How to avoid empty array elements when making JSON out of structures?

[Quin]

I have this code. It works as expected, accept the generated JSON has one more item in the array than I'd expect, an empty string. Is this because of how PureBasic's Dim/ReDim keywords work? If so, is there a way around it?

Code: Select all

EnableExplicit

Structure JSON
Array Test$(0)
EndStructure

Global NewList Names$()
AddElement(Names$()) : Names$() = "Quin"
AddElement(Names$()) : Names$() = "Sam"
AddElement(Names$()) : Names$() = "Malia"

Define j.JSON, Size.i
ForEach Names$()
Size = ArraySize(j\Test$()) + 1
ReDim j\Test$(Size)
j\Test$(Size - 1) = Names$()
Next
Define JSONID.i = CreateJSON(#PB_Any)
InsertJSONStructure(JSONValue(JSONID), @j, JSON)
Debug ComposeJSON(JSONID)
FreeJSON(JSONID)

[Andesdaf]

Yes it's because ReDim(Size) creates Size+1 elements. You could ReDim with Size-1 in the end or do the first ReDim only in the second iteration of the ForEach loop:

Code: Select all

Define j.JSON, Size.i
Size = ArraySize(j\Test$())
ForEach Names$()
  If ListIndex(Names$()) > 0
    Size + 1
    ReDim j\Test$(Size)
  EndIf
  j\Test$(Size) = Names$()
Next

but that is only safe if the array is initially empty.

[Quin]

Yes it's because ReDim(Size) creates Size+1 elements. You could ReDim with Size-1 in the end or do the first ReDim only in the second iteration of the ForEach loop:

Code: Select all

Define j.JSON, Size.i
Size = ArraySize(j\Test$())
ForEach Names$()
  If ListIndex(Names$()) > 0
    Size + 1
    ReDim j\Test$(Size)
  EndIf
  j\Test$(Size) = Names$()
Next

but that is only safe if the array is initially empty.

I know the array will always be empty, I explicitly check for that, so that's okay.
Thanks for your help, this works!

[NicTheQuick]

It's not a good idea to constantly use ReDim in each iteration. When there are a lot of elements in the LinkedList ReDim is called on each element which means that in the background a lot of copying is be done in the worst case. Don't do that.
Just ReDim once before the loop and use a variable to iterate through the indexes:

Code: Select all

EnableExplicit

Structure JSON
	Array Test$(0)
EndStructure

Global NewList Names$()
AddElement(Names$()) : Names$() = "Quin"
AddElement(Names$()) : Names$() = "Sam"
AddElement(Names$()) : Names$() = "Malia"

Define j.JSON, i.i = 0
ReDim j\Test$(ListSize(Names$()) - 1)
ForEach Names$()
	j\Test$(i) = Names$()
	i + 1
Next
Define JSONID.i = CreateJSON(#PB_Any)
InsertJSONStructure(JSONValue(JSONID), @j, JSON)
Debug ComposeJSON(JSONID)
FreeJSON(JSONID)

For some reason this also works if there are no elements in the LinkedList although ReDim should throw an error because it is called with a negative size.

Edit: FYI: I created another topic regarding the size of -1 here: https://www.purebasic.fr/english/viewtopic.php?t=86812