How would I make a flexible struct inside another struct?

May 5, 2024

I’m trying to create an item and box system, where a box can have a flexible amount of items inside it (i.e. not wasting memory by making every box have 50 items, when some will have just a few). I am not quite sure how to do it.

I tried to put the Item struct inside the Box struct as a flexible array, but it doesn’t really work.

Here’s my code:

struct Item {
    char name[64];
    char slot;
    int weight;
    int size;
    int dmg;
};

struct Box {
    int size;
    Item items[size];
};

int main()
{
    Item sword = { "Sword", 'W', 20, 8, 5};
    Box box = { 3, (sword, sword, sword) };
}

>Solution :

A possible solution would be to use std::vector as a dynamic-size container.

You should also use std::string for strings like name (instead of a plain char array). Among other advatages, it will remove the limit of name length of 63 characters you have now.

A minimal example initializing a box with 3 items and then adding 1 item is demonstrated below:

#include <string>
#include <vector>

struct Item {
    std::string name;
    char slot;
    int weight;
    int size;
    int dmg;
};

struct Box {
    std::vector<Item> items;
};

int main()
{
    Item sword = { "Sword", 'W', 20, 8, 5 };
    Box box;
    box.items = { sword, sword, sword }; // initialize with 3 items
    box.items.push_back(sword);          // add another item
}

Notes:

Consider to encapsulate the data fields by making them private and providing accessor methods.
Consider to add constructors for Item and Box, and possibly other methods like add_item for Box.