Compiling from multiple files gives "undefined reference" - c++

Question

I need to provide a CFG class in a separate file, but I'm unsure how to compile it together with the associated .h and the main program.
I've #includeed the .h file and I've asked for both files at the command line, but I'm not sure why this is wrong for compiling them together.
Thoughts?
CFG.cpp:
#include <iostream>
#include <stdio.h>
#include <string>
using namespace std;
class CFG
{
public:
string code[25];
char startNT;
//private:
CFG(string inCode[], int stringLen)
{
for (int a = 0; a < stringLen; a++)
{
//cout << inCode[a] << endl;
this->code[a] = inCode[a];
}
for (int a = 0; a < stringLen; a++)
{
cout << this->code[a] << endl;
}
}
char getStartNT()
{
return startNT;
}
void setStartNT(char stNT)
{
startNT = stNT;
}
bool processData(string inString, string wkString)
{
//Our recursive function
return true;
}
void garbage()
{
return;
}
};
CFG.h:
#ifndef _cfg_h_
#define _cfg_h_
#include <iostream>
#include <stdio.h>
#include <string>
using namespace std;
class CFG
{
public:
string code[25];
char startNT;
CFG(string inCode[], int stringLen);
char getStartNT();
void setStartNT(char stNT);
bool ProcessData(string inString, string wkString);
void garbage();
};
#endif
cfg_entry.cpp:
#include <stdio.h>
#include <iostream>
#include "cfg.h"
using namespace std;
int main()
{
string inArray[5];
inArray[0] = "test0";
inArray[1] = "test1";
inArray[2] = "test2";
inArray[3] = "test3";
inArray[4] = "test4";
CFG * cfg1 = new CFG(inArray, 5);
cfg1->garbage();
return 0;
}
Compile errors:
art#tv:~/Dropbox/Weber/CS 4110/Individual Assignment 2$ g++ -g -std=c++11 -Wall -o cfg_entry cfg.cpp cfg_entry.cpp
/tmp/ccICQEd0.o: In function `main':
/home/art/Dropbox/Weber/CS 4110/Individual Assignment 2/cfg_entry.cpp:15: undefined reference to `CFG::CFG(std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >*, int)'
/home/art/Dropbox/Weber/CS 4110/Individual Assignment 2/cfg_entry.cpp:16: undefined reference to `CFG::garbage()'
collect2: error: ld returned 1 exit status

Answer 1

I found my issue. In my case, the header file was defining the class and the .cpp file was re-defining it again, trying to create 2 instances of the CFG class. The .h needed to handle the class declaration and variable instantiation while the .cpp handles only the function definitions.
cfg.h:
#ifndef _cfg_h_
#define _cfg_h_
#include <iostream>
#include <stdio.h>
#include <string>
using namespace std;
class CFG
{
private:
string code[25];
char startNT;
public:
CFG(string inCode[], int stringLen);
char getStartNT();
void setStartNT(char stNT);
bool processData(string inString, string wkString);
void garbage();
};
#endif
cfg.cpp:
#include <iostream>
#include <stdio.h>
#include <string>
#include "cfg.h"
using namespace std;
CFG::CFG(string inCode[], int stringLen)
{
for (int a = 0; a < stringLen; a++)
{
//cout << inCode[a] << endl;
this->code[a] = inCode[a];
}
for (int a = 0; a < stringLen; a++)
{
cout << this->code[a] << endl;
}
}
char CFG::getStartNT()
{
return startNT;
}
void CFG::setStartNT(char stNT)
{
startNT = stNT;
}
bool CFG::processData(string inString, string wkString)
{
//Our recursive function
return true;
}
void CFG::garbage()
{
return;
}