How to make a function change a global array permanently

Question

Recently I've been working on an inventory system for a text-based game that uses a global array for the inventory system and a corresponding function to read true or false in said array. The problem I've run into is this, the function I'm using to modify the array

void playerGet(bool items[], int itemNumber) //this function takes an assigned argument of the array indices variable, and changes that array indices from true, to false. 
{
    items[itemNumber] = true;
}

only modifies the array within the scope of the function its housed in. The array is defined in a .cpp file like this:

void inventoryArray(bool items[]) //This function establishes all the items in the game, the true false statement expresses whether or not the item is in the player's inventory. 
{
    items[WEAPON_RELIC_RIFLE] = false;
    items[WEAPON_SCALPEL] = false;
    items[MISC_ACTION_FIGURE] = false;
    items[MISC_FIRE_EXTINGUISHER] = false;
    items[MISC_LIFE_RAFT] = false;
}

and is then declared in a .h file like this:

void inventoryArray(bool items[]);

the enums used in the array are defined in a header file like this:

enum equipment //This declares a list of enums for each item in the game, consumables, not included. 
{
    WEAPON_RELIC_RIFLE, // = 0
    WEAPON_SCALPEL, // = 1
    MISC_ACTION_FIGURE, // = 2
    MISC_FIRE_EXTINGUISHER, // = 3
    MISC_LIFE_RAFT, // = 4
    MAX_EQUIPMENT
};

the function that reads the inventory array is this:

void twoScavengerCombat(bool items[])
{
    for (int item = 0; item < MAX_EQUIPMENT; ++item)
    {
        if (items[item] == true) //if true proceed
        {
            switch (item)
            {
            case 0: //if array indices identifier = 0, print relic rifle
                cout << "1: Use the Relic Rifle\n";
                break;
            case 1:
                cout << "2: Use the Scalpel\n";
                break;
            case 2:
                break;
            case 3:
                cout << "3: Use the Fire Extingusher\n";
                break;
            case 4:
                cout << "4: Use the Life Raft\n";
                break;
            default:
                cout << "Error";
                break;
            }
        }
        else
            cout << "Option Unavailible\n"; //if false print Option Unavailible
    }

compiled, with the array and enums headers declared the main file would look like this:

int toolSearch()
{
   bool items[MAX_EQUIPMENT];
    inventoryArray(items);
   playerGet(items, 0);
}

void twoScavengerCombat(bool items[])\\ declared in this file, but since its just above here i left it as a forward declaration to save space

int main()
{
   toolSearch();
   twoScavengerCombat(items);
   return 0;
}

Ideally this would produce the result: Use Relic Rifle Option Unavailable Option Unavailable Option Unavailable Option Unavailable

but instead it produces 5 Option Unavailable's. What am I missing?

Answer 1

You would want

//bunch of #include<> directives
bool items[MAX_EQUIPMENT];

int toolSearch()
{
    inventoryArray();
    playerGet( 0);
}

void twoScavengerCombat()
...
// other functions here

int main()
{
   toolSearch();
   twoScavengerCombat();
   return 0;
}

Note that bool items[MAX_EQUIPMENT]; is not defined in a function. It is off on it's own at the top of the file in plain view of anything defined below it. This is what it means to be global. Anyone and everyone can access it, if they know where it is or you tell them where it is with an extern statement. It is created when the program starts (even before main and that can cause some really fun debugging if the initialization logic of the variable is faulty) and dies only when the program does.

Lightness Races in Orbit delves a bit deeper here, but is more concerned with making a global variable extend past a single file

There is no need to pass items into any function because everyone can see items The downside is there is one and only one items so if you have multiple players each with different item lists, you're going to have problems.

You might want to look into std::vector (resizable array) and std::map (which will allow you to look items up by name items["sword"].attackFoe(foe);) and std::set (which makes it really easy to see what a player has (if (items.find("Vorpal Hand Grenade") != items.end()) BlowStuffUp();) rather than having to search through each item every time.