Using std::find To Choose An Item From A Vector

Question

I am having an issue getting a vector-based inventory system to work. I am able to list the items in the inventory, but not able to allow a user-selected item to be accessed. Here is the code:

struct aItem
{
    string  itemName;
    int     damage;

    bool operator==(aItem other)
    {
        if (itemName == other.itemName)
            return true;
        else
            return false;
    }
};

int main()
{
    int selection = 0;


    aItem healingPotion;
    healingPotion.itemName = "Healing Potion";
    healingPotion.damage= 6;

    aItem fireballPotion;
    fireballPotion.itemName = "Potion of Fiery Balls";
    fireballPotion.damage = -2;

    aItem testPotion;
    testPotion.itemName = "I R NOT HERE";
    testPotion.damage = 9001;
    int choice = 0;
    vector<aItem> inventory;
    inventory.push_back(healingPotion);
    inventory.push_back(healingPotion);
    inventory.push_back(healingPotion);
    inventory.push_back(fireballPotion);

    cout << "This is a test game to use inventory items. Woo!" << endl;
    cout << "You're an injured fighter in a fight- real original, I know." << endl;
    cout << "1) Use an Item. 2) ...USE AN ITEM." << endl;

switch (selection)
    {
    case 1:
        cout << "Which item would you like to use?" << endl;
        int a = 1;
        for( vector<aItem>::size_type index = 0; index < inventory.size(); index++ ) 
        {

            cout << "Item " << a << ": " <<  inventory[index].itemName << endl;
            a+= 1;
        }
        cout << "MAKE YOUR CHOICE." << endl << "Choice: ";

        cin >> choice;

^^^^ Everything above this line, works. I assume that my problem is the if statement, but I cannot figure out where I am going wrong in my syntax, or if there is a better way to do what I am doing.

        if (find(inventory.begin(), inventory.at(choice), healingPotion.itemName) != inventory.end())
            cout << "You used a healing potion!";
        else
            cout << "FIERY BALLS OF JOY!";
        break;

    case 2:
        cout << "Such a jerk, you are." << endl;
            break;

    }

EDIT: I think I'm not representing this correctly. I need for the player's choice to affect the message displayed. Here's a sample output of the 1st snippet:

Item 1: Healing Potion
Item 2: Healing Potion
Item 3: Healing Potion
Item 4: Potion of Fiery Balls

MAKE YOUR CHOICE. 
Choice: 

From there, the player can type 1-4, and what I would like is for the number (minus 1, to reflect the vector starting at zero) to be passed to the find, which would then determine (in this small example) if the item at inventory[choice - 1] is a healing potion. If so, display "You used a healing potion!" and if it is not, to display "Fiery balls of joy".

Answer 1

Three problems.

One, Your operator should be declared as:

bool operator==(const aItem& other) const

Two, in this code:

find(inventory.begin(), inventory.at(choice), healingPotion) != inventory.end())

you aren't searching the whole vector from begin() to end() -- you're only searching from begin() to at(choice) where at(choice) points to one-past-the-end of your search set. So you either should do this:

find(&inventory.at(0), &inventory.at(choice), healingPotion) != &inventory.at(choice))

or this...

find(inventory.begin(), inventory.end(), healingPotion.itemName) != inventory.end())

Edit Three, you are trying to compare apples to oranges. You are searching a vector of aItem objects to find a matching aItem object, but the parameter you send to find isn't an aItem object, it is one of the aItem data members.

You should either search for a matching item, like this:

find( inventory.begin(), inventory.end(), healingPotion ) != inventory.end() )
                                            ^^^^^^^^

In C++03 you can provide a functor:

#include <functional>
struct match_name : public std::unary_function<aItem, bool>
{
    match_name(const string& test) : test_(test) {}
    bool operator()(const aItem& rhs) const
    {
        return rhs.itemName == test_;
    }
private:
  std::string test_;
};

... and then search for a match using find_if:

find_if( inventory.begin(), inventory.end(), match_name(healingPotion.itemName) ) // ...

In C++11 you can simplify this mess using a closure:

string test = healingPotion.itemName;
if( find_if( inventory.begin(), inventory.end(), [&test](const aItem& rhs)
{
    return test == rhs.itemName;
}) == inventory.end() )
{
  // not found
}

Answer 2

To add onto John Dibling's answer, the last part is that you are looking for a name, not an aItem.

So it either needs to be:

find(inventory.begin(), inventory.end(), healingPotion) != inventory.end();

where the operator== is defined as:

bool operator==(const aItem& other) const
{
   return itemName == other.itemName;
}

Or you need to have your operator== take a string:

find(inventory.begin(), inventory.end(), healingPotion.itemName) != inventory.end();

where the operator== is defined as:

bool operator==(const std::string& name) const
{
   return itemName == name;
}

Answer 3

Instead of:

case 1:
        cout << "Which item would you like to use?" << endl;
        int a = 1;
        for( vector<aItem>::size_type index = 0; index < inventory.size(); index++ ) 
        {

            cout << "Item " << a << ": " <<  inventory[index].itemName << endl;
            a+= 1;
        }
        cout << "MAKE YOUR CHOICE." << endl << "Choice: ";

        cin >> choice;
        if (find(inventory.begin(), inventory.at(choice), healingPotion.itemName) != inventory.end())
            cout << "You used a healing potion!";
        else
            cout << "FIERY BALLS OF JOY!";
        break;

    case 2:
        cout << "Such a jerk, you are." << endl;
            break;

    }

I neglected to realize that one of the wonders of vectors is the ability to access the value directly- Ryan Guthrie mentioned this in his comment, but I found a simpler "answer". Namely:

case 1:
    cout << "Which item would you like to use?" << endl;
    //TODO: Learn what the hell the following line actually means.
    for( vector<aItem>::size_type index = 0; index < inventory.size(); index++ ) 
    {
        //Makes a numerical list.
        cout << "Item " << index + 1 << ": " <<  inventory[index].itemName << endl;
        a+= 1;
    }
    cout << "MAKE YOUR CHOICE." << endl << "Choice: ";

    cin >> choice;
    //Cannot define this outside of the statement, or it'll initialize to -1
    invVecPos = (choice - 1);

    //This checks for an invalid response. TODO: Add in non-int checks. 
    if ((invVecPos) >= inventory.size())
    {
        cout << "Choice out of bounds. Stop being a dick." << endl;
    }
    //If the choice is valid, proceed.
    else
    {
        //checking for a certain item type.
        if(inventory[invVecPos].itemType == "ITEM_HEALTHPOT")
        {
            cout << "You used a healing potion!" << endl;
            //this erases the potion, and automagically moves everything up a tick.
            inventory.erase (inventory.begin() + (invVecPos));
        }

        else if(inventory[invVecPos].itemType == "ITEM_FIREPOT")
        {
            cout << "FIERY BALLS OF JOY!" << endl;
        }

        else
        {
            //error-handling! Whee!
            cout << "Invalid Item type" << endl;
        }
    }


    break;
case 2:
    cout << "Why do you have to be so difficult? Pick 1!" << endl;
    break;

Thank you, Ryan- with your prodding, I was able to look elsewhere and find the code I needed! The "fixed" code is commented heavily, so anyone else who runs into issues should be able to glean what they need!