zeros before a string using num2str

I would like to pad zeros before a string. I have the following code:

a1 = 12.1521;

a2 = 2.1521;

b1 = num2str(a1,'%03.4f');

b2 = num2str(a2,'%03.4f');

The result is b1 = '12.1521';

The result is b2 = '2.1521';

I would like to obtain the result b1 = '012.1521' and b2 = '002.1521'

Answer 1

[Guillaume]

The problem with your format string is not the %0 which would work fine, had the next number been correct. The 3 is the problem. In both %3.4f and %03.4f it is ignored as the value is too small. It should always be more than the value after the . since it specifies the minimum total number of characters to print.

Try

num2str(a1, '%08.4f')   %8 since you want 4 digits after the . + 1 digit for the . + 3 digit s before

[JG]

This isn't working for me. Did this behavior change in a later version of MatLab?

[JG]

It is working, the 0 before the 8 matters.

Answer 2

[Adam]

b = num2str(a,'0%3.4f')

[fdb]

I would like to automatically pad the number of leading zeros, depending on the formatting I specify (in this case 3 digits leading the comma, and 4 digits following the comma). It should also work if I don't know beforehand what the number a1 is.

Answer 3

[KL]

Try this

A = [69.45 31.71 95.36 3.44 7.82]'
str = string(A)
newStr = pad(str,7,'left','0') %or pad(str,7,'both','0')

read more here: https://www.mathworks.com/help/matlab/ref/pad.html