(int *) variable

[Bilbo]

Hello everybody.

What does an (int *) type of variable mean?

Thanks

Derek

[Sam Jervis]

Re: (int *) variable

Bilbo wrote:[color=blue]
> Hello everybody.
>
> What does an (int *) type of variable mean?
>
> Thanks
>
> Derek
>[/color]

It is a pointer to an int i.e. the variable stores the memory location
of an int rather than the actual int itself.

You use (int *) like this:

int a;
int *p;

a = 42;
p = &a; /* p now contains the memory location of a */
*p = 21; /* a now contains the value 21 */

So you use & to get the address of a variable, and you use * in the
context *p to dereference the pointer i.e. to get at the value it is
pointing to.

Hope this helps,
Sam

[Malcolm]

Re: (int *) variable


"Sam Jervis" <sam@heffalump. me.uk> wrote in message[color=blue]
>
> You use (int *) like this:
>
> int a;
> int *p;
>
> a = 42;
> p = &a; /* p now contains the memory location of a */
> *p = 21; /* a now contains the value 21 */
>[/color]
This is correct but maybe leaves the OP wondering "what is the point of
that?".

One answer is that a C function can return only one value. If we want a
function "getcursorp os" we need to return both x and y.

we do it like this.

/* globals maintained by the cursor handling routines */
int g_cursorxpos;
int g_cursorypos;

void getcursorpos(in t *x, int *y)
{
*x = g_cursorxpos;
*y = g_cursorypos;
}

void callingfunction (void)
{
int cx;
int cy;

getcursorpos(&c x, &cy);
printf("The cursor is at position %d %d\n", cx, cy);
}


The most common use however is to pass an array of integers to another
function. For instance if we want to calculate the mean of a list of numbers
we would write

int mean(int *array, int N)

However the details of pointer and arrays are maybe best left until you've
got the idea of storing addresses in pointers.