How do I get CMake to find OpenMP_C, OpenMP_CXX, etc.? - macos

Question

I am fairly new to working with the terminal and I am attempting to use cmake to configure a build for a project that involves public transportation routes. When I attempt to make the build I get the following response in the terminal:
$ cmake ..
-- Could NOT find OpenMP_C (missing: OpenMP_C_FLAGS OpenMP_C_LIB_NAMES)
-- Could NOT find OpenMP_CXX (missing: OpenMP_CXX_FLAGS OpenMP_CXX_LIB_NAMES)
-- Could NOT find OpenMP (missing: OpenMP_C_FOUND OpenMP_CXX_FOUND)
CMake Warning at CMakeLists.txt:33 (message):
Configuring without OpenMP!
CMake Error at src/CMakeLists.txt:13 (add_subdirectory):
The source directory
/Users/ericbush/Desktop/the-one/toolkit/gtfs/pfaedle/src/cppgtfs
does not contain a CMakeLists.txt file.
CMake Error at src/CMakeLists.txt:14 (add_subdirectory):
The source directory
/Users/ericbush/Desktop/the-one/toolkit/gtfs/pfaedle/src/configparser
does not contain a CMakeLists.txt file.
-- Configuring incomplete, errors occurred!
See also "/Users/ericbush/Desktop/the-one/toolkit/gtfs/pfaedle/build/CMakeFiles/CMakeOutput.log".
See also "/Users/ericbush/Desktop/the-one/toolkit/gtfs/pfaedle/build/CMakeFiles/CMakeError.log".
Below is what I believe to be the relevant code from the CMakeLists.txt file:
find_package(OpenMP)
if (OPENMP_FOUND)
set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} ${OpenMP_C_FLAGS}")
set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} ${OpenMP_CXX_FLAGS}")
endif()
# set compiler flags, see http://stackoverflow.com/questions/7724569/debug-vs-release-in-cmake
if(OPENMP_FOUND)
set(CMAKE_CXX_FLAGS "-fopenmp -Ofast -fno-signed-zeros -fno-trapping-math -Wall -Wno-format-extra-args -Wextra -Wformat-nonliteral -Wformat-security -Wformat=2 -Wextra -Wno-implicit-fallthrough -pedantic")
else()
message(WARNING "Configuring without OpenMP!")
set(CMAKE_CXX_FLAGS "-Ofast -fno-signed-zeros -fno-trapping-math -Wall -Wno-format-extra-args -Wextra -Wformat-nonliteral -Wformat-security -Wformat=2 -Wextra -Wno-implicit-fallthrough -pedantic")
endif()
set(CMAKE_CXX_FLAGS_DEBUG "-Og -g -DLOGLEVEL=3 -DPFAEDLE_DBG=1")
set(CMAKE_CXX_FLAGS_MINSIZEREL "${CMAKE_CXX_FLAGS} -DLOGLEVEL=2")
set(CMAKE_CXX_FLAGS_RELEASE "${CMAKE_CXX_FLAGS} -DLOGLEVEL=2")
set(CMAKE_CXX_FLAGS_RELWITHDEBINFO "${CMAKE_CXX_FLAGS} -g -DLOGLEVEL=3")
I have found some similar questions on this and other websites, but I am still struggling to understand the problem because I have never used cmake before and, as mentioned, I am somewhat new to working with the terminal. I would be extremely grateful for any information on what the error messages are actually telling me, or any suggestions on steps I could take/things I could try to solve the issue. I am working on a Mac, if anyone is wondering.

Answer 1

For the compiler to see OpenMP, you may need to set the following options in your cmake command (for dependencies located in /opt/local):
cmake .. \
-DOpenMP_C_FLAGS=-fopenmp=lomp \
-DOpenMP_CXX_FLAGS=-fopenmp=lomp \
-DOpenMP_C_LIB_NAMES="libomp" \
-DOpenMP_CXX_LIB_NAMES="libomp" \
-DOpenMP_libomp_LIBRARY="/opt/local/lib/libomp.dylib" \
-DOpenMP_CXX_FLAGS="-Xpreprocessor -fopenmp /opt/local/lib/libomp.dylib -I/opt/local/include" \
-DOpenMP_CXX_LIB_NAMES="libomp" \
-DOpenMP_C_FLAGS="-Xpreprocessor -fopenmp /opt/local/lib/libomp.dylib -I/opt/local/include"
The two missing CMakeLists.txt are located in git submodules within src/ To download the submodules, cd to the root phaedle directory and issue the following command:
git submodule update --init --recursive
Edit: this is now fixed in master.