CODEWITHSUNDEEP
linuxdata-structuresqueueruntime-error
user3409814
user3409814

Reputation: 245

Implementation of Queue giving runtime error

I wrote this program to build a queue.

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

typedef struct Queue{
    int *array;
    int front,rear,size,capacity;
}Queue;

int isFull(Queue *q){
    return q->size == q->capacity;
}

int isEmpty(Queue *q){
    return q->size == 0;
}

Queue *createQueue(int capacity){
    Queue *q = (Queue *)malloc(sizeof(Queue));
    q->size = 0;
    q->front = 0;
    q->capacity = capacity;
    q->rear = capacity - 1;
    q->array = (int *)malloc(sizeof(int)*capacity);
}

void enqueue(Queue *q,int num){
    if(isFull(q))
        return;
    q->rear = (q->rear + 1) % q->capacity;
    q->array[q->rear] = num;
    q->size++;
}

int dequeue(Queue *q){
    int item;
    if(isEmpty(q))
        return -1;
    item = q->array[q->front];
    q->front = (q->front + 1) % q->capacity;
    q->size--;
    return item;
}

int main(void) {
    Queue *q = createQueue(10);

    enqueue(q,1);
    enqueue(q,2);
    enqueue(q,3);
    enqueue(q,4);

    printf("%d ",dequeue(q));
    printf("%d ",dequeue(q));
    printf("%d ",dequeue(q));
    printf("%d ",dequeue(q));

    return 0;
}

Program works perfectly fine when run from Linux terminal. When I run the same program in ideone.com I am getting a runtime error.

I did try to find memory leaks in the program manually. There seems to be no problem

Why is this happening?

Upvotes: 0

Views: 166

Answers (2)

Ayush
Ayush

Reputation: 2608

Queue *createQueue(int capacity){
    Queue *q = (Queue *)malloc(sizeof(Queue));
    q->size = 0;
    q->front = 0;
    q->capacity = capacity;
    q->rear = capacity - 1;
    q->array = (int *)malloc(sizeof(int)*capacity);
    return q;
}

Upvotes: 0

PW.
PW.

Reputation: 3725

Your function createQueue is supposed to return a pointer to a Queue but there's no explicit return in it: what is returned by your function is not guaranted across compiler/platforms.

This type of error is catched by gcc with warnings turned on (-Wall).

Upvotes: 1

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