Cmake not changing build flags - cmake

Question

Consider the following simple openMP program:
program hello
use OMP_LIB
implicit none
integer :: nthreads, tid
!$OMP PARALLEL PRIVATE(nthreads, tid)
tid = omp_get_thread_num()
nthreads = omp_get_num_threads()
! print *, "hello"
print *,"Thread:", tid, "of", nthreads
!$OMP END PARALLEL
end program hello
when i compile it as
gfortran -fopenmp hello.90 -o hello.x
I get output as:
Thread: 2 of 4
Thread: 1 of 4
Thread: 0 of 4
Thread: 3 of 4
as expected.
Now if i consider the following CMakeLists.txt file
cmake_minimum_required(VERSION 2.8.9)
project (hello Fortran)
enable_language(Fortran)
IF(NOT CMAKE_BUILD_TYPE)
message("NO BUILD TYPE PROVIDED")
message("DEFAULT BUILD TYPE SET TO 'Release'")
set(CMAKE_BUILD_TYPE 'Release')
ENDIF()
IF(${CMAKE_BUILD_TYPE} MATCHES RELEASE OR ${CMAKE_BUILD_TYPE} MATCHES Release)
message("MAKING RELEASE BUILD")
set(CMAKE_Fortran_FLAGS_RELEASE "-fopenmp")
message("FLAGS: ${CMAKE_Fortran_FLAGS_RELEASE}")
ENDIF()
add_executable(hello.x hello.f90)
Considering above file is right, it should add omp flag to make file and hence compile and run same, however
$ mkdir build; cd build
$ cmake ..
-- The Fortran compiler identification is GNU 6.1.0
-- Checking whether Fortran compiler has -isysroot
-- Checking whether Fortran compiler has -isysroot - yes
-- Checking whether Fortran compiler supports OSX deployment target flag
-- Checking whether Fortran compiler supports OSX deployment target flag - yes
-- Check for working Fortran compiler: /usr/local/bin/gfortran
-- Check for working Fortran compiler: /usr/local/bin/gfortran - works
-- Detecting Fortran compiler ABI info
-- Detecting Fortran compiler ABI info - done
-- Checking whether /usr/local/bin/gfortran supports Fortran 90
-- Checking whether /usr/local/bin/gfortran supports Fortran 90 - yes
NO BUILD TYPE PROVIDED
DEFAULT BUILD TYPE SET TO 'Release'
MAKING RELEASE BUILD
FLAGS: -fopenmp
-- Configuring done
-- Generating done
-- Build files have been written to: /Users/user/Programs/omp/build
$
$ make
Scanning dependencies of target hello.x
[ 50%] Building Fortran object CMakeFiles/hello.x.dir/hello.f90.o
[100%] Linking Fortran executable hello.x
Undefined symbols for architecture x86_64:
"_omp_get_num_threads_", referenced from:
_MAIN__ in hello.f90.o
"_omp_get_thread_num_", referenced from:
_MAIN__ in hello.f90.o
ld: symbol(s) not found for architecture x86_64
collect2: error: ld returned 1 exit status
make[2]: *** [hello.x] Error 1
make[1]: *** [CMakeFiles/hello.x.dir/all] Error 2
Which is same as missing -fopenmp flag. How to add it?

Answer 1

The set command for CMAKE_BUILD_TYPE take a "non-string" argument apparently.
Changing
set(CMAKE_BUILD_TYPE 'Release')
to
set(CMAKE_BUILD_TYPE Release)
solved the problem for me. I first dug into the cache system to understand why your setting would not work and there was no reason. I found a CMAKE_Fortran_FLAGS_'Release' entry in ccmake and looked again at the variable CMAKE_BUILD_TYPE in the docs, and it takes values empty, Debug, Release, RelWithDebInfo, MinSizeRel (which I understood as being unquoted).