Inconsisent(?) behaviour of str2num() with a particular usage
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The task in hand for me was to generate an empty array corresponding to the class/datatype of the input.
input = 'string';
output = char.empty
input = single(rand);
output = single.empty
My approach to this was to obtain the class of the input and use it with str2num -
input1 = "MATLAB";
str1 = sprintf('%s.empty', class(input1));
out1 = str2num(str1)
As you can see above, that the output is an empty array of double class and not of string class (as expected by me). This also occurs with char data-type
input2 = 'Batman'
str2 = sprintf('%s.empty', class(input2));
out2 = str2num(str2)
I have checked for these datatypes - single, double, all integer classes, figure, datetime, duration, calendarDuration, timeseries, string and char. It works for all the datatyes except for the last two.
I expected the code to work for all classes.
My questions are - Did I expect wrongly?
If not, why does this give incorrect (edit - different) output for 2 data types?
VBBV on 21 May 2023
Edited: VBBV on 21 May 2023
The function str2num can be used to convert the strings that inherently contain numbers to double class.
In your case there are no numbers in the outputs from sprintf function. Therefore, it results in empty  which belongs to double class by default.
The reason why it worked for other data types is that they all belong to or contain numbers except for char & string
Hope this clarifies