Adding a new node to linkded list

[OCcounty]

Hi there. I am trying to add a node to linked list using function append(). It is giving me SegementViolation error at the highlighted lines. Does anybody have any clue as to what is wrong?

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

struct node
{
	int  data;
	struct node *link;
};

int main(int argc, char **argv)
{
	struct node *p;
	int num;
	p= (struct node *)malloc(sizeof(struct node));
	if(p->link != NULL)
	{
		p= p->link;
	}
	
	printf("\n Enter num:");
	scanf("%d", &num);
	
	append(p,num);
	
	printf("\n hello world\n");
	return 0;
}


append(struct node **q, int num)
{
	struct node *temp,*r;
	printf("\n in append");
	
	r = *q;
	
	temp = (struct node *)malloc(sizeof(struct node));
	temp->data = num;
	temp->link = NULL;
	r->link = temp;
	
	//Display linked list elements 
	temp = *q;
		printf("\n Before while");
		while(temp->link != NULL)
	 {
		  printf("%d",temp->data);
		 temp = temp->link;
	 }
	 
}

[Bayint Naung]

append(p,num); // p is declared as pointer to node
VS
append(struct node **q, int num);

It's a bad habit to ignore compiler warnings.

[OCcounty]

In above snippet, I am receiving signal SIGSEGV at lines:
1. append(p,num);
2. r = *q;

[OCcounty]

I did not understand. Can you explain in details ? Please.

[cyberfish]

What does the compiler tell you when you compile this code?

[OCcounty]

I did not understand. Can you explain in details ? Please.

[OCcounty]

Compiler gives the error"Program Received signal SIGSEGV".

[cyberfish]

That's not the compiler. That's when you run it.

append() takes a double pointer to node. You are passing in a single pointer to node. The compiler should have warned you about this.

Also, append() is declared without a return type, that is bad.

[OCcounty]

No compiler gives 0 errors and 0 warnings. It is during the run I encounter this error.
I stated the return type for append() and after that I do not receive any SIGSEGV error. Now the output screens do scan for the num but do not display the final output.
Thank you for your help.

[quzah]

If you aren't getting warnings then you aren't compiling with warnings enabled. At a bare minimum, your original code will complain that you are passing it the incorrect type to append.


Quzah.

[OCcounty]

I do get warnings but I am not getting any of them now!!

[68656c70]

Maybe this will help you:

append(struct node *q, int num)
{
     struct node *temp;
     printf("\n in append");
     temp = (struct node *)malloc(sizeof(struct node));
     temp->data = num;
     temp->link = NULL;
     q->link = temp;
     temp = q;
     printf("\n Before while");
     while(temp->link != NULL)
     {
          printf("%d",temp->data);
          temp = temp->link;
     }
}

For me, it prints zero after "Before while" because num is stored in a new node instead of current node.
It doesn't print the inserted number because new node's link points to NULL.

[Elysia]

You're still missing a fact: append lacks a return type. And you are not returning anything.

[68656c70]

Could be void... it isn't that significant at this point. I concentrated on logical errors rather than syntactical errors. Gcc didn't throw any errors/warnings though.

[Elysia]

But it isn't void.
You need to tell it to be strict. Compile with C99, all warnings and pedantic.