Undefined symbols when actually including. Broken compiler/IDE? - c++

Question

I'm testing the CLion IDE, and I'm attempting to write a minimal C++ program. Here's my code:
in main.cpp:
#include "classings.h"
int main() {
classings s;
s.doSomething();
return 0;
}
in classings.h:
class classings {
public:
void doSomething();
};
in classings.cpp:
#include <string>
#include <iostream>
#include "classings.h"
void classings::doSomething() {
std::cout << "hei" << std::endl;
}
I have no clue why this gives me this error:
Undefined symbols for architecture x86_64:
"classings::doSomething()", referenced from:
_main in main.cpp.o
ld: symbol(s) not found for architecture x86_64
clang: error: linker command failed with exit code 1 (use -v to see invocation)
I'm on OSX 10.10.

Answer 1

I think that your source files classings.h and classings.cpp are not included within your CMakeLists.txt.
If you open CMakeLists.txt, it should look something like this:
Incomplete CMakeLists.txt
cmake_minimum_required(VERSION 2.8.4)
project(untitled)
set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -std=c++11")
set(SOURCE_FILES main.cpp) # your other source files aren't listed
add_executable(my-program ${SOURCE_FILES})
You can fix the problem by including the new source files
Correct CMakeLists.txt
cmake_minimum_required(VERSION 2.8.4)
project(untitled)
set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -std=c++11")
set(SOURCE_FILES main.cpp classings.hpp classings.cpp) # manually listing all sources
add_executable(my-program ${SOURCE_FILES})
FYI, you can save yourself the hassle of editing the CMakeLists.txt every time you add/remove a new source file by using the file() or aux_source_directory() command. Here's an example:
set(SOURCE_DIRECTORY "src")
file(GLOB_RECURSE SOURCE_FILES "${SOURCE_DIRECTORY}/*.c" "${SOURCE_DIRECTORY}/*.h"
"${SOURCE_DIRECTORY}/*.cc" "${SOURCE_DIRECTORY}/*.hh"
"${SOURCE_DIRECTORY}/*.cpp" "${SOURCE_DIRECTORY}/*.hpp"
"${SOURCE_DIRECTORY}/*.cxx" "${SOURCE_DIRECTORY}/*.hxx")
add_executable(my-program ${SOURCE_FILES})
Or
aux_source_directory("src" SOURCE_FILES)
add_executable(my-program ${SOURCE_FILES})