How to make a regular expression recognise whitespace in html element

Question

I'm new to regular expressions in C++ and was wondering if anyone could tell me what I'm doing wrong here, i'm trying to make a regular expression match a html element, using the code i have i can make it match in all cases except where there is whitespace separating the content from the tags

string opening_tag = "(<[[:alpha:]]+>)";   
string content = "([\\w ]*)";   // zero or more characters or spaces
string closing_tag = "(</[[:alpha:]]+>)";
string html_element = opening_tag + content + closing_tag;

regex r(html_element);

string s;
while (cin >> s)
{
    if (regex_match(s, r))
    {
        cout << "matched" << endl;
    }
}

Try replacing the space with `\s` for whitespace characters: `[\\w\\s]*` — Sam, Jun 09 '14 at 19:16
Hi thanks for reply I tried that but didn't work unfortunately — user3723523, Jun 09 '14 at 19:20
[this answer](http://stackoverflow.com/a/1732454/1090079) is where *stackoverflow* stands on parsing html using *regular expressions*, it's very relevant. — Filip Roséen - refp, Jun 09 '14 at 19:25

score 2 · Accepted Answer · edited Jun 20 '20 at 09:12

Introduction

Your problem is actually not related to the regular-expression itself, but to how you are reading your data.

Explanation

When using operator>> you are effictively reading "word" by "word", since the operator will read as many characters as it can find, until it hits a whitespace (whitespaces are ignored by operator>>).

If you'd like to read an entire line from std::cin and store it in string s, you should use std::getline, as in the below sample snippet:

while (std::getline (std::cin, s)) {
  ...
}

^{Note: The regular expression constructed in your snippet is legal C++, there are however implementations who don't fully support the usage of character classes such as \w. As an example, if you are using libstdc++ you must replace the usage of \w with the equivalent [_[:alnum:]], making string content = "([_[:alnum:] ]*)".}

Hi Filip Thanks for reply feel silly for not spotting that its working now thanks very much — user3723523, Jun 09 '14 at 19:51

How to make a regular expression recognise whitespace in html element

1 Answers1

Introduction

Explanation