CLion not compiling when Xcode does?

Question

I am doing a Udemy course on writing games in Unreal and learning C++ while you do. I was using CLion to write the code but when I try run it I get the following error;

/usr/local/bin/cmake --build /Users/penkin/Sandbox/penkin-unreal/Section_02/BullCowGame/cmake-build-debug --target BullCowGame -- -j 4
[ 50%] Linking CXX executable BullCowGame
Undefined symbols for architecture x86_64:
  "FBullCowGame::GetMaxTries()", referenced from:
      PlayGame() 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)
make[3]: *** [BullCowGame] Error 1
make[2]: *** [CMakeFiles/BullCowGame.dir/all] Error 2
make[1]: *** [CMakeFiles/BullCowGame.dir/rule] Error 2
make: *** [BullCowGame] Error 2

When I create the project in Xcode it compiles and runs fine using the exact same files.

My CLion Toolchains setup;

Files:

CMakeLists.txt

cmake_minimum_required(VERSION 3.10)
project(BullCowGame)

set(CMAKE_CXX_STANDARD 17)
add_executable(BullCowGame main.cpp)

FBullCowGame.h

#include <string>

class FBullCowGame {
public:
    void Reset();
    int GetMaxTries();
    int GetCurrentTry();
    bool IsGameWon();
    bool CheckGuessValidity(std::string);

private:
    int MyCurrentTry = 1;
    int MyMaxTries = 5;
};

FBullCowGame.cpp

#include "FBullCowGame.h"

void FBullCowGame::Reset() {}

int FBullCowGame::GetMaxTries() {
    return MyMaxTries;
}

int FBullCowGame::GetCurrentTry() {
    return MyCurrentTry;
}

bool FBullCowGame::IsGameWon() {
    return false;
}

bool FBullCowGame::CheckGuessValidity(std::string) {
    return false;
}

main.cpp

#include <iostream>
#include <string>
#include "FBullCowGame.h"

void PrintIntro();
std::string GetGuess();
void PlayGame();
bool AskToPlayAgain();

// --
// Application's entry point.
// --
int main() {
    do {
        PrintIntro();
        PlayGame();
    }
    while (AskToPlayAgain());

    return 0;  // Exit application.
}

// --
// Prints the game's intro text.
// --
void PrintIntro() {
    constexpr int WORD_LENGTH = 5;
    std::cout << "Welcome to Bulls & Cows, a fun word game." << std::endl;
    std::cout << "Can you guess the " << WORD_LENGTH << " letter isogram I'm thinking of?" << std::endl;
}

// --
// Gets the string guessed by the user and returns that string.
// --
std::string GetGuess() {
    std::string Guess;
    std::cout << std::endl << "Enter your guess:  ";
    getline(std::cin, Guess);
    return Guess;
}

// --
// Runs through the game logic.
// --
void PlayGame() {
    std::string Guess;
    FBullCowGame BCGame;
    int MaxTries = BCGame.GetMaxTries();

    for (int count = 1; count <= MaxTries; count++) {
        Guess = GetGuess();
        std::cout << "You guessed \"" << Guess << "\"" << std::endl;
    }
}

// --
// Asks the user if they would like to play the game again.
// --
bool AskToPlayAgain() {
    std::string Response;

    std::cout << std::endl << "Would you like to play again (y/n)? ";
    getline(std::cin, Response);

    return std::tolower(Response[0]) == 'y';
}

Answer 1

It is a linking and not a comiling error. The error:

Undefined symbols for architecture x86_64:
  "FBullCowGame::GetMaxTries()", referenced from:
      PlayGame() in main.cpp.o

Tells you that the linker was not able to find compiled code for FBullCowGame::GetMaxTries() that you try to use in PlayGame().

You need to add each cpp file you have to the list of source that has to be compiled, otherwise it won't be compiled:

add_executable(BullCowGame main.cpp FBullCowGame.cpp)

Answer 2

Thanks to @t.niese in the comments I've sorted the problem. In the CMakeLists.txt I need to add my FBullCowGame.cpp file.

New CMakeLists.txt

cmake_minimum_required(VERSION 3.10)
project(BullCowGame)

set(CMAKE_CXX_STANDARD 17)
add_executable(BullCowGame main.cpp FBullCowGame.cpp)