QtCreator does not recognize omp.h even though the program compiles and it can be run with g++

Sampo Paukkonen

I am using QtCreator and CMake for C++ development. My CMakeLists.txt file is currently the following:

"""

cmake_minimum_required(VERSION 3.9)

project(my_project LANGUAGES CXX)

set(CMAKE_CXX_STANDARD 20)
set(CMAKE_CXX_STANDARD_REQUIRED ON)
set(CMAKE_CXX_FLAGS_RELEASE "-O3")

add_executable(my_project main.cpp)

find_package(OpenMP)
target_link_libraries(my_project PUBLIC OpenMP::OpenMP_CXX)

"""

When I try to use OpenMPs functions such as the omp_get_num_threads(), I get the semantic issue:
"""
main.cpp:355:21: error: use of undeclared identifier 'omp_get_num_threads'
"""

caused by the error that for some reason, the header file omp.h cannot be found:
"""
main.cpp:10:10: error: 'omp.h' file not found
"""

However, I can run the program without any errors and the output does not seem exhibit undefined behavior. Compiling from the command line works as well e.g. by
"""
g++ main.cpp -fopenmp -std=c++20
"""

What could be the root cause for this problem?

sierdzio

Move add_executable line after you find_package. Not sure if it will help, but it might.

cristian-adam

Which version of Qt Creator are you using? clangd needs to be build with the openmp module enabled.

You should check if you have qtcreator/libexec/qtcreator/clang/lib/clang/17/include/omp.h in your Qt Creator installation.

The official https://download.qt.io/official_releases/qtcreator/13.0/ Qt Creator binaries all have right clangd and omp.h header.

Sampo Paukkonen

@sierdzio

For future reference, this did not solve the issue.