Magick++ undefined reference to Magick::Image::Columns - c++

Question

Good day,
here is my code
#include <iostream>
#include <Magick++.h>
using namespace std;
using namespace Magick;
int main(int argc, char **argv) {
InitializeMagick(*argv);
Image image;
try {
image.read(argv[1]);
}
catch( Exception &error_ ) {
cout << "Caught exception: " << error_.what() << endl;
return 1;
}
int x = image.columns();
cout<<"your picture's width is "<< x << "px"<<endl;
return 0;
}
I use KDevelop(which uses CMake as builder),
when I try to compile the app, it throws me an error
main.cpp:25: undefined reference to `Magick::Image::columns() const'
Here's what my CMakeLists.txt contains.
cmake_minimum_required(VERSION 3.5)
project(hello)
set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -std=c++11")
set(SOURCE_FILES main.cpp)
add_executable(hello ${SOURCE_FILES})
add_definitions( -DMAGICKCORE_QUANTUM_DEPTH=16 )
add_definitions( -DMAGICKCORE_HDRI_ENABLE=0 )
find_package(ImageMagick COMPONENTS Magick++)
include_directories(${ImageMagick_INCLUDE_DIRS})
target_link_libraries(hello ${ImageMagick_LIBRARIES})
I figured out that there're often issues with undefined references when CMakeLists isn't written correctly, but I made it according to this About Magick++, how to write the CMakeLists?
where am I wrong? I can add any information needed.
UPD 1.
version of magick++,
8:6.8.9.9-7ubuntu5.7
system info:
Description: Linux Mint 18.1 Serena
UPD 2.
I just removed parenthesis and when tryed to compile with
size_t x = image.columns;
size_t y = image.rows;
KDevelop threw me
main.cpp:25:22: error: cannot convert ‘Magick::Image::columns’ from type ‘size_t (Magick::Image::)() const {aka long unsigned int (Magick::Image::)() const}’ to type ‘size_t {aka long unsigned int}’
even when
auto x = image.columns;
auto y = image.rows;
it throws
main.cpp:25:20: error: cannot convert ‘Magick::Image::columns’ from
type ‘size_t (Magick::Image::)() const {aka long unsigned int
(Magick::Image::)() const}’ to type ‘long unsigned int
(Magick::Image::*)() const’
what's happening?
P.S. hooray, this is my first question on stackoverflow! :-)

Answer 1

If you are able to compile your program without CMake using g++ main.cpp `Magick++-config --cxxflags --cppflags --ldflags --libs` (but for some reason cannot use ${ImageMagick_LIBRARIES} in CMake), then you can make use of Magick++-config in your CMakeLists.txt:
cmake_minimum_required(VERSION 3.5)
project(hello LANGUAGES CXX)
add_executable(hello main.cpp)
target_compile_features(hello PRIVATE cxx_std_11)
find_package(ImageMagick REQUIRED COMPONENTS Magick++)
target_compile_definitions(hello PRIVATE
MAGICKCORE_QUANTUM_DEPTH=16
MAGICKCORE_HDRI_ENABLE=0
)
target_include_directories(hello PRIVATE ${ImageMagick_INCLUDE_DIRS})
execute_process(COMMAND Magick++-config --ldflags
OUTPUT_VARIABLE ImageMagick_LINK_FLAGS
OUTPUT_STRIP_TRAILING_WHITESPACE
)
target_link_libraries(hello PRIVATE ${ImageMagick_LINK_FLAGS})
Here, execute_process allows us to get the result of Magick++-config --ldflags into a variable, which we can pass as flags to the linker through target_link_libraries.
Also, note how I've used target_compile_features rather than setting the global CMAKE_CXX_FLAGS variable, target_compile_definitions rather than add_definitions and target_include_directories rather than include_directories. It's better to use local (target-based) commands rather than modifying global state, both in programming and in CMake, since they can have unforeseen repercussions down the line -- in the context of CMake, those global commands would have affected nested sub-projects.

Answer 2

ForgottenUbrella 's version which I adapted didn't quite work for me, copying a line in from another project fixed it. Note, I'm using c++20 not 11.
I had the following error:
..... undefined reference to symbol 'pthread_create##GLIBC_2.2.5'
and the line that fixed it:
set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -std=c++2a -pthread")