Error TryParse with negative numbers

Question

I had a problem with TryParse working correctly for me. I have a list of values ​​that I'm pretty sure are valid (since they come from another component in our system), but I would like to make sure that there is proper error handling in place.

Here is an example of a list of my values:

20.00
20.00
-150.00

And here is the method I originally wrote:

private decimal CalculateValue(IEnumerable<XElement> summaryValues) { decimal totalValue = 0; foreach (XElement xElement in summaryValues) { decimal successful; Decimal.TryParse(xElement.Value, out successful); if (successful > 0) totalValue += Decimal.Parse(xElement.Value); } return totalValue; } 

The variable "success" returned false for -150.00, so I added NumberStyles:

 private decimal CalculateValue(IEnumerable<XElement> summaryValues) { decimal totalValue = 0; foreach (XElement xElement in summaryValues) { decimal successful; Decimal.TryParse(xElement.Value, NumberStyles.AllowLeadingSign, null, out successful); if (successful > 0) totalValue += Decimal.Parse(xElement.Value, NumberStyles.AllowLeadingSign); } return totalValue; } 

However, now that I have NumberStyles, none of the numbers will be parsed! I’m good that IFormatProvider is set to null, because that’s all on our system. Does anyone see what I can do wrong?

Answer 1

Other answers have the right idea regarding the proper use of Decimal.TryParse . However, if I were to write this method, I would use LINQ to work with LINQ-to-XML objects:

 private decimal CalculateValue(IEnumerable<XElement> summaryValues) { return summaryValues .Sum(el => { decimal value; if (Decimal.TryParse(el.Value, out value)) return value; return 0M; }); } 

This version works the same way, but uses the Enumerable.Sum method to calculate the total. All I have to provide is a built-in function that extracts decimal values ​​from XElement.

Answer 2

This is not how you should use TryParse.

TryParse returns a boolean value (true / false), so your code should be:

 private decimal CalculateValue(IEnumerable<XElement> summaryValues) { decimal totalValue = 0; foreach (XElement xElement in summaryValues) { decimal valueReturned; bool successful = Decimal.TryParse(xElement.Value, out valueReturned); if (successful) totalValue += valueReturned; } return totalValue; } 

or more succinctly,

 private decimal CalculateValue(IEnumerable<XElement> summaryValues) { decimal totalValue = 0; foreach (XElement xElement in summaryValues) { decimal valueReturned; if (Decimal.TryParse(xElement.Value, out valueReturned)) totalValue += valueReturned; } return totalValue; } 

Answer 3

Others explain how to do it right, but do not explain what you are doing wrong.

If you use the “successful” above, this is not the meaning of success, this is the actual number that is being analyzed. Therefore, if you parse "-150.00", of course, successful will be negative. The original TryParse value is the actual parsed value, and the boolean value indicates whether the process was successful or not - this is the return value. Using what you need to understand would be something like:

 string inputValue = "-150.00"; decimal numericValue; bool isSucessful = Decimal.TryParse(inputValue , out numericValue); 

In this case, isSuccessful will be TRUE, numericValue will be -150. When you use user-entered values ​​and not hard-coded ones that I used above, you want to check:

 if(isSuccessful) { // Do something with numericValue since we know it to be a valid decimal } else { // Inform User, throw exception, etc... as appropriate, Don't use numericValue because we know it wrong. } 

Answer 4

your successful result will be negative when analyzing a negative value. your if (successful > 0) is what disconnects you.

If they are almost positively valid values, try using Convert.ToDecimal :

 decimal val = Convert.ToDecimal(xElement.Value); 

Otherwise, change the logic a bit:

 decimal val; if (Decimal.TryParse(xElement.Value, out val)){ // valid number } 

Answer 5

I suggest you tell XElement, the value of node, which should look like this:

 XElement.Element("nodename").Value 

Instead of XElement.Value. at least that's what i would do :)

Answer 6

Came from Google. The answer for me was that the incoming culture was wrong - especially in the incoming JSON file.

Use

 totalValue += decimal.Parse(xElement.Value, NumberStyles.Any, CultureInfo.InvariantCulture); 

or

 bool successful = decimal.TryParse(xElement.Value, NumberStyles.Any, CultureInfo.InvariantCulture, out value);