Question

From what I understand, passing an entire structure to a function and not doing so by reference can be taxing on system resources. So, I’d like to get a handle on passing them by reference. I’m creating a character generator with the following structures:

struct Stats{
    string name;
    int level;
    int HP;
    int STR;
    int CON;
    int DEX;
    int INT;
    int WIS;
    int CHA;};

struct Growth{
    int HPperlvl;
    int STRperlvl;
    int CONperlvl;
    int DEXperlvl;
    int INTperlvl;
    int WISperlvl;
    int CHAperlvl;};

struct Holdstats{
    Stats classstats;
    Growth classgrowth;};
const int SIZE = 10;

Holdstats classlist[SIZE] = {
    { {"Fighter", 1, 18, 10, 10, 10, 10, 10, 10}, {1,1,1,1,1,1,1} },
    { {"Wizard", 1, 10, 10, 10, 10, 10, 10}, {1,1,1,1,1,1,1}},
    { {"Rogue", 1, 10, 10, 10, 10, 10, 10}, {1,1,1,1,1,1,1}}
} //These are just some examples, will be filled later

Holdstats charlist[SIZE]; //Empty array to store created characters

I’ll use the simplest function in the program to illustrate my problem. The following function is simply supposed to display info for whatever structure is passed to it, at whatever position in the structure is passed to it. The position is previously defined in the program. I would like to pass both the struct and the position by reference.

void dispinfo(const Holdstats &p, int &i) //Should be passed a position and a structure
{
    cout << endl << "\tHere is the Character/Class info you requested: "
        << "\n\t----------------------------------------------"
        << "\nName:\t\t" << p[i].classstats.name << endl
        << "Level:\t\t" << p[i].classstats.level << endl
        << "Hit Points:\t\t" << p[i].classstats.HP << endl
        << "Strength:\t\t" << p[i].classstats.STR << endl
        << "Constitution\t\t" << p[i].classstats.CON << endl
        << "Dexterity\t\t" << p[i].classstats.DEX << endl
        << "Intelligence\t\t" << p[i].classstats.INT << endl
        << "Wisdom\t\t" << p[i].classstats.WIS << endl
        << "Charisma\t\t" << p[i].classstats.CHA << endl;

}

The issue I’m getting has to do with p[i]. My compiler is telling me that for
Holdstats &p – no operator [] matches these operands. I would just use the name of a previously defined structure array (“classlist” or something) in the function header, but I want to be able to pass any array of structures to the function.

To my knowledge, I’m calling element i of a previously defined array. But obviously, I’m doing something wrong. Can anyone see the problem?

Answer 1

A few thoughts to try and help out.

• Unless you’ll be changing the value of i within dispinfo(), there’s really no reason to pass it by reference. Passing an int and passing a reference to an int is probably equivalent (both 32-bits more than likely) but then accessing that int by reference is (trivially) more taxing since it has to be dereferenced to get at the value.
• It looks like you’re expecting an array of Holdstats structs to get passed into dispinfo(). If that’s the case, you don’t need the reference symbol as arrays are always passed by reference. You should use Holdstats p[] instead of const Holdstats &p and the array would get passed in just fine (and you could compile). To call dispinfo() you’d just pass the array name and the index you want to print out.

You may want to consider changing dispinfo() to only receive a single Holdstats struct rather than an array of them. Then the function would look something like this.

void dispinfo(const Holdstats &p) //Should be passed a structure only
{
    cout << endl << "\tHere is the Character/Class info you requested: "
        << "\n\t----------------------------------------------"
        << "\nName:\t\t" << p.classstats.name << endl
        << "Level:\t\t" << p.classstats.level << endl
        << "Hit Points:\t\t" << p.classstats.HP << endl
        << "Strength:\t\t" << p.classstats.STR << endl
        << "Constitution\t\t" << p.classstats.CON << endl
        << "Dexterity\t\t" << p.classstats.DEX << endl
        << "Intelligence\t\t" << p.classstats.INT << endl
        << "Wisdom\t\t" << p.classstats.WIS << endl
        << "Charisma\t\t" << p.classstats.CHA << endl;

}

Then your call to dispinfo() would look something like this.

Holdstats classlist[SIZE] = { [...] };
dispinfo(classlist[0]);
dispinfo(classlist[1]);
[...]

That’s what you’d effectively be doing by passing the array and an index like so: dispinfo(classlist,0);