Turning a char element in a double array

How can I turn a char element into an array of double values. I am trying to get the Expected Output below but array_convert does not work. How would I be able to get the Expected Output below?

Code:

a = char('[21,12,43,1]')
array_convert= str2double(a)

Expected Output:

[21  12  43  1]

Answer 1

[the cyclist]

a = char('[21,12,43,1]');
array_convert = str2num(a)

array_convert = 1×4

21 12 43 1