Question

I’m trying to compile someone else’s C++ code. I have 0 experience with C++ myself. I’m using g++ on a MAC to compile one of the .cpp files that I received. When I do g++ main.cpp I get an Undefined symbols error. When googling the answers seem to be about a wrong link between files, but I don’t know how to link files.
How can I get the file to compile? I pasted the full code below.

Undefined symbols:
  "initializeFitness()", referenced from:
      runEvolution()     in ccZXBTDH.o
  "Grid::GetNeighbourhood(int, int, std::vector<Agent**, std::allocator<Agent**> >&)", referenced from:
      runEvolution()     in ccZXBTDH.o
      runEvolution()     in ccZXBTDH.o
      runEvolution()     in ccZXBTDH.o
  "Grid::Grid()", referenced from:
      runEvolution()     in ccZXBTDH.o
  "Reaper::GetAgentToKill()", referenced from:
      runEvolution()     in ccZXBTDH.o
  "Cupid::GetRandomBreeder()", referenced from:
      runEvolution()     in ccZXBTDH.o
  "Reaper::Select()", referenced from:
      runEvolution()     in ccZXBTDH.o
  "Grid::~Grid()", referenced from:
      runEvolution()     in ccZXBTDH.o
      runEvolution()     in ccZXBTDH.o
  "Breeder::Breed(Agent**, Agent**)", referenced from:
      runEvolution()     in ccZXBTDH.o
  "Cupid::Select()", referenced from:
      runEvolution()     in ccZXBTDH.o
  "Cupid::GetEmptyCell()", referenced from:
      runEvolution()     in ccZXBTDH.o
  "Agent::GetType()", referenced from:
      runEvolution()     in ccZXBTDH.o
      runEvolution()     in ccZXBTDH.o
      runEvolution()     in ccZXBTDH.o
      runEvolution()     in ccZXBTDH.o
  "Breeder::ProcessNeighbourhood(std::vector<Agent**, std::allocator<Agent**> > const&)", referenced from:
      runEvolution()     in ccZXBTDH.o
  "FateAgent::GetGenome(double*)", referenced from:
      runEvolution()     in ccZXBTDH.o
      runEvolution()     in ccZXBTDH.o
  "Cupid::GetParents()", referenced from:
      runEvolution()     in ccZXBTDH.o
  "Agent::IncreaseAge()", referenced from:
      runEvolution()     in ccZXBTDH.o
  "Grid::GetAgent(int, int)", referenced from:
      runEvolution()     in ccZXBTDH.o
      runEvolution()     in ccZXBTDH.o
      runEvolution()     in ccZXBTDH.o
      runEvolution()     in ccZXBTDH.o
      runEvolution()     in ccZXBTDH.o
      runEvolution()     in ccZXBTDH.o
      runEvolution()     in ccZXBTDH.o
      runEvolution()     in ccZXBTDH.o
      runEvolution()     in ccZXBTDH.o
      runEvolution()     in ccZXBTDH.o
      runEvolution()     in ccZXBTDH.o
      runEvolution()     in ccZXBTDH.o
      runEvolution()     in ccZXBTDH.o
      runEvolution()     in ccZXBTDH.o
      runEvolution()     in ccZXBTDH.o
      runEvolution()     in ccZXBTDH.o
  "FateAgent::GetSelectedCount()", referenced from:
      runEvolution()     in ccZXBTDH.o
      runEvolution()     in ccZXBTDH.o
  "Breeder::GetGenome(double*)", referenced from:
      runEvolution()     in ccZXBTDH.o
  "Agent::GetFitness()", referenced from:
      runEvolution()     in ccZXBTDH.o
      runEvolution()     in ccZXBTDH.o
      runEvolution()     in ccZXBTDH.o
  "Agent::~Agent()", referenced from:
      runEvolution()     in ccZXBTDH.o
  "Grid::DoMovement()", referenced from:
      runEvolution()     in ccZXBTDH.o
ld: symbol(s) not found
collect2: ld returned 1 exit status

Answer 1

I think you are trying to compile only a part of the entire program. Try g++ *.cpp
If it still doesnt work, It may be because your program needs an external library.