C++ extern array declared in header not usable in main.cpp

Question

I am a beginner in C++ so it's more than likely that my problem is extremely easy to solve. My problem is that I am trying to declare an array in my header file, but i can`t acces it in my main.cpp unit. The error message that keeps printing is:"initializing: cannot convert from 'int' to 'int [6]'

This is the code in my header file:

#pragma once

extern int Guess[6] = 0;

void Input(){
    std::cout << "Please enter your 6 numbers in the range of 1-49 line by line:" << std::endl;
    for (int i = 0; i < 6; i++){
        std::cin >> Guess[i];
        for (int i1 = 0; i1 < 6; i1++){
            if (Guess[i1] > 50){
                std::cout << "Your number is not in the range!!! Try again please:" << std::endl;
                Guess[i1] = 0;
                std::cin >> Guess[1];

            }
        }

    }

    std::cout << Guess[0] << std::endl;
    std::cout << Guess[1] << std::endl;
    std::cout << Guess[2] << std::endl;
    std::cout << Guess[3] << std::endl;
    std::cout << Guess[4] << std::endl;
    std::cout << Guess[5] << std::endl;
}

And this is the code in main.cpp:

#include "stdafx.h"
#include <iostream>
#include "Input.h"

int main(){

    int Guess[6];
    Input();
    return 0;
}

Thanks for any potential help.

Move int Guess[6]; outside of the main() function body and drop the = 0 in the declaration. — user0042
– user0042, Commented Sep 3, 2017 at 11:30
If you're using headers, only include declarations or inline definitions in them. Guess and Input should only be declared, with their definitions resting in a separate cpp file; Especially drop the = 0 part on Guess. — Cubic
– Cubic, Commented Sep 3, 2017 at 11:33
instead of array use std::array<int, 6> and pass it as a parameter (by reference) to your function - so you will not need extern or global variables — Artemy Vysotsky
– Artemy Vysotsky, Commented Sep 3, 2017 at 11:35

Raindrop7 · Accepted Answer · 2017-09-03 13:08:15Z

2

You should not initialize an external array but only forward declare it. So you can declare it like this:

extern int Guess[6];

And in the another file you should define it globally:

//source.cpp

int Guess[6]; // Remove the keyword `extern` here and you must specify the size here.

void DoSomeThing(){

    // now you can use it here
    Guess[0] = 0; // eg
}

You can also declare the external array without specifying the size:

// input.h

extern int bigIntArray[];

// source.cpp

int Guess[6];

void DoSomething(){

    // Do some staff on the array.
}

This inform the compiler that the array is defined somewhere else.

answered Sep 3, 2017 at 13:08

Raindrop7

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1 Comment

Heinz Muller Over a year ago

Thank you very much for your help!

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