Unexpected behaviour from ishandle()

Hi,

In a script, I was checking the existence of a plot handle to either make a new plot or to change the x/y data. Surprisingly this didn't work by initially setting the plot handle to []. Reason:

>> ishandle( [] )
ans =
     []

which sort of makes sense.

However, my next step was to initialise the plot handle to 0, which also didn't work, and this was the real surprise:

>> ishandle( 0 )
ans =
     1

Even though

>> ishandle( 1 )
ans =
     0

Does anybody why zero would be a valid graphics or Java object handle?

Thanks,

Temu

[Temu Gautama]

I forgot to check the forum. Apparently, 0 is the root handle.

Temu

Answer 1

[Stephen23]

On MATLAB versions prior to R2016b zero is the handle to the graphics root (i.e. the parent of all graphics figures):

https://www.mathworks.com/help/matlab/graphics-objects.html

For compatilbility using zero is still permitted in later versions.

https://www.mathworks.com/help/matlab/ref/groot.html