Find hashtags in string

Question

I am working on a Xamarin.Forms PCL project in C# and would like to detect all the hashtags.

I tried splitting at spaces and checking if the word begins with an # but the problem is if the post contains two spaces like "Hello #World Test" it would lose that the double space

string body = "Example string with a #hashtag in it";
        string newbody = "";
        foreach (var word in body.Split(' '))
        {
            if (word.StartsWith("#"))
                newbody += "[" + word + "]";
            newbody += word;
        }

Goal output:

Example string with a [#hashtag] in it

I also only want it to have A-Z a-z 0-9 and _ stopping at any other character

Test #H3ll0_W0rld$%Test => Test [#H3ll0_W0rld]$%Test

Other Stack questions try to detect the string and extract it, I would like it work with it and put it back in the string without losing anything that methods such as splitting by certain characters would lose.

Answer 1

You can use Regex with #\w+ and $&

Explanation

• # matches the character # literally (case sensitive)
• \w+ matches any word character (equal to [a-zA-Z0-9_])
• + Quantifier — Matches between one and unlimited times, as many times as possible, giving back as needed (greedy)

$& Includes a copy of the entire match in the replacement string.

Example

var input = "asdads sdfdsf #burgers, #rabbits dsfsdfds #sdf #dfgdfg";
var regex = new Regex(@"#\w+");
var matches = regex.Matches(input);
foreach (var match in matches)
{
    Console.WriteLine(match);
}

or

var result = regex.Replace(input, "[$&]" );
Console.WriteLine(result);

Ouput

#burgers
#rabbits
#sdf
#dfgdfg
asdads sdfdsf [#burgers], [#rabbits] dsfsdfds [#sdf] [#dfgdfg]

Updated Demo here

Another Example