How to configure QtCreator to use Clang 19 instead of GCC

Pete Carter

I have been trying to use the modules feature is C++ but somehow there is a problem in GCC (12.2.0)
Since i could not update GCC, i decided to switch to Clang

I downloaded Clang v19:

sudo apt install clang-19 clangd-19 clang-format-19 clang-tidy-19 clang-tools-19

In QtCreator, Preferences -> Kits
I cloned the Desktop GCC kit, then modified the following:

Compiler: /bin/clang-19
Debugger: /usr/bin/lldb-19
CMake Tool: /usr/bin/cmake

everything else is the same as GCC kit

In Preferences -> C++ -> Clangd

Path to executable: /usr/bin/clangd-19

In Preferences -> Analyzer -> Clang Tools

Clang-Tidy: /usr/bin/clang-tidy-19

Now everything should be configured correctly, that's what i thought ...

I have a problems i noticed so far, I cannot find any files i include, like iostream or cassert

Pete Carter

Tried adding the libraries in the include path in CMakeLists.txt

cmake_minimum_required(VERSION 3.25)

project(learn_cpp_33 LANGUAGES CXX)

set(CMAKE_CXX_STANDARD 23)
set(CMAKE_CXX_STANDARD_REQUIRED ON)

add_compile_options(-fmodules-ts)

add_executable(learn_cpp_33 src/main.cpp src/lib/helpers.cpp src/lib/data.cpp)

target_include_directories(
  learn_cpp_33 SYSTEM PRIVATE /usr/lib/llvm-19/include
                              /usr/lib/llvm-19/include/c++/v1)

include(GNUInstallDirs)

install(
  TARGETS learn_cpp_33
  LIBRARY DESTINATION ${CMAKE_INSTALL_LIBDIR}
  RUNTIME DESTINATION ${CMAKE_INSTALL_BINDIR})

But now i am getting a different error:

main.cpp:1:10: In included file: 'features.h' file not found
platform.h:35:12: error occurred here

I also don't want to keep editing the cmake file like that for every project, is there a way to add this include path system wide so that qtcreator can find it automatically ?

jsulm

@Pete-Carter said in How to configure QtCreator to use Clang 19 instead of GCC:

I have a problems i noticed so far, I cannot find any files i include, like iostream or cassert

Does the project compile?
These errors you show could come from the code model.

Pete Carter

@jsulm

When i restarted the IDE, and changed the kit to clang, it now compiles.
it compiles well without trying to use modules.

However when i try to add modules support by adding add_compile_options(-fmodules-ts) in CMakeLists.txt

cmake_minimum_required(VERSION 3.16)

project(learn_cpp_7 LANGUAGES CXX)

set(CMAKE_CXX_STANDARD 23)
set(CMAKE_CXX_STANDARD_REQUIRED ON)

add_compile_options(-fmodules-ts)

add_executable(learn_cpp_7 src/main.cpp src/lib/helpers.hpp src/lib/helpers.cpp
                           src/lib/data.hpp src/lib/data.cpp src/module_0.cpp)

include(GNUInstallDirs)
install(
  TARGETS learn_cpp_7
  LIBRARY DESTINATION ${CMAKE_INSTALL_LIBDIR}
  RUNTIME DESTINATION ${CMAKE_INSTALL_BINDIR})

I get this error:

main.cpp:4:10: 'bitset' file not found

The toolchain supposed to be in /usr/lib/llvm-19/

cristian-adam

The issue is tracked at https://bugreports.qt.io/browse/QTCREATORBUG-28465

clangd doesn't currently support C++20's modules. See also https://github.com/clangd/clangd/issues/1293

It looks like progress is being made though.

Pete Carter

@cristian-adam

Thanks man