Got segmentation fault from code how to get rid of it?

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When I tried to debug this program it shows Program received signal SIGSEGV,Segmentation fault. I don't know what to do that's why I posted this question.

What I have tried:

C++

#include<stdio.h>
#include<conio.h>
#include<stdlib.h>
static int count=0;
struct node
{
	int coef;
	int pow;
	struct node *link;
};

struct node *head=NULL;

void showoff()
{
	struct node *t1;
	t1=head;
	while(t1!=NULL)
	{
		printf("|%d|%d|%x|--",t1->coef,t1->pow,t1->link);
		t1=t1->link;
	}
}

int main()
{
	int n,i=0;
	struct node *temp,*t;
	t=head;
	printf("Number of nodes\n");
	scanf("%d",&n);
	
	while(i<n)
	{
		temp=(struct node*)malloc(sizeof(struct node));
		temp->coef=NULL;
		temp->pow=NULL;
		
		if(count==0)
		{
			temp->link=head;
			head=temp;
		}
		if(count==1)
		{
			temp->link=head->link;
			head->link=temp;
		}
		if(count>1)
		{
			while(t->link!=NULL)    /*Responsible for error. Can you explain why*/
			{
				t=t->link;
			}
			temp->link=t->link;
			t->link=temp;
		}
		count++;
		i++;
	}
	showoff();
}

Posted 23-Aug-18 6:38am

Member 13954179

Updated 23-Aug-18 8:25am

Rick York

v2

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Rick York · Answer 1 · 2018-08-23T06:46:00

Solution 1

Firstly, you should use a debugger to fix this. It will show you quickly exactly what the problem is. If you do not have one with your compiler then get one that does. Visual Studio 2017 community edition is available at no cost ie., free.

My guess is the fault is caused because t is invalid and you are deferencing an invalid pointer.

Try adjusting your loop so you display things in every iteration :

C++

// ...
	for( i = 0; i < n; ++i )    // I prefer a for loop for this
	{
		// ... logic goes here

		printf( "i is %d, count is %d\n", i, count );
		showoff();
		count++;
	}

Posted 23-Aug-18 6:46am

Rick York

Updated 24-Aug-18 9:59am

v4

Comments

Member 13954179 23-Aug-18 12:58pm

Yeah I used debugger and it show that there is some problem with"while(t->link!=NULL)".
Error message "Program received signal SIGSEGV,Segmentation fault"

Member 13954179 23-Aug-18 13:07pm

So I got it that the problem is with t pointer, but now what. I literally don't what do it. I mean logically the program is right

Rick York 23-Aug-18 13:23pm

At this point you have to step through the program and watch everything it does so you can see where it becomes invalid. If that is a some time into its running then you might want to add trace or printf statements to display important information. This is one of the hardest things to learn about programming and that is debugging what you have written. Eventually you will learn techniques that help you write code that is easier to debug.

Rick York 23-Aug-18 13:28pm

You have the showoff function. I would move that so it displays things after each iteration so you can make you are correct with each one. Also display the counter while you are at it. These things well help you see what is happening better and that is the key to debugging : see what is going on with all of your data. I will adjust my first solution so you can see what I mean a little better.

Member 13954179 23-Aug-18 13:46pm

Thanks at last I got it

Rick York 23-Aug-18 13:52pm

What did you do to fix it?

Member 13954179 23-Aug-18 14:20pm

When condition arrives that count > 1, t remains NULL. As I set t = head at the beginning of main function, in for loop head is changed but t is not updated and it still contains NULL value, so I set t = head in scope for if (count>1). And problem solved. Thanks to everyone

raddevus · Answer 2 · 2018-08-23T07:49:00

Solution 2

Try breaking the following line into two lines:

C++

struct node *temp,*t;

Make it:

C++

struct node *temp;
struct node *t;

Just try that and rebuild and run see what happens.
I'm wondering if the struct * isn't being declared properly.

Posted 23-Aug-18 7:49am

raddevus

v2