Can someone explain this please? (RESOLVED)

[srod]

The following runs fine:

Code: Select all

Dim a(10)
Dim b(10)

a(0) = 1
a(1) = 2

b()=a() ;b should now point to a.

Debug b(1) ;Displays 2 as expected.

However, the following does not display the correct result. It should be functionally identical to the above.

Code: Select all

Dim a(10)

a(0) = 1
a(1) = 2

Procedure Test(addy)
  Dim b(10)
  b()=addy
  Debug b(1)  ;Should display 2 !
EndProcedure

Test(a())

??? I'm probably doing something daft!

[Tranquil]

Are you sure that A() = B() is a valid operation!? Never thought about this. Sure, A() returns something like a pointer. Is this new on PB4?

[Paul]

Remember that Dim is no longer Global by default in PureBasic 4.

Did you try adding Global in front of both your Dim commands so the data can be shared?

[srod]

Thanks for the replies.

Paul: I wish to avoid using global arrays at the moment, but that would of course solve this problem - although it doesn't explain why the code doesn't run as is!

Tranquil: no, it's not new on PB4, I used to use this all the time with PB3.94 etc. Although this was of course where all arrays were global etc.

Strange, the statement

Code: Select all

b()=a()

has no affect when used in a procedure, even if both arrays are DIMensioned within the procedure itself. This would appear to be the root of the problem.

[Tranquil]

I searched through the whole PB referenze and I can not find any hint that your expression is valid.

Maybe its a bug that it even works. Normaly the () indicates a linked list.

[josku_x]

Well, be quiet before Fred fixes that bug

[srod]

I think it's well known that a() gives the base address of the array. Indeed, in PB4, you use this to pass an array to a procedure. The expression b()=a() is probably not documented (or encouraged ), however I've seen it used quite a lot.

Oh well, I'll need to take another tact all together.

[Kale]

Related to this?:
http://www.purebasic.fr/english/viewtopic.php?t=21081

[netmaestro]

If you were going to code that, I believe this would be right:

Code: Select all

Dim a(10) 

a(0) = 1 
a(1) = 2 

Procedure Test(addy(1)) 
  Dim b(10) 
  b()=addy()
  Debug b(1)  ;Should display 2 ! 
EndProcedure 

Test(a()) 

However, it fails because even though the procedure knows the correct address of the a() array, it refuses to assign it to b() because they do not share the same scope. So I don't believe it is expected to work.

[srod]

Yea, I looked at that. It could be (at least in that I guess the code I'm using is probably to be discouraged!) Still, it's strange that the 'trick' works outside of procedures, but not within.

[srod]

netmaestro, the following doesn't work either although both arrays share the same scope:

Code: Select all

Procedure Test()
Dim a(10)
Dim b(10)

a(0) = 1
a(1) = 2
b()=a()

Debug b(1)  ;Should display 2 !
EndProcedure

test()

[josku_x]

Try with Macro? maybe it works

[netmaestro]

You probably won't like this because it copies the whole array, but I'll offer it anyway just in case:

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Dim a(10) 

a(0) = 1 
a(1) = 2 

size = PeekL(@a()-8) * SizeOf(long)

Procedure Test(loc,size) 
  Dim b(10) 
  CopyMemory(loc,b(),size)
  Debug b(1)  ;Should display 2 ! 
EndProcedure 

Test(a(),size) 

[netmaestro]

This works:

Code: Select all

Dim a(10) 

a(0) = 1 
a(1) = 2 

Procedure Test(addy) 
  Static Dim b(10) 
  b()=addy
  Debug b(1)  ;Should display 2 ! 
EndProcedure 

Test(a()) 

[josku_x]

so it's all about using static, right?

these *undocumented* things drive me crazy