How to validate numeric values which may contain dots or commas?

Question

I need a regular expression for validation two or one numbers then , or . and again two or one numbers.

So, these

Answer 1

In order to represent a single digit in the form of a regular expression you can use either:

[0-9] or \d

In order to specify how many times the number appears you would add

[0-9]*: the star means there are zero or more digits

[0-9]{2}: {N} means N digits

[0-9]{0,2}: {N,M} N digits or M digits

[0-9]{0-9}: {N-M} N digits to M digits. Note: M can be left blank for an infinite representation

Lets say I want to represent a number between 1 and 99 I would express it as such:

[0-9]{1-2} or [0-9]{1,2} or \d{1-2} or \d{1,2}

Or lets say we were working with binary display, displaying a byte size, we would want our digits to be between 0 and 1 and length of a byte size, 8, so we would represent it as follows:

[0-1]{8} representation of a binary byte

Then if you want to add a , or a . symbol you would use:

\, or \. or you can use [.] or [,]

You can also state a selection between possible values as such

[.,] means either a dot or a comma symbol

And you just need to concatenate the pieces together, so in the case where you want to represent a 1 or 2 digit number followed by either a comma or a period and followed by two more digits you would express it as follows: >

[0-9]{1,2}[.,]\d{1-2}

Also note that regular expression strings inside C++ strings must be double-back-slashed so every \ becomes \\