finding occurrences of string within a string

What is the quickest and most efficien开发者_如何学Pythont way of finding a string within another string.

For instance I have this text;

"Hey @ronald and @tom where are we going this weekend"

However I want to find the strings which start with "@".

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You can use Regular expressions.

string test = "Hey @ronald and @tom where are we going this weekend";

Regex regex = new Regex(@"@[\S]+");
MatchCollection matches = regex.Matches(test);

foreach (Match match in matches)
{
    Console.WriteLine(match.Value);
}

That will output:

@ronald
@tom

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You need to use Regular Expressions:

string data = "Hey @ronald and @tom where are we going this weekend";

var result = Regex.Matches(data, @"@\w+");

foreach (var item in result)
{
    Console.WriteLine(item);
}

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try this one:

string s = "Hey @ronald and @tom where are we going this weekend";
var list = s.Split(' ').Where(c => c.StartsWith("@"));

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If you are after speed:

string source = "Hey @ronald and @tom where are we going this weekend";
int count = 0;
foreach (char c in source) 
  if (c == '@') count++;   

If you want a one liner:

string source = "Hey @ronald and @tom where are we going this weekend";
var count = source.Count(c => c == '@'); 

Check here How would you count occurrences of a string within a string?

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String str = "hallo world"
int pos = str.IndexOf("wo",0)