从字符串C＃中提取双精度值

Question

I want to extract the double from my string.

buff = "VA VV_CELL1 3.55"

When i use the following code

private void GetLine(string msg, string buff, double numb)
{
    comPort.WriteLine(msg); 
    Thread.Sleep(50);
    buff = comPort.ReadExisting();
    Thread.Sleep(50);
    MatchCollection matches = Regex.Matches(buff, @".*?([-]{0,1} *\d+.\d+)");
    List<double> doubles = new List<double>();
    foreach (Match match in matches)
    {
        string value = match.Groups[1].Value;
        value = value.Replace(" ", "");
        doubles.Add(double.Parse(value));
        Thread.Sleep(200);
        numb = doubles[0];                
    } 
}

This code work for my other strings but "CELL1" contains a number so i dont get the wanted value "3.55" any ideas?

Answer 1

Why you don't simply split this string and take the last part?

string numberPart = buff.Split().Last();
double num;
bool validNum = double.TryParse(numberPart, NumberStyles.Any, CultureInfo.InvariantCulture, out num);

Another way is to use Substring and LastIndexOf (which fails if there is no space):

string numberPart = buff.Substring(buff.LastIndexOf(' ')).Trim();

---

To help on your comment :

I'd use a method that returns a double? (double that can be null):

double? GetNumber(string buff)
{
    string numberPart = buff.Split().Last();
    double num;
    bool validNum = double.TryParse(numberPart, NumberStyles.Any, CultureInfo.InvariantCulture, out num);
    if (validNum)
        return num;
    else
        return null;
}

Now you can use the method and you even know whether the number could be parsed successfully or not:

double? result = GetNumber("VA VV_CELL1");
bool wasValid = result.HasValue;
if(wasValid)
{
   double value = result.Value;
}

Answer 2

试试这个正则表达式： \\s+\\d+(.)?\\d+

Answer 3

I assume you want to capture both doubles and integers, otherwise you could write \\d+\\.\\d+ . This :

Regex.Matches("VA VV_CELL1 3.55",@"\d+\.\d+")[0]

Returns 3.55 but can't capture 355.

You can capture an integer or decimal preceded by whitespace with \\s+\\d+(\\.\\d+)? .

Regex.Matches("VA VV_CELL1 3.55",@"\s+\d+(\.\d+)?")[0]

Returns 3.55 while

Regex.Matches("VA VV_CELL1 355",@"\s+\d+(\.\d+)?")[0]

Returns 355

If you want to capture only the last field you can use \\s+\\d+(\\.\\d+)?$ ,eg:

Regex.Matches("VA VV_CELL1 3.54 3.55",@"\s+\d+(\.\d+)?$")[0]

Returns 3.55

You don't need to trim whitespace because double.Parse ignores it. You can change the pattern to capture the number in a separate group though, by surrounding the digits with parentheses :

Regex.Matches("VA VV_CELL1 3.54 3.55",@"\s+(\d+(\.\d+)?)$")[0].Groups[1]

You need to use Groups[1] because the first group always returns the entire capture