"no matching function for call to" function call on object - c++

Question

I am having an issue where every spot where I make a function call, such as item.GetName(), on an item in the vector<ItemToPurchase> items , I get the error message: no matching function for call to vector<ItemToPurchase,__default_alloc_template<false,0> >::at (int &) I've been looking all over and don't even uderstand what the "no matching function for call to" even means.
Example g++ message
ShoppingCart.cpp: In method `bool ShoppingCart::CheckCartForItem(class
string)':
ShoppingCart.cpp:22: no matching function for call to
`vector<ItemToPurchase,__default_alloc_template<false,0> >::at (int &)'
ShoppingCart.h:
#ifndef SHOPPINGCART_H
#define SHOPPINGCART_H
#include "ItemToPurchase.h"
#include <vector>
class ShoppingCart
{
public:
ShoppingCart(string customerName = "none", string dateCreated = "January 1, 2016");
*other functions*
bool CheckCartForItem(string itemName);
void AddItemToCart(ItemToPurchase item);
*more functions*
private:
*other variables*
std::vector<ItemToPurchase> items;
};
#endif
ShoppingCart.cpp
#include "ShoppingCart.h"
#include <iostream>
ShoppingCart::ShoppingCart(string customerName, string dateCreated)
{
this->customerName = customerName;
this->dateCreated = dateCreated;
}
bool ShoppingCart::CheckCartForItem(string itemName)
{
if (items.size() == 0) //if cart is empty
return false;
for (int i = 0; i < items.size(); i++)
{
if (items.at(i).GetName() == itemName) //<- Problem here
return true;
}
return false;
}
void ShoppingCart::AddItemToCart(ItemToPurchase item)
{
if (CheckCartForItem(item.GetName()) == false) //if item not in cart
items.push_back(item);
else
cout << "Item is already in cart. Nothing added." << endl;
}
ItemToPurchase.h
#ifndef ITEMTOPURCHASE_H
#define ITEMTOPURCHASE_H
#include <string>
using namespace std;
class ItemToPurchase
{
public:
ItemToPurchase(string name = "none", string description = "none", double
price = 0.0, int quantity = 0);
void SetName(string);
string GetName();
*other functions*
private:
string itemName;
*other variables*
};
#endif // ITEMTOPURCHASE_H
ItemToPurchase.cpp
#include "ItemToPurchase.h"
#include <iostream>
#include <iomanip>
ItemToPurchase::ItemToPurchase(string name, string description, double
price, int quantity)
{
itemName = name;
itemDescription = description;
itemPrice = price;
itemQuantity = quantity;
}
void ItemToPurchase::SetName(string name){ itemName = name; }
string ItemToPurchase::GetName() { return itemName; }

Answer 1

Since in this case you don't use the index variable, you can iterate with a range-based for loop:
for (auto& item : items) {
if (item.GetName() == itemName) {
[...]
std::vector:at expects a std::vector::size_type (which is typically defined as std::size_t). Changing the type of i should make it compatible when using the index-based accessor:
for (std::vector<ItemToPurchase>::size_type i = 0; i < items.size(); ++i) {
if (items.at(i).GetName() == itemName) {
[...]