CMake build error - missing vtable for virtual method error - c++

Question

Our Xcode C++ project is being converted to a CMake script. When building the CMake script, a missing vtable error keeps happening, if I use a class with virtual functions in my dummy main. If I only use a class without virtual functions in my main, everything builds fine.
The project builds fine for Xcode. What am I missing with my CMake script?
The CMake file:
cmake_minimum_required(VERSION 3.0)
add_compile_options(-std=c++17)
SET (PROJECT_SOURCE_DIR "${CMAKE_SOURCE_DIR}/source")
include_directories(
"${PROJECT_SOURCE_DIR}/"
"${PROJECT_SOURCE_DIR}/main/"
"${PROJECT_SOURCE_DIR}/lib/hopscotch-map/"
"${PROJECT_SOURCE_DIR}/lib/rapidjson/"
)
add_executable(TestProject "${PROJECT_SOURCE_DIR}/main/dummy-main.cpp")
install(TARGETS TestProject DESTINATION bin)
Main file:
#include <stdio.h>
#include "Player.hpp"
int main(int argc, char **argv) {
auto player = Player{"John"};
return 0;
}
The logs:
jess$ gmake -j 8 VERBOSE=1
/usr/local/Cellar/cmake/3.13.3/bin/cmake -S/Users/jess/TestProject -B/Users/jess/TestProject --check-build-system CMakeFiles/Makefile.cmake 0
/usr/local/Cellar/cmake/3.13.3/bin/cmake -E cmake_progress_start /Users/jess/TestProject/CMakeFiles /Users/jess/TestProject/CMakeFiles/progress.marks
gmake -f CMakeFiles/Makefile2 all
gmake[1]: Entering directory '/Users/jess/TestProject'
gmake -f CMakeFiles/TestProject.dir/build.make CMakeFiles/TestProject.dir/depend
gmake[2]: Entering directory '/Users/jess/TestProject'
cd /Users/jess/TestProject && /usr/local/Cellar/cmake/3.13.3/bin/cmake -E cmake_depends "Unix Makefiles" /Users/jess/TestProject /Users/jess/TestProject /Users/jess/TestProject /Users/jess/TestProject /Users/jess/TestProject/CMakeFiles/TestProject.dir/DependInfo.cmake --color=
Dependee "source/BaseEntity.hpp" is newer than depends file "/Users/jess/TestProject/CMakeFiles/TestProject.dir/depend.internal".
Clearing dependencies in "/Users/jess/TestProject/CMakeFiles/TestProject.dir/depend.make".
Scanning dependencies of target TestProject
gmake[2]: Leaving directory '/Users/jess/TestProject'
gmake -f CMakeFiles/TestProject.dir/build.make CMakeFiles/TestProject.dir/build
gmake[2]: Entering directory '/Users/jess/TestProject'
[ 50%] Building CXX object CMakeFiles/TestProject.dir/source/main/dummy-main.cpp.o
/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/c++ -I/Users/jess/TestProject -I/Users/jess/TestProject/source -I/Users/jess/TestProject/source/lib/hopscotch-map -I/Users/jess/TestProject/source/lib/rapidjson -isysroot /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.14.sdk -std=c++17 -fPIC -fexceptions -g -O3 -o CMakeFiles/TestProject.dir/source/main/dummy-main.cpp.o -c /Users/jess/TestProject/source/main/dummy-main.cpp
[100%] Linking CXX executable TestProject
/usr/local/Cellar/cmake/3.13.3/bin/cmake -E cmake_link_script CMakeFiles/TestProject.dir/link.txt --verbose=1
/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/c++ -isysroot /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.14.sdk -Wl,-search_paths_first -Wl,-headerpad_max_install_names CMakeFiles/TestProject.dir/source/main/dummy-main.cpp.o -o TestProject
Undefined symbols for architecture x86_64:
"Player::Player(std::__1::basic_string_view<char, std::__1::char_traits<char> >)", referenced from:
_main in dummy-main.cpp.o
"vtable for BaseEntity", referenced from:
Player::~Player() in dummy-main.cpp.o
NOTE: a missing vtable usually means the first non-inline virtual member function has no definition.
"vtable for Player", referenced from:
Player::~Player() in dummy-main.cpp.o
NOTE: a missing vtable usually means the first non-inline virtual member function has no definition.
ld: symbol(s) not found for architecture x86_64
clang: error: linker command failed with exit code 1 (use -v to see invocation)
gmake[2]: *** [CMakeFiles/TestProject.dir/build.make:84: TestProject] Error 1
gmake[2]: Leaving directory '/Users/jess/TestProject'
gmake[1]: *** [CMakeFiles/Makefile2:73: CMakeFiles/TestProject.dir/all] Error 2
gmake[1]: Leaving directory '/Users/jess/TestProject'
gmake: *** [Makefile:130: all] Error 2

Answer 1

The clue is buried in the linker output:
Undefined symbols for architecture x86_64:
"Player::Player(std::__1::basic_string_view<char, std::__1::char_traits<char> >)", referenced from:
_main in dummy-main.cpp.o
"vtable for BaseEntity", referenced from:
Player::~Player() in dummy-main.cpp.o
NOTE: a missing vtable usually means the first non-inline virtual member function has no definition.
"vtable for Player", referenced from:
Player::~Player() in dummy-main.cpp.o
NOTE: a missing vtable usually means the first non-inline virtual member function has no definition.
Which immediately alerts me that you forgot to link the compilation unit containing the definitions of these functions.
Assuming that Player is defined in player.hpp and player.cpp and that they are in the subdirectory src then my suggestion would be to update the add_executable call to:
add_executable(TestProject "${PROJECT_SOURCE_DIR}/main/dummy-main.cpp" src/player.hpp src/player.cpp)
Note that the "current source or binary directory" is assumed here and there is no need to spell it out.
Also note that I have included the header file as part of the target. There are a number of advantages to this:
when generating project files for visual studio, xcode etc, these file will appear in the project tree.
When using the latest INSTALL commands, these files can be given properties to ensure that they are treated properly (e.g. public or private header files for library targets)