C++ Accessing a class from a function it is not defined in - c++

Question

I'm new to C++ and having a bit of trouble with accessing variables inside a class. From what I've read on here so far creating globals is a really bad practice and not to do that, but I dont know how else to move access to a class around.
So far my searches have pointed me to set and get functions in the class, but I think I can only use them in the block where the object is defined.
Basically what I want to know is if I define a class object in main() then call a function in main like gameLoop() how do I access that object inside that new function without making the class object global.
For instance:
#include "stdafx.h"
#include <iostream>
using namespace std;
#include <string>
class Word
{
private:
string m_word;
int m_length;
public:
void set(string word, int length)
{
m_word = word;
m_length = length;
}
};
void gameLoop()
{
word1.set(); //flags error as it cant acces the word1 object
//I want to be able to access word1 from here
//Not a copy because that wouldnt change the actual word1
//I dont want to define it in here because then it would be created again
//for each loop of gameLoop
}
int main()
{
Word word1;
int play = 1;
while (play ==1){
gameLoop();
}
return 0;
}
This is a largely simplified version but for the purpose of the game I want the class to be stored externally but for a number of gameplay functions inside gameLoop to be able to access and change the class object.

Answer 1

Ideally, the dependencies of a function should be stater in the parameter list. If your gameLoop function requires a Word object, pass it in as an argument. That way, it's clear what objects the function requires to work. This would look something like:
void gameLoop(Word& word)
{
word.set();
// ^ Obviously you need to supply args here.
}
int main()
{
Word word1;
int play = 1;
while (play ==1){
gameLoop(word1);
}
return 0;
}
And since you're mutating the Word object in the function, you need to pass it by reference, or else you're just modifying a copy.
Your only other sane option would be to make the word object global, but that should be avoided at all costs. It makes testing more difficult since you need to take into consideration every change that may have happened, which makes it difficult to isolate problems.

Answer 2

If you're structuring you're program this way, you would have to pass it as a parameter to gameloop
However, This is a very poor design, since anything you create in main and want to access in gameloop would have to be passed in as an argument. I would consider a different approach.
You could move the entire loop and variable declarations into gameLoop as so:
void gameLoop()
{
Word word1;
int play = 1;
while (play ==1){
word1.set(/*args*/);
}
}
int main()
{
gameLoop();
return 0;
}
This way you won't have to pass a million things into gameloop. Generally in games there's some initialization and finalization that needs to take place as well, and this can all be done in main before/after the call to gameLoop.
So to answer you original question, you would have to pass word1 as an argument to gameLoop(). So redefine your function to accept a Word argument, and then pass in word1. but again, I would reconsider your current design before its too late