Find number of decimal digits of a variable in MATLAB

Given a variable x = 12.3442

I want to know the number of decimal digits of the variable. In this case the result would be 4. How can I do this without trial and error?

As mentioned in the comments, the "number of decimal digits" does not make sense in most cases, but I think that this may be what you're looking for:

>> num = 1.23400;
>> temp = regexp(num2str(num),'\.','split')

temp = 

    '1'    '234'
>> length(temp{2})

ans =

    3