What is wrong with my queue ADT?

Code:

---

#include "queue.h"

QUEUE* CreateQueue(void)
{
    QUEUE* queue;


    queue = (QUEUE*)malloc(sizeof(QUEUE));


    if(queue)
    {
        int count = 0;
        queue->front = NULL;
        queue->rear = NULL;
    }
    else
        return NULL;
    return queue;
}


bool Enqueue(QUEUE* queue, void* dataptr)
{
    NODE* newnode;
   
    if(!(newnode = (NODE*) malloc(sizeof(NODE))))
        return FALSE;


    newnode->dataptr = dataptr;
    newnode->next = NULL;


    if(queue->count == 0)
        queue->front = newnode;
    else
        queue->rear->next = newnode;
    (queue->count)++;
    queue->rear = newnode;
    return TRUE;
}


void* Dequeue (QUEUE* queue)
{
    void* dataOut;
    NODE* temp;
   
    if(queue->count == 0)
        return NULL;
    dataOut = queue->front->dataptr;
    temp = queue->front;
    queue->front = queue->front->next;
    if(queue->count == 1)
        queue->rear = NULL;
    (queue->count)--;
    free(temp);
    return dataOut;
}


void* QueueFront (QUEUE* queue)
{
    void* dataOut;
   
    if(queue->count == 0)
        return NULL;
    else
        return queue->front->dataptr;
}


void* QueueRear (QUEUE* queue)
{
    void* dataOut;
    if(queue->count == 0)
        return NULL;
    else
        return queue->rear->dataptr;
}


bool EmptyQueue (QUEUE* queue)
{
    return (queue->count == 0);
}   


bool FullQueue (QUEUE* queue)
{
    NODE* temp;


    temp = (NODE*)malloc(sizeof(*(queue->rear)));
    if(temp)
    {
        free(temp);
        return FALSE;
    }
    return TRUE;
}


int QueueCount(QUEUE* queue)
{
    return queue->count;
}


void DestroyQueue(QUEUE* queue)
{
    NODE* temp;
    if(queue->count != 0)
    {
        while(queue->front != NULL)
        {
            temp = queue->front;
            queue->front = queue->front->next;
            free(temp->dataptr);
            free(temp);
        }
    }
    free(queue);
}

---

So I tried to enqueue something very simple in main as so:

Code:

---

#include "queue.h"


int main(void)
{
    int* a;
    QUEUE* queue;


    queue = CreateQueue();
    a = (int*)malloc(sizeof(int));
    *a = 1;
    Enqueue(queue, a);
    return 0;
}

---

When I compile, the program crashes and my debugger states that there was an exception at this line:

Code:

---

bool Enqueue(QUEUE* queue, void* dataptr){
    NODE* newnode;
   
    if(!(newnode = (NODE*) malloc(sizeof(NODE))))
        return FALSE;


    newnode->dataptr = dataptr;
    newnode->next = NULL;


    if(queue->count == 0)
        queue->front = newnode;
    else
        queue->rear->next = newnode;
    (queue->count)++;
    queue->rear = newnode;
    return TRUE;
}

---

I am using Microsoft visual studio 2010.

Any help is appreciated!

Your code for queue.h is what?

Edit: A random guess of the problem; you forgot to include the header "stdlib.h".
http://faq.cprogramming.com/cgi-bin/...&id=1043284351

Quote:

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There is nothing wrong with this except in the event that stdlib.h, the header which declares malloc, is not included.

---

Tim S.

On line 13 you are not initialising queue->count, you are instead creating and not using a separate variable then goes out of scope shortly after.
Also, in main, everything is going okay and then you igmore your malloc'ed int and just pass in 5 directly. What's with that?

Code:

---

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


typedef struct node
{
    void* dataptr;
    struct node* next;
} NODE;


typedef struct queue
{
    int count;
    NODE* front;
    NODE* rear;
} QUEUE;


typedef enum {FALSE, TRUE} bool;


QUEUE* CreateQueue(void);
bool Enqueue(QUEUE* queue, void* dataptr);
void* Dequeue(QUEUE* queue);
void* QueueFront(QUEUE* queue);
void* QueueRear (QUEUE* queue);
bool EmptyQueue (QUEUE* queue);
bool FullQueue (QUEUE* queue);
int QueueCount (QUEUE* queue);
void DestroyQueue(QUEUE* queue);

---

that is my header file.

Quote:

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Also, in main, everything is going okay and then you igmore your malloc'ed int and just pass in 5 directly. What's with that?

---

typo, I fixed it

Quote:

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Originally Posted by iMalc

On line 13 you are not initialising queue->count, you are instead creating and not using a separate variable then goes out of scope shortly after.
Also, in main, everything is going okay and then you igmore your malloc'ed int and just pass in 5 directly. What's with that?

---

Did the problem go away after fixing "queue->count" initialization?
Note, if you did not fix it, why not?

Tim S.

Yes, the problem did go away after I fixed the initialization.
Appreciate the second pair of eyes to look over my dumb mistakes.

Thanks!