A queue in C using structs and dynamic memory allocation (linked list)
- by Martin Pugh
I am tasked with making a queue data structure in C, as a linked list. Our lecturer gave us a large amount of code to implement a stack, but we have to adapt it to create a queue. The code our lecturer gave us ends up not compiling and segfaulting at the exact same point as the code I wrote for the queue. I'm very new to structs, malloc and C in general, so there could be something painfully obvious I've overlooked.
Here is the code I am using:
#include <stdio.h>
#include <stdlib.h>
struct node{
int data; //contains the actual data
struct node *prev; //pointer to previous node (Closer to front)
struct node *next; //pointer to next node (Closer to back)
};
typedef struct node *Nodepointer;
struct queue{
Nodepointer front;
Nodepointer back;
};
typedef struct queue *Queuepointer;
main(){
Queuepointer myqueue; //create a queue called myqueue
init(myqueue); //initialise the queue
Nodepointer new = (Nodepointer)malloc(sizeof(struct node));
myqueue->front = new;
}
int init(Queuepointer q){
q = (Queuepointer)malloc(sizeof(struct queue));
q->front = NULL;
q->back = NULL;
}
The idea is that the queue struct 'contains' the first and last nodes in a queue, and when a node is created, myqueue is updated. However, I cannot even get to that part (pop and push are written but omitted for brevity). The code is segfaulting at the line
myqueue->front = new;
with the following gdb output:
Program received signal SIGSEGV, Segmentation fault.
0x08048401 in main () at queue.c:27
27 myqueue->front = new;
Any idea what I'm doing wrong?
