Undefined symbols when linking with g++? How do I solve this?

Question

my make file:

all: hPif clean

hPif : src/main.o src/fann_utils.o src/hashes.o src/Config.o
    g++ src/Config.o src/main.o src/fann_utils.o src/hashes.o  -lfann -L/usr/local/lib -o hPif

Config.o : src/Config.cpp src/Config.h
    g++ -c src/Config.cpp

hashes.o : src/hashes.cpp src/hashes.h
    g++ -c src/hashes.cpp

fann_utils.o: src/fann_utils.cpp fann_utils.h src/Config.h src/hashes.h
    g++ -c src/fann_utils.cpp 

main.o: src/main.cpp src/Config.h src/main.h src/hashes.h
    g++ -c src/main.cpp

clean: 
    rm -rf src/*o
    rm -rf *o

the error I get, upon make:

g++ src/Config.o src/main.o src/fann_utils.o src/hashes.o  -lfann -L/usr/local/lib -o hPif
Undefined symbols:
  "Config::NO_FILE_TRAIN", referenced from:
      _main in main.o
      _main in main.o
  "Config::LEARNING_RATE", referenced from:
      display_help()     in main.o
      train_network_no_file()     in main.o
      train_network()     in main.o
      _main in main.o
.
.
.

detail on code layout here: C++: I have this config class that I want to use between all my CPP files, how do I initialize it?

EDIT:

the code having issues here: http://pastebin.com/PDmHaDaC

Order matters with gcc linking related options. See, for instance http://stackoverflow.com/q/1095298/2509 or http://stackoverflow.com/q/2632505/2509. — dmckee --- ex-moderator kitten, Apr 01 '11 at 16:12
Also, as far as debugging `make` is concerned you can always try the offending command on the command line to see if it is make or your command that is causing the problem. — dmckee --- ex-moderator kitten, Apr 01 '11 at 16:13
Hmm, works for me. I did a small scale experiment and the order of Config.o and main.o does not matter on the link line. — quamrana, Apr 01 '11 at 16:51

score 2 · Accepted Answer · edited May 23 '17 at 11:55

2

I refer you to the accepted answer in the other question where the static variables are properly defined:

Source (Config.cpp):

#include "Config.h"

int Config::OUTPUT_TO_FILE = 0;
int Config::NEED_TO_TRAIN = 0;
int Config::NO_FILE_TRAIN = 0;
int Config::NEED_TO_TEST = 0;

Note the Config:: qualification to the variables.

Compare this to your paste bin page: http://pastebin.com/PDmHaDaC

edited May 23 '17 at 11:55

Community

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answered Apr 01 '11 at 17:05

quamrana

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score 0 · Answer 2 · answered Apr 01 '11 at 17:05

You have just learned from your other question the theory of how to handle these static member variables. Instead of immediately trying to hook them into a large codebase, try getting them to work in a small one; write a helloWorld that uses them, just a main.cpp that defines these variables, modifies them and prints them out. Once that's working you can move the definition into Config.cpp, and once that's working you can integrate these variables into your project.

EDIT:
Here's the trouble:

int NO_FILE_TRAIN = false;

should be

int Config::NO_FILE_TRAIN = false;

Undefined symbols when linking with g++? How do I solve this?

2 Answers2