CMake: Undefined reference to function - c++

Question

I have following directory structure:
├── build (empty dir)
├── CMakeLists.txt
├── easylogging++.h
├── help.h
├── operation.h
├── operation_list.h
├── operations
│   ├── CMakeLists.txt
│   ├── matchcount.cc
│   └── matchcount.h
└── ops_toolkit.cc
And I am new to CMake and trying to write CMakeLists.txt.
My matchcount.h has a signature whose implementation is in matchcount.cc (as typical C/C++ structure).
Following is my CMakeLists.txt in base directory
cmake_minimum_required(VERSION 2.6)
project(ops_toolkit)
add_subdirectory(operations)
add_executable(ops_toolkit ops_toolkit.cc)
set(CMAKE_CXX_FLAGS "-std=c++0x")
and following is the one in operations directory
include_directories(${ops_toolkit_SOURCE_DIR}/operations)
link_directories(${ops_toolkit_BINARY_DIR}/operations)
set(all_operations_HEADER operations/matchcount.h)
set(all_operations_SOURCES operations/matchcount.cc)
I am getting undefined reference for function signature called int matchcount(int, const char**) and make complains following
dev:~/work/ops_toolkit/build$ make
Scanning dependencies of target ops_toolkit
[100%] Building CXX object CMakeFiles/ops_toolkit.dir/ops_toolkit.cc.o
Linking CXX executable ops_toolkit
CMakeFiles/ops_toolkit.dir/ops_toolkit.cc.o: In function `__static_initialization_and_destruction_0(int, int)':
ops_toolkit.cc:(.text+0x249): undefined reference to `operations::matchcount(int, char const**)'
collect2: ld returned 1 exit status
make[2]: *** [ops_toolkit] Error 1
make[1]: *** [CMakeFiles/ops_toolkit.dir/all] Error 2
make: *** [all] Error 2
Can someone help me with this?
Thanks

Answer 1

The problem comes from the add_subdirectory and its associated CMakeLists.txt (the one in ./operations), which is incorrect, see this SO question for the implications of the add_subdirectory command.
I also advise you to put include_directories and link_directories in the main CMake file, for clarity.