[:punct:] vs [[:punct:]]

[JUAN DENT]

Hi,

What is the difference between:

[:punct:]+

and

[[:punch:]]+

??

Thanks
Juan

[TarikNeaj]

uhm... what? Is this c++?

[JUAN DENT]

these are Regular expressions character classes (used in regex)

[TheIdeasMan]

http://www.cplusplus.com/reference/regex/ECMAScript/#character_classes

I found this:

[abc[:digit:]] is a character class that matches a, b, c, or a digit.

So presumably one could do :

[abc[:punct:]] which would match punctuation as well as a b c.

So it looks like no difference between :

[:punct:] and [[:punct:]]

Hope that helps :+)

[z05DSL3A]

There is a difference...

#include <iostream>
#include <regex>
#include <string>

using namespace std;

int main()
{
    string input;
    
    regex punct1("[:punct:]+");
    regex punct2("[[:punct:]]+");
    
    while(true)
    {
        cout<<"Give me punct!"<<endl;
        cin>>input;
        if(!cin) break;
        //Exit when the user inputs q
        if(input=="q")
            break;
        if(regex_match(input,punct1))
            cout<<"is in :punct:"<<endl;
        else
        {
            cout<<"Invalid input"<<endl;
        }
        if(regex_match(input,punct2))
            cout<<"is punct"<<endl;
        else
        {
            cout<<"Invalid input"<<endl;
        }
    }
}

Give me punct!
p
is in :punct:
Invalid input
Give me punct!
,
Invalid input
is punct
Give me punct!

So
[:punct:] = the set of characters ;punct:
[[:punct:]] = the set that includes the subset of punctuation characters.

[JUAN DENT]

Yes, I ran it and they are different...

I tested by inputing comma or period and that is NOT matched by [:punct:]+ but IS MATCHED by [[:punch:]]+

On the other hand, if input is :, then it is matched by both!!

I GOT IT!! Thanks