Regular expression to match input of n words separated by m spaces

Question

So I'm learning regular expressions in c++11 and i'm trying to create a regular expression to match an input of N words separeted by M spaces. So, for example, you input " word word word word ..." and you can continue like this for how long you like.

Now my problems come when I try to access the fields in the smatch variable after comparing an input to the regular expression. At the moment what I have is:

#include <regex>

regex input_reg(
    "(?:[[:space:]]*"
    "([[:alpha:]_]+)"
    "[[:space:]]*)+");

smatch comparison;
if (regex_match(input, comparison, input_reg)){
            for (smatch::size_type i = 0; i < comparison.size(); ++i){
                cout << i << ": '" << comparison.str(i) << "'" << endl;
            }
        }

The problem with this is that for some reason, I get a match as I should but when I try to cout all the fields to see if it works I only get the initial match and the first field, nothing else:

0: ' word word            word  word '
1: 'word'

What am I doing wrong?

EDIT: The input is as seen in cout example of my code, it doesn't show all the spaces in the text for some reason.

A common error: a repeated capturing group only stores the *last* captured value. Now, do you need to actually *validate* the string? Why not tokenize it with whitespace(s) as separator? — Wiktor Stribiżew, Dec 15 '16 at 13:31
I recommend [regex101](https://regex101.com/) for experimentation while developing regular expressions. — Some programmer dude, Dec 15 '16 at 13:35
@WiktorStribiżew: Your first sentence looks like a good answer to me (unless you can find a duplicate to point at). — Martin Bonner supports Monica, Dec 15 '16 at 13:38
@WiktorStribiżew I'm not certain what u mean by validating the string. I need to capture the words to easily access and use them later. — Darkonode, Dec 15 '16 at 14:17
Cool, then use `[[:alpha:]_]+` regex with `std::sregex_iterator` as shown in [my answer](http://stackoverflow.com/a/40390658/3832970). — Wiktor Stribiżew, Dec 15 '16 at 14:21
Yes, this is exactly what I was looking for! I didn't find it earlier because apparently, I didn't quite know what I was looking for. Thanks! — Darkonode, Dec 15 '16 at 14:47

Regular expression to match input of n words separated by m spaces

0 Answers0