Using variables as part of a variable reference

Question

Pretty simple c++ question here, how do I replace part of variable reference with another variable, almost to concatenate it.

For example I have a structure with item1, item2, item3, I ask the user what Item they want the information of which is stored in a variable itemNo for example:

cout << "The item you selected is " << item(itemNo).name;

if itemNo==1 the reference would need to become item1.name;

Brackets is wrong in this scenario, but what is the right way to insert a number to form the right variable reference?

You can't do this, but you don't need to. Just use an array instead of 3 separate variables. — HolyBlackCat, Jan 24 '23 at 08:49
*Brackets is wrong in this scenario*, not if you overload `operator()`. But whether that is the right thing to do or not depends on the context (though it seems unlikely). Probably you need a vector or a map. — john, Jan 24 '23 at 08:55

score 1 · Answer 1 · answered Jan 24 '23 at 09:09

As mentioned in comments, if you name member item1,item2, item3,etc then you rather want a std::array, or if the number of items is dynamic then std::vector. Once you use a container as member, the container does provide a means of element access. However, as you are asking for it, it follows a way to make items(itemNo).name work. It makes use of operator overloading. And it uses a vector to store the data.

#include <string>
#include <vector>
#include <iostream>

struct Item { std::string name = "name";};
struct Items {
    std::vector<Item> data = std::vector<Item>(10);
    Item& operator()(size_t i) { return data[i];}
    const Item& operator()(size_t i) const { return data[i];}
};

int main() {
    Items items;
    items(5).name = "Hallo";
    std::cout << items(0).name << " " << items(5).name;
}

For further reading I refer you to operators@cppreference and What are the basic rules and idioms for operator overloading?. For the containers container@cppreference, std::array, and std::vector.

score -1 · Answer 2 · answered Jan 24 '23 at 09:16

You can define struct as a holder for your item

struct item {
   std::string name;
}

and then you can store items in array.

#include <array>
#include <string>
#include <iostream>

struct item {
   std::string name;
};

int main() {
  std::array<item, 3> items{ {{.name = "item1"}, {.name = "item2"}, {.name = "item3"}}};
  item& current_item = items[0];
  std::size_t  chosen{0};
  std::cout << "choose item (1-3):\n";
  std::cin >> chosen;
  current_item = items[chosen];

  std::cout <<  "current item: " << current_item.name << "\n";
}

You can switch to std::vector if you want to store dynamic number of elements.

Using variables as part of a variable reference

2 Answers2