Resize array so that ubound gives -1?

[ecxjoe]

Can you redim an array back to where ubound() returns -1?

Example:

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redim items() as integer

print ubound( items ) '- shows -1

redim preserve items( 0 )

print ubound( items ) '- shows 0

'- move array back to zero elements?
redim items() '- compile error
redim items( -1 ) '- runtime error

Instead of adding an additional variable to keep track of the number of items in the array ( e.g. "itemCount += 1: redim preserve items( itemCount-1 )" ), I was experimenting with keeping track of the item count by using only ubound() instead ( e.g. grab the item count when needed with "ubound( items )+1" ). But, if I need to remove items from the array, I like to resize it back down, ideally back to zero elements if needed, so that ubound() reports -1 again.

[badidea]

You can erase the array:

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dim as long b() 'no elements
print ubound(b)

redim b(0) '1 element with index 0
print ubound(b)

erase(b) 'no elements
print ubound(b)

So you have to add an 'if' statement. Example (part of a larger class):

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'remove from end of list
function pt_list.pop() as pt_dbl
	dim as pt_dbl pt_
	dim as integer ub = ubound(pt)
	if ub >= 0 then
		pt_ = pt(ub)
		if ub = 0 then
			erase pt
		else
			redim preserve pt(ub - 1)
		end if
	end if
	return pt_
end function

[ecxjoe]

Awesome! Thanks. :-)

[Pierre Bellisle]

...keeping track of the item count...

Note that having ubound() as -1 does not always mean there is zero item in an array...

lbound may be negative or above zero
redim items(-5 to -1)
redim items(5 to 9)

ubound may be negative or equal zero
redim items(-5 to -1)
redim items(-4 to 0)

In those cases, to get item count, you may use
itemCount = ubound(items) - lbound(items) + 1

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redim items(-5 to -1) : print lbound(items), ubound(items), ubound(items) - lbound(items) + 1; " element in array" '-5 -1 5
redim items(5 to 9)   : print lbound(items), ubound(items), ubound(items) - lbound(items) + 1; " element in array" ' 5  9 5
redim items(-4 to 0)  : print lbound(items), ubound(items), ubound(items) - lbound(items) + 1; " element in array" '-4  0 5

[fxm]

Another variant to test if an 'array' is empty:

• If @array(Lbound(array)) = 0
  • (no data buffer allocated)