Double **pointer question!

[pghTech]

Question regarding Double pointers.

It was told to me that if you passed a double pointer as an argument to a function :

int function1(type arg1, (type**) &arg2)
{
....
}

That you are passing the address to the pointer which, which is assumed is pointing to something else. And, that by doing so, you allow the function to point that double pointer to something else.

My question is, if it is a temporary storage of the address to the pointer that the function is receiving dictated no more than by (type**), how would you re-assign it to another address. Would you have to declare a new pointer in the function and assign it the (type**) address to it, then point it to something else?

And my last question (part II) is where does pointers really come into play and are helpful/useful?

Thanks much

[kuphryn]

arg2 = new type *[]

pointer is an invaluable asset to efficient, robust software architecture without sacrificing resources

Kuphryn

[wildfrog]

That you are passing the address to the pointer which, which is assumed is pointing to something else. And, that by doing so, you allow the function to point that double pointer to something else.

int	i = 5;
int j = 6;
int* pi = &i;

void func(int** ppi)
{
    // make pi point to j
    *ppi = &j;

    // change j to 10
    **ppi = 10;

    // chenge ppi. this only affects the local copy ppi
    ppi = 100;
}

int main()
{
    //pass double pointer (address of pi)
    func(&pi);
    return 0;
}

[ovidiucucu]

[ Moved thread ]

[humptydumpty]

here is a Small mistake in the Following Code

int	i = 5;
int j = 6;
int* pi = &i;

void func(int** ppi)
{
    // make pi point to j
    *ppi = &j;

    // change j to 10
    **ppi = 10;

    // chenge ppi. this only affects the local copy ppi
    ppi = 100;//And this Line contain Error too you are trying to convert const int to int** 
}

int main()
{
    //pass double pointer (address of pi)
    func(&pi);
    return 0;
}

Am i right Peter.

void func(int** ppi)
{
	// make pi point to i
	int my =25;
	int *my1 =&my;
	*ppi = &j; //assign 15 to ppi
	*ppi =&i;//change value to ppi
	ppi =&my1;//affect only upto local copy
	cout<<**ppi;//will print 25  here
	cout<<"\n";




}

int main()
{
	//pass double pointer (address of pi)
	int *pi;
	func(&pi);
	cout<<*pi;//here it will print 10
	return 0;
}

Thanx

[cilu]

here is a Small mistake in the Following Code

I didn't catch the mistake you are talking about...

[humptydumpty]

mention in bold letter

ppi=100;

and here is The line.

ppi = 100;//And this Line contain Error too you are trying to convert const int to int** 

Thanx

[cilu]

A, ok. Sorry, didn't pay attention to the comments.

[humptydumpty]

it's okay Cilu. Even that was a Minute mistake .
Thanx

[Vedam Shashank]

And my last question (part II) is where does pointers really come into play and are helpful/useful?

One....
Heart & soul of COM.... interfaces.
To obtain interface address from the component.

[humptydumpty]

That is.But i think when you want to perform calculation on Address of your data.that time you use pointers.

Thanx

[pghTech]

Thanks everyone for your reply's.

I made a mistake in my original post.

Instead of asking how "pointers" are helpful, I meant to ask

"How are DOUBLE pointers helpful", since they are already setup to be helpful in the sense that you can point to something else, or in the case of an array of pointers, easily change the sort easily.