我需要一些文本解析帮助（正则表达式/C#）

Question

I could use a little help with proper regular expressions to parse the following string into 3 variables. The part with comments saying // TODO: is where I need help with the regular expressions. For now I have just assigned a static value, but need to replace that with real regular expressions that parse the sample text. Thanks!

// This is what a sample text will look like.
var text = "Cashpay @username 55 This is a sample message";

// We need to parse the text into 3 variables.
// 1) username - the user the payment will go to.
// 2) amount - the amount the payment is for.
// 3) message - an optional message for the payment.
var username = "username"; // TODO: Get the username value from the text.
var amount = 55.00; // TODO: Get the amount from the text.
var message = "This is a sample message"; // TODO: Get the message from the text.

// now write out the variables
Console.WriteLine("username: " + username);
Console.WriteLine("amount: " + amount);
Console.WriteLine("message: " + message);

Answer 1

You can use capturing groups:

var regex = new Regex(@"^Cashpay\s+@([A-Za-z0-9_-]+)\s+(\d+)\s+(.+)$");
var text = "Cashpay @username 55 This is a sample message";

var match = regex.Match(text);

if (!match.Success)
    //Bad string! Waaaah!

string username = match.Groups[1].Value;
int amount = int.Parse(match.Groups[2].Value);
string message = match.Groups[3].Value;

Answer 2

This method does not do input validation; in some cases this might be ok (eg the input is coming from a source which has already been validated). If you are getting this from user input you should probably use a method that is more robust. If it is coming from a trusted source but has multiple formats (eg "Cashpay" is one of many choices) you could use a switch or if statement for flow control after the split:

// make sure you validate input (coming from trusted source?) 
// before you parse like this.

string list[] = text.Split(new char [] {' '});

if (list[0] == "Cashpay")
{
    var username = list[1].SubString(1);
    var amount = list[2];
    var message = string.Join(' ',list.Skip(3));
}

or

// make sure you validate input (coming from trusted source?) 
// before you parse like this.

string list[] = text.Split(new char [] {' '},4);

if (list[0] == "Cashpay")
{
    var username = list[1].SubString(1);
    var amount = list[2];
    var message = list[3];
}