Basic creating a queue crash

Question

Why does the program crash? Although sometimes it doesn't. I'm using visual studio 2017. I've run my entire program (more functions) with an online compiler and it doesn't crash. Thank you. [ Image of the crash2 1 []2

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

typedef struct Node {
    int data;
    struct Node* next;
}node;

typedef struct {
    int count;
    node *front;
    node *rear;
}QueueHead;

QueueHead *CreateQueue(){
    QueueHead *myQH = (QueueHead*)malloc(sizeof(myQH));
    //Empty list is created.
    //Emelent counter is set to zero
    myQH->count = 0;
    //Top should address NULL as it is an empty list
    myQH->front = NULL;
    myQH->rear = NULL;

    return myQH;
}

int main() {
    QueueHead *myQH = CreateQueue();
}

`myQH` is a pointer, so `malloc(sizeof(myQH))` is **not** enough memory for a `Queuehead` structure. — user3386109, Apr 17 '18 at 01:20
[Don't cast the result of malloc](https://stackoverflow.com/q/605845/119527). — Jonathon Reinhart, Apr 17 '18 at 10:58

score 0 · Answer 1 · answered Apr 17 '18 at 01:21

0

Try changing the line of code

QueueHead *myQH = (QueueHead*)malloc(sizeof(myQH));

to

QueueHead *myQH = (QueueHead*)malloc(sizeof(QueueHead));

answered Apr 17 '18 at 01:21

wookiekim

1,156
7
20

1

It worked! Thank you. – Nick Apr 17 '18 at 01:26
Better form would be `QueueHead *myQH = malloc(sizeof(*myQH));`. Don't cast the result of malloc, and don't repeat the type. – Jonathon Reinhart Apr 17 '18 at 10:59

Basic creating a queue crash

1 Answers1