Why does a for loop iterate over an empty column vector?

A for loop in my code was executing unexpectedly. I had provided it with an empty column vector, and I had supposed that it would not execute. However it does iterate once, as this simple example shows:

>> bob = intersect([1;2;3],[4;5;6])

bob =

0×1 empty double column vector

>> for ii = bob; disp('executed an iteration'); end

executed an iteration

This behavior is not observed when iterating over an empty vector or an empty row vector, as shown below:

>> for ii = []; disp('executed an iteration'); end

>> fred = intersect([1,2,3],[4,5,6])

fred =

1×0 empty double row vector

>> for ii = fred; disp('executed an iteration'); end

Is this expected and/or desired behavior for a for loop to iterate over an empty column vector?

Answer 1

[Matt J]

Yes, I'm sure it's expected. There will be as many iterations as there are columns of "bob".

k=0;
for bob=zeros(0,5)
    
    k=k+1,
    
end

k = 1

k = 2

k = 3

k = 4

k = 5

Answer 2

[Bruno Luong]

Yes this is expected.

The for-loop iterates on the number of columns of an array, regardless the number of row

for c = A
    ...
end

is equivalent to

for j=1:size(A,2)
    c = A(:,j);
    ...
end