CODEWITHSUNDEEP
c
Ron
Ron

Reputation: 11

Initializing a struct array inside a struct

I've looked at other questions but I can't seem to find a clear answer for this. How do I declare a struct array inside of a struct? I attempted to do it in main() but I don't know if I'm doing it right and I keep getting this warning: "initialization makes integer from a pointer without cast"

#define MAXCARDS 20     

struct card {
    int priority;       
};

struct battleQ {
    struct card cards[MAXCARDS];
    int head;
    int tail;
    int size;
};

int main (int argc, char *argv[]) {
    struct battleQ bq;
    bq.cards = {
                      malloc(MAXCARDS * sizeof (struct card)), //Trouble with this part
                      0,
                      0,
                      0
                };

        //...

    return 1;
}

Edit after suggestions: Okay now I'm having problems. I keep getting this error: 

3 [main] TurnBasedSystem 47792 open_stackdumpfile: Dumping stack trace to TurnBasedSystem.exe.stackdump

I had to change the code a bit and make everything pointers. I tested it and it gives me that error as soon as I try to assign one of its attributes like: bq->head = 0

The entire thing is just supposed to add a card to a queue. Revised code is below:

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

#define MAXCARDS 20

struct card {
    int priority;       
};

// A queue defined by a circular array
struct battleQ {
    struct card *cards[MAXCARDS];
    int head;
    int tail;
    int size;
};

bool battleQEnqueue (struct battleQ *bq, struct card *c);
bool battleQisFull(struct battleQ *bq);

// Method for enqueuing a card to the queue
bool battleQEnqueue (struct battleQ *bq, struct card *c) {
    bool success = false;
    if (battleQisFull(&bq)) {
        printf("Error: Battle queue is full\n");
    } else {
        success = true;
        bq->cards[bq->tail] = c;
        bq->size = bq->size + 1;
        bq->tail = (bq->tail + 1) % MAXCARDS;
    }
    return success;
}

int main (int argc, char *argv[]) {
    int i;
    struct battleQ *bq;
    memset(&bq, 0, sizeof(bq));  // Did I do this properly?
    bq->tail = 0;               // Gives error at this point
    bq->head = 0;               
    bq->size = 0;

    // This is where I create a card and add it to the queue but the main problem
    // is still the initialization above
    for (i = 0; i < 5; i++) {
        struct card *c = malloc(sizeof(c));
        c->priority = i + 10;
        printf("%d,", c->priority);
        battleQEnqueue(&bq, &c);
    }

    return 1;
}

Upvotes: 1

Views: 6265

Answers (3)

alk
alk

Reputation: 70883

You might like to initialise the whole structure this way:

...

int main(int argc, char *argv[])
{
  struct battleQ bq =
  {
    {
      { 0 } /* int priority; */
    } /* (initialising the first element/member initialises all element/member) */
  }; 

  //...

  return 1;
}

Upvotes: 1

Rohan
Rohan

Reputation: 53316

bq.cards is array of structs, you don't have to malloc it. You can initialize the entire array as:

memset(bq.cards, 0, sizeof(bq.cards));

If you want to initialize bq do

    memset(&bq, 0, sizeof(bq));

Upvotes: 3

cup
cup

Reputation: 8237

The initialization is in the declaration

struct battleQ bq = {
              {{0}, {0},... // 20 times
              },
                  0,
                  0,
                  0
            };

It might be better to have cards as the last element, then you can use a trick called the chumminess of C. http://c-faq.com/struct/structhack.html, where you can have a variable sized battleQ.

I may be wrong on this but what I've found on most compilers is that if you set the first element to zero, everything else will be zero. I remember reading something in the standard about it but I can't remember were or whether it was C or C++.

struct battleQ bq = {{{0}}};

Upvotes: 0

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