How to call an array in the main function from a class in C++?

Question

I used to do it in high school but I haven't practised for a couple of years. What I'm trying to do is create an array which will store 100 IDs from 1-100. (This is for a game where each item will be assigned one of these IDs to distinguish each item from one another) This is my code,

#include <iostream>
#include <string>

using namespace std;

class items_class
{
public:
    items_class();
    ~items_class();
    static int item_ID[100];
};

items_class::items_class()
{
    for(int i=0;i<=100;i++)
        {
            item_ID[i] = i;
        }

}

int main()
{
    items_class items();

    for(int x=0;x<=100;x++)
        {
            cout << items.item_ID[x] << endl;
        }
}

but when I try to compile it I get this error:

main.cpp:29:27: error: request for member 'item_ID' in 'items', which is of non-class type 'items_class()' cout << items.item_ID[x] << endl;

Can anyone tell me why this is occurring? It's probably really obvious but I can't figure it out and I have scoured the internet all night! Grr.

Thanks in advance!

`items_class items();` -> `items_class items;` or `items_class items{};` — Piotr Skotnicki, Oct 01 '14 at 22:39
The somewhat vexing parse again...`items_class items();` declares a function called `items` taking no argument and returning an `item_class`. — T.C., Oct 01 '14 at 22:41
and also, statics must be defined, not only declared (but I guess you didn't want it to be static at all) — Piotr Skotnicki, Oct 01 '14 at 22:41
Why are you declaring the array as static? As a static variable, all classes that inherit from `items_class` will share the same instance of the variable. — Thomas Matthews, Oct 01 '14 at 22:46
@ThomasMatthews I think you mean that each *instance* of the class will share the variable (and you don't even need an instance to access it -- you have `items_class::item_ID` for that). — cdhowie, Oct 01 '14 at 22:48
@LukeDavidThompson: 0-based means that for array declared like `item_ID[100];` the first element is `item_ID[0]` and last item is `item_ID[99]`, but you are iterating up to `item_ID[100]` which is beyond the range — Piotr Skotnicki, Oct 01 '14 at 22:50
Oh yeah! I completely forgot about that, schoolboy error. derp also, I'm new to this site, so how do I upvote you? — Luke David Thompson, Oct 01 '14 at 22:51
@LukeDavidThompson: these are just comments, not answers, but no worries, noone posted answer as there are dozens of duplicates for your problem on SO — Piotr Skotnicki, Oct 01 '14 at 22:55
possible duplicate of [Default constructor with empty brackets](http://stackoverflow.com/questions/180172/default-constructor-with-empty-brackets) — HostileFork says dont trust SE, Oct 01 '14 at 23:17
Every time an items_class is constructed, the array is reinitialized. This is very inefficient. — Neil Kirk, Oct 02 '14 at 01:08

score 0 · Answer 1 · answered Oct 02 '14 at 00:39

Here's what you were missing, you declared your static variable but never defined it!

#include <iostream>
#include <string>

using namespace std;


class items_class
{
public:
    items_class();
    ~items_class();
    static int item_ID[100];
};

int items_class::item_ID[100]; // Need to define the static variable in a compilation unit.
items_class::items_class()
{
    for(int i=0;i<=100;i++)
        {
            items_class::item_ID[i] = i;
        }

}

int main()
{
    items_class items();

    for(int x=0;x<=100;x++)
        {
            cout << items_class::item_ID[x] << endl;
        }
}

score 0 · Answer 2 · answered Oct 02 '14 at 01:49

0

The previous answer assumed that the static variable is what you wanted. Another approach is to remove the static keyword. Then, when declaring items, remove the parens

answered Oct 02 '14 at 01:49

KC-NH

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How to call an array in the main function from a class in C++?

2 Answers2