Array of structs

I am making this MUD-type game and each player struct has two other structs called "gear" and "inventory"

Gear is what is worn, and that is an array of item-structs (item_t item[11], it is typedef'd)
Inventory is the same but with a size of 20 instead of 11.

When I want to load a character, I access the "item ID" from a file (a regular integer) and pass it to a function that should return the correct item, so that it can be applied to the correct inventory/gear slot before the game starts. My problem is that the program crashes as soon as I try to fill these inventory/gear slots... It reads all attributes and strings from the save-file perfectly, so I have narrowed it down to being a definition error (I just started using structs and C)

This is the stuff:

Code:

---

typedef struct item_s {
  ... all kinds of normal data types
} item_t;

typedef struct inventory_s {
  item_t* item[20];
} inventory_t;

typedef struct gear_s {
  item_t* item[MAX_SLOTS]; //#define MAX_SLOTS 11
} gear_t

---

Then when I try to initialize these, I do this:

Code:

---

if(pos == 13) p->backpack.item[pos-13] = get_item(atoi(buf));

---

p is a pointer to a player struct and backpack is an inventory-struct.

And I do this for every slot. buf is not wrong, that I am certain of.

Here's get_item(int id):

Code:

---

item_t* get_item(int id) {
  item_t *t;
  strcpy(t->name, "empty");
  return t;
}

---

I havent implemented the ID-thing yet so it just returns an item called "empty".

Need help badly :|

This was much easier with classes and "new ()".

Code:

---

item_t* get_item(int id) {
  item_t *t;
  strcpy(t->name, "empty");
  return t;
}

---

What does t point to here?





(Glances at clock)







The answer is that it points anywhere! So you're trying to write a string to a pointer of a struct that can't be dereferenced because it's invalid. BOOM.

Looking at what struct info you've provided, you've got issues. A lot of the time you've declared item_t * instead of item_t. What this means is instead of an array of e.g. 20 item_t's, you've got an array of 20 pointers to item_t's. You would have to allocate memory using malloc() for each one as you go to use them and free() afterwards. I don't think that at this stage you want to do that.

So... drop the asterisks from your item_t declarations in your structs. Also rewrite get_item() like so:-

Code:

---

void get_item(t_item *t, int id) {
  strcpy(t->name, "empty");
}

---

And call like "get_item(p->backpack.item[pos-13], atoi(buf));"
Rinse and repeat.

This is where u'r code goes wrong

Code:

---

item_t* get_item(int id) {
  item_t *t;
  strcpy(t->name, "empty");
  return t;
}

---

u havn't allocated space for it. either u can use a malloc. Or use that malloc in a fucntion and call the function which return the address of the allocated space.

Code:

---

item_t* AllocateSpace(void)
{
    return malloc(sizeof(item_t) * 1);
}

---

And call this function here

Code:

---

item_t *t = AllocateSpace();

---

But either SMurf solution would better cos. it reduces complication. You will need this sort of allocation struct when use Linkes structure and many others.

ssharish2005

Your get_item()-function passes an item_t, not a pointer to one.

Doesn't work :F

thats the mistake which u have done. u hanv't allocated space for item_t *. use malloc to do that and then return the pointer back. See mypost. Or look at the SMurf solution.

ssharish2005

I'm feeling charitable today, so here's a complete working listing for you, based on what you've provided.

Code:

---

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#define MAX_SLOTS 11

typedef struct item_s {
    // let's go with what we know
    char name[40];
} item_t;

typedef struct inventory_s {
  item_t item[20];
} inventory_t;

typedef struct gear_s {
  item_t item[MAX_SLOTS];
} gear_t;

typedef struct player_s {
    // amongst other things...
    inventory_t backpack;
} player_t;

void get_item(item_t *t, int id) {
  strcpy(t->name, "empty");
}

int main(void)
{
    char buf[10] = "69";
    int pos = 13;
    player_t *p;

    p = malloc(sizeof(*p));
    if (pos == 13)
        get_item(&p->backpack.item[pos-13], atoi(buf));

    printf("Item in backpack at index (pos - 13) is: %s\n", p->backpack.item[pos-13].name);
    free(p);
    return 0;
}

---

A quite basic example, but it does illustrate what I wrote earlier. Note that I call malloc() in order to allocate memory for the player pointer and free() it when I am completely finished with it. Have a play with that.