C# > Convert string to double when input=""

Question

I would like to convert a string to double (very basic question isn't it ?)

string input = "45.00000";
double numberd = Double.Parse(input, CultureInfo.InvariantCulture);

=> my code works and I am very happy.

However I may have the following

string input = "";
double numberd = Double.Parse(input, CultureInfo.InvariantCulture);

In this case my code does not work and I get a Exception error ;( I wonder how I can manage such situation. Ideally when I get this I would like to have my variable numberd equal to null.

Can anyone help me ? Thx

dana · Accepted Answer · 2011-02-15 22:55:13Z

5

Microsoft recommends using the Tester-Doer pattern as follows:

string input = "";
double numberd;
if( Double.TryParse(input, out numberd) )
{
    // number parsed!
}

answered Feb 15, 2011 at 22:55

dana

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Comments

Fredrik Mörk · Accepted Answer · 2011-02-15 23:00:17Z

3

Use a Double for parsing, but a Double? for storing the value, perhaps?

Double number;
string input = ""; // just for demo purpose, naturally ;o)
Double? nullableNumber = 
    Double.TryParse(input, NumberStyles.Any, CultureInfo.InvariantCulture, out number) 
    ? (Double?)number 
    : null;

// use nullableNumber

answered Feb 15, 2011 at 23:00

Fredrik Mörk

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Comments

Daniel DiPaolo · Accepted Answer · 2011-02-15 22:55:28Z

1

Primitive types like double cannot be null. You can have a nullable version with double? but, Double.Parse does not return a double? (just a plain double).

You could use Double.TryParse and check the return condition and set a double? to null accordingly if that would suit better.

answered Feb 15, 2011 at 22:55

Daniel DiPaolo

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Comments

yan · Accepted Answer · 2011-02-15 22:56:09Z

1

Why not just catch the exception and set your variable?

double numberd;
try {
  numberd = Double.Parse(input, CultureInfo.InvariantCulture);
} catch (System.FormatException e)
  numberd = 0.0;
}

Alternatively, you can use Double.TryParse

answered Feb 15, 2011 at 22:56

yan

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Comments

Jeff · Accepted Answer · 2011-02-15 22:54:05Z

0

Add an if statement comparing strings or surround with try/catch block.

answered Feb 15, 2011 at 22:54

Jeff

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Comments

Kon · Accepted Answer · 2011-02-15 23:11:27Z

0

Assuming you aren't worried about other invalid values besides empty strings, here's a simple one-liner:

Double? numberd = (input.Length == 0) ? null : (Double?)Double.Parse(input, CultureInfo.InvariantCulture);

mzabsky was on the right path, however his solution won't build and you shouldn't hard-code empty string - it's better to check the length of a string.

answered Feb 15, 2011 at 23:11

Kon

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Comments

ThatAintWorking · Accepted Answer · 2013-04-24 20:02:04Z

0

How about

Double? numberd = String.IsNullOrEmpty(str) ? null : Double.Parse(str)

In my application, I am parsing CSV files and I want these empty strings to be zero so I return 0.0 instead of null and it's all good.

5 more

answered Apr 24, 2013 at 20:02

ThatAintWorking

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2 Comments

Bob. Over a year ago

You would have to guarantee that str is a number, since String.IsNullOrEmpty("word") returns false, causing Double.Parse(str) to fail. Double.TryParse would be a better choice since it returns a boolean whether it succeeded.

ThatAintWorking Over a year ago

Good catch except you can't use Double.TryParse in the ternary

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