C++ header files and error relocation truncated to fit

Question

before I continue I'd like to tell you that I am new to programming (I've done a bit of python programming though but not that much).

I recently started learning C++ from YouTube videos and Sololearn.

I decided to start a project to train myself and I think that creating a python-like dictionary type is a good project (and maybe useful).

I created the Dictionary.h which contains the following code:

#ifndef DICTIONARY_H
#define DICTIONARY_H


class Dictionary { // Dictionary is a custom type that takes a key value(string required) and returns a value linked to it(int, string, bool are supported)
private:
  std::list<std::string> keyList;
  std::list<char> containerList; // I == int | S == string | B == bool
  std::list<int> indexingList; // contains the index of each value

  std::list<int> intVList;
  std::list<std::string> strVList;
  std::list<bool> boolVList;

  // private function for getting the last index from a value list
  int getLastIndex(char lType);
  int getKeyIndex(std::string key);
  char getContainerFromIndex(int indexNum);
  int getIndexFromKeyIndex(int indexNum);
  int _getValue(std::string key);
public:
  // constructor
  Dictionary();
  // add element to the dictionary
  void _add(std::string key, int value);
  void _add(std::string key, std::string value);
  void _add(std::string key, bool value);

  // get element from the dictionary using the key value
  int _get(std::string key);

  // check if a key exists in the dictionary
  bool keyInDict(std::string key);
};
#endif

and then I created the Dictionary.cpp with contains the following code (NOTE: the following is just a part of the code, have created all the mention functions from the header in the .cpp):

#include "Dictionary.h"
#include <iostream>
#include <string>
#include <list>

Dictionary::Dictionary() {
  std::cout << "Hello World";
}

void Dictionary::_add(std::string key, int value) {
  if (keyInDict(key)) {
    throw 9403;
  }
  char containerChar = 'I';
  keyList.push_back(key);
  containerList.push_back(containerChar);
  int atIndex = getLastIndex(containerChar);
  indexingList.push_back(atIndex+1);
  intVList.push_back(value);
}

int Dictionary::_getInt(std::string key) {
  int keyI = getKeyIndex(key);
  int realIndex = getIndexFromKeyIndex(keyI);
  if (getContainerFromIndex(keyI) != 'I') {throw 9400;}

  list<int>::iterator i = intVList.begin();

  advance(i, realIndex);
  return *i;
}

so I've written some code and now I want to test if it works so far (then I'll move forward to adding more functions.), so I created a run.cpp with the following content:

#include <iostream>
#include <string>
#include <list>
#include "Dictionary.h"

int main() {
  Dictionary dict;
  dict._add("test1", 1);
  dict._add("test2", 5);
  int got = dict._get("test1");
  std::cout << got;
  return 0;
}

but the compiler (CygWin g++ on windows 10 64 bit) throws this error:

$ g ++ run.cpp
/usr/lib/gcc/x86_64-pc-cygwin/10/../../../../x86_64-pc-cygwin/bin/ld: /tmp/cc7qwomO.o:run.cpp :(. text + 0x1e): undefined reference to `Dictionary :: Dictionary () '
/tmp/cc7qwomO.o:run.cpp:(.text+0x1e): relocation truncated to fit: R_X86_64_PC32 against undefined symbol `Dictionary :: Dictionary () '
/usr/lib/gcc/x86_64-pc-cygwin/10/../../../../x86_64-pc-cygwin/bin/ld: /tmp/cc7qwomO.o:run.cpp :(. text + 0x58): undefined reference to `Dictionary :: _ add (std :: string, int) '
/tmp/cc7qwomO.o:run.cpp:(.text+0x58): relocation truncated to fit: R_X86_64_PC32 against undefined symbol `Dictionary :: _ add (std :: string, int) '
/usr/lib/gcc/x86_64-pc-cygwin/10/../../../../x86_64-pc-cygwin/bin/ld: /tmp/cc7qwomO.o:run.cpp :(. text + 0xab): undefined reference to `Dictionary :: _ add (std :: string, int) '
/tmp/cc7qwomO.o:run.cpp:(.text+0xab): relocation truncated to fit: R_X86_64_PC32 against undefined symbol `Dictionary :: _ add (std :: string, int) '
/usr/lib/gcc/x86_64-pc-cygwin/10/../../../../x86_64-pc-cygwin/bin/ld: /tmp/cc7qwomO.o:run.cpp :(. text + 0xf9): undefined reference to `Dictionary :: _ get (std :: string) '
/tmp/cc7qwomO.o:run.cpp:(.text+0xf9): relocation truncated to fit: R_X86_64_PC32 against undefined symbol `Dictionary :: _ get (std :: string) '
collect2: error: ld returned output mode 1

#cause of my computer's language I had to pass the output through google translator so it may differ a bit from what you normally see

by the way, all files (Dictionary.h, Dictionary.cpp, run.cpp) are on the same directory

QUESTIONS

1. why do I get this error?
2. how can I fix it?
3. is there something I may not understand about including headers? do I need to link them with the cpp somehow?

ADDITIONAL INFO
I tried to edit the Dictionary.h and add the constructor body (an empty body like {}) and the first error about the Dictionary::Dictionary() did not appear(the rest appeared though). my guess is: it doesn't read the Dictionary.cpp, cause if I edit the main to just std::cout << 5; it works as expected (and in the error it says "undefined reference to ...")

Answer 1

The main file and the .cpp file must be linked before executing the main file. One solution is to create a makefile and run that. or Try This

This line creates the .o files of the cpp files

g++ -c main.cpp Dictionary.cpp

This code link both the .o files together

g++ main.o Dictionary.o