2D Dynamically allocated pointer arrays

**Lionmane** · 06-10-2005

I figured out what that memory issue was. I was trying to use the free function (see my previous code post).

When I REM out the free function, the code works without any errors!?

I've had problems with the free function before; does anyone know what I'm doing wrong?

mw

**quzah** · 06-10-2005

Probably freeing something you shouldn't. Like Salem said, post your code.

Quzah.

**Lionmane** · 06-10-2005

My code hasn't changed since the previous posting. Did you still want me to post it?

mw

**quzah** · 06-10-2005

I suppose that's up to you. If you still think calling free is what's breaking your program. Personally I don't care if you find out the answer and how to program or not. But if you do, then you might want to post it. It's up to you.

Quzah.

**Lionmane** · 06-10-2005

You're pretty rude.

Code:

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

/*

This program demonstrates recursive functions and dynamic, multi-dimensional pointer arrays.

It will calculate the total factorial value for multiple groups of items.

You enter the total number of items, and the number of groups you will have.  Then you enter the
number of items in each group.  The program error-checks to make sure the number of items
entered in each groups adds up to be the total number of items.

*/


//	Prototypes.

unsigned long factr (unsigned long num_items2, unsigned long num_groups2);
unsigned long factorial_engine (unsigned long n);

void main ()
{
	unsigned long num_items = 0;
	unsigned long num_groups = 0;

	printf ("\n\nHow many items total?\n");
	scanf ("%u", &num_items);

	printf ("\n\nHow many groups?\n");
	scanf ("%u", &num_groups);

	if (num_groups > num_items)
	{
		printf("\n\nError! Can't have more groups than items!\n\n");
		exit (1);
	}
	else
	{
		factr (num_items, num_groups);
	}
}

unsigned long factr (unsigned long num_items2, unsigned long num_groups2)
{

//	These are in order of appearance.

	unsigned long loop = 0;
	unsigned long total = 0;
	unsigned long quantity = 0;
	unsigned long numerator = 0;
	unsigned long denominator = 1;

//	Array dimensioning.

	unsigned long *group_total;
	group_total = malloc (num_groups2*2*sizeof(int));

	if(!group_total)
	{
		puts ("\n\nERROR! Not enough Memory!\n\n");
		exit (1);
	}

//	Array initialization.

	for (loop = 1; loop <= num_items2; loop++)
	{
		group_total[loop][1] = 0;
		group_total[loop][2] = 0;
	}
	loop = 0;

//	Array data-entry.

	for (loop = 1; loop <= num_groups2; loop++)
	{
		printf ("\n\nHow many in group %d\n", loop);
		scanf ("%u", &quantity);

		group_total[loop][1] = quantity;
		total = total + quantity;
	}
	loop = 0;

//	Error checking and factorial calculations for each group

	if (total = num_groups2);
	{
		for (loop = 1; loop <= num_groups2; loop++)
		{
			group_total[loop][2] = factr (quantity);
		}
		loop = 0;
	}
	else
	{
		printf ("\n\nTotal number of items not equal to total items entered!\n\n");
		free (group_total);
		exit (1);
	}
	total = 0;

//	Final calculations.

	numerator = factr (num_items2);

	for (loop = 1; loop <= num_groups2; loop++)
	{
		denominator = denominator * group_total[loop][2];
	}
	total = numerator / denominator;
	printf ("\n\nTotal factorial for this mess: %u\n\n", total);
	total = 0;
	loop = 0;
	free (group_total);
}

//	Factorial engine.

unsigned long factorial_engine (unsigned long n)
{
	unsigned long answer;

	if (n==1) return (1);
	answer = n==0 ? 1: n * factr (n - 1); // recursive call
	return (answer);
}

**Lionmane** · 06-10-2005

So you're not going to help me now? I asked if it were alright to post my code again because I didn't want to post it too many times. Your answer was childish.

If you don't like me saying that then tough. Grow up.

mw

**quzah** · 06-10-2005

So you don't post code here when originally asked, and then you expect me to hang around for the rest of my life hoping you actually post it? Is that it? I'm sorry, there were a few other things I felt like doing, rather than hoping you'd get around to listening to people.

What's that? I shouldn't have read and replied to any one else's posts and just answered yours, in the off chance you actually posted your code? Yeah. I'm the rude one.

Quzah.

**Lionmane** · 06-10-2005

So are you going to help me?

mw

**quzah** · 06-10-2005

Well let's begin, shall we?

1) This is wrong. Read the FAQ.

Code:

void main ()

2) This is wrong. Arrays do not start at 1. They start at 0. Also, they do not go through "size", they go through "size - 1".

Code:

//	Array initialization.

	for (loop = 1; loop <= num_items2; loop++)
	{
		group_total[loop][1] = 0;
		group_total[loop][2] = 0;
	}
	loop = 0;

Also, there's absolutely no point in setting loop to 0 at the end. Furthermore, what exactly do you think you're doing with the second set of array indexes? Nothing correct, that's for sure. Just because you decide to add more array indexes, doesn't mean it's going to magicly move down to your second array dimension, because there isn't one.

I mean really, you don't even understand the simplest things:

3) This is an assignment, not a truth test:

Code:

	if (total = num_groups2);

This says "assign the value in num_groups2 to total", and then as long as that assignment's value is non-zero, considers itself true.

In short, free is not your problem. The problem is you don't have a clue as to what you're doing, even though you've been shown over and over how to do it right.

Quzah.

**Lionmane** · 06-10-2005

Ok, I've corrected those issues. My program compiles correctly and I've tested it enough to know that it works correctly when I test it.

Honestly, all I did was copy/paste my program from the previous page. I corrected those issues that you mentioned earlier this afternoon, but the code was still essentially the same.

Now when I try to use the free function I get that error.

mw

**Thantos** · 06-10-2005

Originally Posted by Lionmane

You're pretty rude.

Don't confuse rudeness with blunt honesty

**Lionmane** · 06-10-2005

When your signature is "Hello. You're an idiot", then it's pretty safe to assume the whole attitude is wrong.

Also, there's very little difference between "blunt" and "rude".

Try acting the way he does when you're around women and see how often you get laid (blunt honesty).

mw

**quzah** · 06-10-2005

Originally Posted by Lionmane

Ok, I've corrected those issues.

I doubt it. I really doubt you've "corrected those issues", since I bet you don't even know what specificly I was talking about with your incorrect array indexing. (No, not the loop initializer, the subscripting.)

Quzah.

**Lionmane** · 06-10-2005

The declaration:
int array(10);

means:
array(0)
array(1)
array(2)
array(3)
etc...
array(9)

It was easy enough to change, and easy enough to understand.

Look, if you don't know how to use the free function then why are you posting?

Oh yeah: I read the FAQ about void main() and I'll correct it as soon as I get to my work computer.

mw

**quzah** · 06-10-2005

The free call is not your problem. I've already said that. You're just being an idiot and ignoring me again. The problem is you don't know how to use your dynamic memory correctly, and you're traipsing around in memory where you don't belong. Still don't believe me? Here, let me show you:

Code:

#include <stdlib.h>

int main( void )
{
    unsigned long num_groups2 = 10;
    unsigned long *group_total;
    group_total = malloc (num_groups2*2*sizeof(int));    

    free( group_total );

    return 0;
}

Compile that, run it. Does it crash? No. It doesn't. That means free is not your problem. Holy deja vu, Batman!

Quzah.