How can pointers be used in VB?

[Michael]

Hello,

How can pointers be used in VB?
Here is an example in 'C'
How can the same be done in VB?

(I am using MS Access 2000)

Thanks,

Michael


Code: -------------------------------------


typedef far struct point {
float x;
float y;
float z;
float d;
struct point far *nextX;
struct point far *nextY;
} far Point;


void main(void)
{
float a,b,c;
Point far *p2D;

/*... code ...*/

CalculPts(a,b,c,&p2D);

} /* main */



void CalculPts(float aa, float bb, float cc, Point far
**pt2D)
{
Point far *currentX,far *currentY;


*pt2D = (Point far *) farmalloc(sizeof(Point));
currentX = *pt2D;
currentY = *pt2D;

currentX->x = aa;
currentX->y = bb;
currentX->z = cc;
currentX->d = 1;

/*... code ...*/

currentX->nextX=NULL;
currentX->nextY = currentY;

/*... code ...*/

if (currentX->nextX!=NULL) currentX = currentX->nextX;

/*... code ...*/

currentY->nextY = (Point far *) farmalloc(sizeof
(Point));
if (currentY!=NULL) currentY = currentY->nextY;

} /* CalculPts */

 

[Dan Artuso]

Hi,
If I'm understanding your code correctly you could probably
do the same thing using classes (instead of structs which in vb are types).

If you google on "visual basic" linked lists -.net
you should get some results

Here is one that starts right from scratch:
http://www.mvps.org/vb/hardcore/html/collectingobjects.htm

 

[Albert D. Kallal]

No, VB does not have pointers. You can pass vars to a function or sub as "by
ref" as opposed to "by value"

So, using by "ref" means that only a pointer to the variable in memory is
passed. This of course is faster, as a "copy" of the value is not made.

Any values passed to the sub/function, and then changed in that sub/function
will thus be returned/changed to the calling routine.

However, returning a values is certainly not a "pointer" data type, and thus
making a "linked" list as you have is not very easy in VB.

To create a dynamic structure in VB that has "N" values, likely a collection
is a good deal better then resorting to a array. The only draw back of a
collection is that each element of the collection can't be modified in the
collection (you would have to remove it first).

 

[Tim Ferguson]

However, returning a values is certainly not a "pointer" data type,
and thus making a "linked" list as you have is not very easy in VB.

Ooh me, ooh me, me, please teacher!

I wrote one of these ages ago, when I was still full of all that data
structures stuff they taught us in uni. IIRC, I used an array of user types
that included an integer to point to the index of the "next" array member.
Come to think of it, I think I did a dequeue too!

Then, of course, we all grew up and just used Collection objects because
that is what they are for!

All the best


Tim F

 

[Michael]

Thanks for putting me in the right path.

I found an example that showed me how to do "Linked List
in VB", which is what I was looking for:

http://www.freevbcode.com/ShowCode.asp?ID=6512

http://www.freevbcode.com/ShowCode.asp?ID=6511


Thanks,

Michael