](https://discourse.cmake.org/t/intel-oneapi-c-compiler-with-visual-studio-2022/6634/3 "2022-10-10T06:51:52Z")
Hi Ben,
thanks for the feedback.
Here is a minimum example that shows the behavior.
```auto
project(IntelTest)
set(EXECUTABLE_NAME intelTest)
cmake_minimum_required(VERSION 3.22)
set(CMAKE_CONFIGURATION_TYPES "Debug;Release")
set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -std:c++17 -Qopt-report:3 -O3")
add_executable(${EXECUTABLE_NAME}
main.cpp
)
```
The C++ standard is set, but the optimization flag is still /O2
---
### Author:  [@ben.boeckel](https://discourse.cmake.org/u/ben.boeckel)
#### Post date: [October 10, 2022, 1:23pm UTC](https://discourse.cmake.org/t/intel-oneapi-c-compiler-with-visual-studio-2022/6634/4 "2022-10-10T13:23:18Z")
It looks like the `-O2` flag comes from `CMAKE_CXX_FLAGS_RELEASE`, so that variable would need to be edited:
```cmake
string(REPLACE "/O2" "" CMAKE_CXX_FLAGS_RELEASE "${CMAKE_CXX_FLAGS_RELEASE}")
```
---
### Author:  [@EagleDad](https://discourse.cmake.org/u/EagleDad)
#### Post date: [October 10, 2022, 1:53pm UTC](https://discourse.cmake.org/t/intel-oneapi-c-compiler-with-visual-studio-2022/6634/5 "2022-10-10T13:53:02Z")
I found something similar and now I think it is an issue with the Intel C++ compiler and Visual Studio.
Visual Studio support Od, O1, O2 and Ox.
The Intel compiler supports Od, O1, O2, Ox and O3[Intel C++].
With
```auto
MESSAGE(STATUS "CMAKE_CXX_FLAGS_RELEASE: ${CMAKE_CXX_FLAGS_RELEASE}")
string(REGEX REPLACE "/O[0-4]" "/O3" CMAKE_CXX_FLAGS_RELEASE "${CMAKE_CXX_FLAGS_RELEASE}")
set(CMAKE_CXX_FLAGS_RELEASE "${CMAKE_CXX_FLAGS_RELEASE}" CACHE STRING "" FORCE)
MESSAGE(STATUS "CMAKE_CXX_FLAGS_RELEASE: ${CMAKE_CXX_FLAGS_RELEASE}")
```
I can change to all possible values for the optimization that are supported by Visual Studio, but I cannot set the value to O3, also the CXX\_FLAGS in the CMake window state that O3 is set. In Visual Studio it is still O2
---
### Author:  [@EagleDad](https://discourse.cmake.org/u/EagleDad)
#### Post date: [October 10, 2022, 2:51pm UTC](https://discourse.cmake.org/t/intel-oneapi-c-compiler-with-visual-studio-2022/6634/6 "2022-10-10T14:51:08Z")
If I use Ninja to build the project, the flags for optimization are accepted. So I think there must be a connection to Visual Studio. Changing the values in Visual Studio directly work, but not with CMake.
---
### Author:  [@ben.boeckel](https://discourse.cmake.org/u/ben.boeckel)
#### Post date: [October 10, 2022, 6:00pm UTC](https://discourse.cmake.org/t/intel-oneapi-c-compiler-with-visual-studio-2022/6634/7 "2022-10-10T18:00:22Z")
Hmm. I suspect this is just CMake not knowing what fields correlate with Intel compiler flags that well. Please file [an issue](https://gitlab.kitware.com/cmake/cmake/-/issues) about this.
---
### Author:  [@EagleDad](https://discourse.cmake.org/u/EagleDad)
#### Post date: [October 11, 2022, 5:55am UTC](https://discourse.cmake.org/t/intel-oneapi-c-compiler-with-visual-studio-2022/6634/8 "2022-10-11T05:55:43Z")
Thanks for your hints right now.
The issue is created and can be found here:
[https://gitlab.kitware.com/cmake/cmake/-/issues/24045](https://gitlab.kitware.com/cmake/cmake/-/issues/24045)