Oxygen Basic

Programming => Example Code => Topic started by: Brian Alvarez on November 30, 2018, 01:04:53 AM

Title: Request for an example of UDT member pointers
Post by: Brian Alvarez on November 30, 2018, 01:04:53 AM

 If somebody can provide an example for this, i would appreciate it.

 I see that TYPE allows PTR members,

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TYPE SOMETHING
     SOMETHING AS LONG PTR
END TYPE
How can those be used?

Title: Re: Request for an example of UDT member pointers
Post by: Charles Pegge on November 30, 2018, 01:59:13 AM

A simple demo for setting pointered members:

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type tt
  pf as float ptr
end type

dim t as tt
dim f as float=pi()
@t.pf=@f
print t.pf


Title: Re: Request for an example of UDT member pointers
Post by: Brian Alvarez on November 30, 2018, 02:14:57 AM

I think i understand. I would need to split the assignation into several statements, right?
The way i am trying to emulate is this, suppose i have a variable for an UDT PTR. As follows:

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type tt
  pf as float ptr
end type

dim t as tt ptr
The way i would do it in PowerBASIC would be to aquire an address for t like this:

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t = hAddress
And then i would need to aquire an address for pf, as follows:

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@t.pf = hAddress
Then i would access pf member as follows:

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@t.@pf = 123
There can even bee deeply nested pointers like this:

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@t.@pf.@tree.@yikes = 1234
Am i right to assume in Oxygen i need to do this?

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@t = hAddress1
@t.pf = hAddress2
@t.pf.tree = hAddress3
@t.pf.tree.yikes = hAddress4

And if so... am i right to assume this would return the address of an UDT member 'yikes':

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print str(@t.pf.tree.yikes)
While this returns the value stored in the member?

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print str(t.pf.tree.yikes)

Title: Re: Request for an example of UDT member pointers
Post by: Charles Pegge on November 30, 2018, 03:16:29 AM

Yes, this is correct.

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@t = hAddress1
@t.pf = hAddress2
@t.pf.tree = hAddress3
@t.pf.tree.yikes = hAddress4
'
print str(t.pf.tree.yikes)

Fortunately, direct deep pointering is seldom required , though recursive tree stuructures are quite useful.

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type tt
   pt as tt ptr 'recursive structure
   dat[16] as int
end type


Title: Re: Request for an example of UDT member pointers
Post by: Brian Alvarez on November 30, 2018, 03:45:45 PM

This is a new concept to me charles, how does it work?

Perhaps i can make use of it. :)

Title: Re: Request for an example of UDT member pointers
Post by: Charles Pegge on December 03, 2018, 03:52:22 AM

A structure can refer to itself using a pointer member, without causing any recursion problems.

You can use it as a node for linked lists, tree structures and networks.

Here is a silly example, but it tests the notation:

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'11:38 03/12/2018
'UDT SELF REFERENCE TEST
type tt
  int a,b,c
  tt* t
end type

tt t
@t.t=@t
t={1,2,3}
print t.b
print t.t.b
print t.t.t.b