Reading a double value from a string

Question

I've tried to solve this for hours and absolutely don't understand what the compiler is doing here. I have strings that basically look like this:

"KL10124 Traitor #2 - +XX-+0.25 - More Stuff"

and need to read off the double '0.25' programmatically. Calling the string above s, the following two lines don't work:

string[] h = s.Split('-');
string h2 = h[2].Substring(1,h[2].Length - 2);
double d = Convert.ToDouble(h2);

The output if I display d is "25". I thought it might depend on the '.' resp ',' culture dependency, but if I insert

double d = Convert.ToDouble(h2.Replace('.',','));

it does not change a thing, the output is still "25".

But finally, if I do the brute force method as below I get the verbatim output "0,25" on the screen

double d;
string[] h = s.Split('-');
string h2 = h[2].Substring(1,h[2].Length - 2);
if (h2.Contains("."))
{
    string[] h3 = h2.Split('.');
    d = Convert.ToDouble(h3[0]) + Convert.ToDouble(h3[1])/100;
}
else
{
    d = Convert.ToDouble(h2);
}
return d;

Why exactly do the first two versions not work? The last bit of code cannot be the correct way to do this.

Your first example [works perfectly on ideone](http://ideone.com/tsRRe). — Sergey Kalinichenko, Aug 23 '12 at 13:49
If the string you are trying to parse has a known structure, why not investigate using the System.Text.RegEx classes to extract the number. — Ben Cawley, Aug 23 '12 at 13:49
Check this out: http://txt2re.com/index-csharp.php3?s=%22KL10124%20Traitor%20%232%20-%20%2bXX-%2b0.25%20-%20More%20Stuff%22&-7 — froeschli, Aug 23 '12 at 13:50
While I can't say I like the style employed, there seems to be nothing wrong on the face of it. Have you tried putting in Console.WriteLines between those 3 lines to see what h2 holds (and that there is the expoected number of spits in the h array) etc. — Wolf5370, Aug 23 '12 at 13:56
OOps, obv h2 = h. @Wolf5370, this is my beginners ad hoc solution, not claiming it to be good style, just the most obvious code to me. In asking this quetion, I was looking for better ways, so what would your style be? — EluciusFTW, Aug 23 '12 at 14:59
Well, as pointed out, better to use Double.Parse (or TryParse) with Invariant Culture - However, personally I would use RegEx as it would be easier and faster here I think (and less error prone). However, I'm not a style-cop - just pointing out that the code looks like it should work regardless. Important bit being - it SHOULD work. So, to find out why it isn't, you are going to need to break the code or Console out its progress. I suspect there is a difference in the string than you expect - or the code above is not an absolutely true reflection of the actual code. Good luck. — Wolf5370, Aug 23 '12 at 15:13

score 6 · Accepted Answer · answered Aug 23 '12 at 13:48

6

Try to use

double d = Convert.ToDouble(h2, CultureInfo.InvariantCulture);

instead of

double d = Convert.ToDouble(h2);

answered Aug 23 '12 at 13:48

Ilya Ivanov

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Thanks, this works. But could you please tell me why my code, even after replacing the '.' with ',' didn't work? – EluciusFTW Aug 23 '12 at 15:04
1

By default, comma in Convert.ToDouble is used to separate thousandths in number. For example "1,635,555" is Converted into 1635555. Thus, making you number "0,25" just emits number 25. – Ilya Ivanov Aug 23 '12 at 15:43

score 3 · Answer 2 · answered Aug 23 '12 at 13:52

3

A number of people have already mentioned using Regex. If you are not very familiar with Regex, then this page might help you:

http://txt2re.com/index-csharp.php3?s=%22KL10124%20Traitor%20%232%20-%20%2bXX-%2b0.25%20-%20More%20Stuff%22&-7

Cheers

answered Aug 23 '12 at 13:52

froeschli

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Thanks, indeed never heard of it. Will look at the link in detail. – EluciusFTW Aug 23 '12 at 15:08

score 3 · Answer 3 · answered Aug 23 '12 at 14:25

3

Try the Regex way :

string input = "KL10124 Traitor #2 - +XX-+0.25 - More Stuff";

Match match = Regex.Match(input, "^.*([0-9]+\\.[0-9]+).*$");

if (match.Success)
{
    double value = Convert.ToDouble(match.Groups[1].Value, CultureInfo.InvariantCulture);
    Console.Write(value);
}

answered Aug 23 '12 at 14:25

Anthony Simmon

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Thanks, will def. try out regex. – EluciusFTW Aug 23 '12 at 15:24

score 2 · Answer 4 · answered Aug 23 '12 at 13:47

2

d = double.Parse(h2,CultureInfo.InvariantCulture);

You need to set the format provider of the conversion operation to invariant.

answered Aug 23 '12 at 13:47

daryal

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Thx, this Works, but as in Ivanovs answer, I don't get why my code didn'T work after manually replacing '.' by ',' – EluciusFTW Aug 23 '12 at 15:07

score 1 · Answer 5 · edited May 23 '17 at 12:30

1

You should look at h2 before you convert. It looks like it does not include the decimal point. Convert.ToDouble might require the leading 0 to know it's a fraction also, I am not certain.

In general this is a lot easier with a regex. See this answer.

edited May 23 '17 at 12:30

Community

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answered Aug 23 '12 at 13:48

tallseth

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Thanks, but I did that and substring is OK including the 0. Didn't want to clutter to much code into the original Q. Will check out RegEx. – EluciusFTW Aug 23 '12 at 15:09

score 1 · Answer 6 · answered Aug 23 '12 at 13:50

1

Use a RegEx query like this:

^KL\d+ Traitor #\d \- \+XX\-\+(\d+\.\d+) \- .+

A grouping (expression in brackets) will give your the result.

See the sandbox.

answered Aug 23 '12 at 13:50

abatishchev

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Thanks, I will try regex. But it wont be quite as easy as in your code, becaus I was unclear in my Q: The word 'Traitor', the length of the string, the presence of "#2" are all flexible, but all the strings I need to read have the same structure in terms of the '-' character, which is why I opted to split the string at this charakter. – EluciusFTW Aug 23 '12 at 15:23
@ToaoG: Sure, I understood, my version of regex is more stric but you can make it less strict using `.+` meaning "any character or more". – abatishchev Aug 23 '12 at 15:48

score 0 · Answer 7 · answered Aug 23 '12 at 13:48

0

Print h2 in the first code example to see if you are doing the substring extraction correctly.

Also using a regular expression to extract the numer would more straigthforward.

answered Aug 23 '12 at 13:48

Tulains Córdova

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Yes, have checked all the obvious problems, like substring etc. numerous times, didn't want to clutter the Q with too much code. – EluciusFTW Aug 23 '12 at 15:05

score 0 · Answer 8 · answered Aug 23 '12 at 13:52

0

Use Regex

(?<=\+)([0-9\.])+

answered Aug 23 '12 at 13:52

msmucker0527

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Reading a double value from a string

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