Handle Parse to Float, when input is Null

Question

I want to parse a string to float. And when the string is null it will pass 0 (as a float valule).

I was doing the parse like this :

aeVehicle.MSRP = float.Parse((drInvetory["MSRP"] ?? "0").ToString());

Which gave errors :

ERROR MESSAGE : Input string was not in a correct format.
ERROR SOURCE :    at System.Number.StringToNumber(String str, NumberStyles options, NumberBuffer& number, NumberFormatInfo info, Boolean parseDecimal)
   at System.Number.ParseSingle(String value, NumberStyles options, NumberFormatInfo numfmt)
   at System.Single.Parse(String s, NumberStyles style, NumberFormatInfo info)
   at System.Single.Parse(String s)

Please suggest the best way to handle this situation.

Community · Accepted Answer · 2017-05-23 11:46:28Z

11

If drInvetory["MSRP"] comes from a DataRow, the null coalescing operator will not evaluate to true when compared to DBNull, thus the float parse will fail. You can compare for DBNull.Value, or use float.TryParse().

From Original Code

aeVehicle.MSRP = float.Parse(drInvetory["MSRP"] == DBNull.Value ? "0" : drInvetory["MSRP"].ToString());

Personally, I would check for DBNull and then cast to a float (or unbox to exact type, then cast). This saves a comparatively expensive string parse.

Better

aeVehicle.MSRP = drInvetory["MSRP"] == DBNull.Value ? default( float ) : 
(float)drInvetory["MSRP"];

SQL-CLR type mapping: http://msdn.microsoft.com/en-us/library/bb386947.aspx
See also: Difference between decimal, float and double in .NET?

edited May 23, 2017 at 11:46

CommunityBot

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answered Sep 20, 2012 at 7:02

Tim M.

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6 Comments

A Developer Over a year ago

Never knew this..Yes..it comes from a DataRow

A Developer Over a year ago

@Tim Medora..i double checked this..you are right..you taught me a great thing today..Thanks

pero Over a year ago

From question seems that drInvetory["MSRP"] returns string. If so this will throw a exception: (float)drInvetory["MSRP"]. Better to use Convert.ToSingle()

Marc Gravell Over a year ago

@Petar no, it returns object. object can be null-coalesced with string - the result is an object expression; then the existing code calls .ToString() for the Parse. With that information, we can't really make any presumptions about what drInvetory["MSRP"] actually is. If it is actually a boxed float, then I agree with the "Better". If it is actually a string that happens to have a numeric-looking value, then Parse.

A Developer Over a year ago

"MSRP" field is "Money" type in sql server. I fetch this and stores in a DataTable.

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John3136 · Accepted Answer · 2012-09-20 07:01:55Z

0

float f = 0f;
string s = (drInvetory["MSRP"] ?? "0").ToString();
if (s != null) {
    f = float.Parse(s, ...
}

answered Sep 20, 2012 at 7:01

John3136

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3 Comments

Marc Gravell Over a year ago

0.0 is a double; 0f would be better, or just 0.

John3136 Over a year ago

Thanks - been in Java land today (no excuse, 0.0 is double in java too).

pero Over a year ago

Why ToString() ? It is already a string. And s cannot be null, so if seems not necessary. If drInvetory["MSRP"] is not a string this will not compile I think.

meirrav · Accepted Answer · 2012-09-20 07:04:22Z

0

you should use the the TryParse :

    float num = 0;
    float.TryParse(s, out num);

answered Sep 20, 2012 at 7:04

meirrav

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Comments

Niyoko · Accepted Answer · 2012-09-20 07:06:03Z

0

It might caused by unexpected comma in your string. Try to throw away the comma first.

answered Sep 20, 2012 at 7:06

Niyoko

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Comments

CodeSpeaker · Accepted Answer · 2012-09-20 07:07:53Z

0

float result = 0;
float.TryParse(drInvetory["MSRP"], out result);
aeVehicle.MSRP = result;

This way, if the parse fails, then it will always fall-back to 0.

answered Sep 20, 2012 at 7:07

CodeSpeaker

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Comments

Manpreet Singh Dhillon · Accepted Answer · 2016-01-22 22:33:25Z

0

another simple alternate is:

aeVehicle.MSRP = float.Parse("0" + drInvetory["MSRP"].ToString());

It will work only for positive numbers. otherwise use Microsoft.VisualBasic.Val function which is the most convenient one.

edited Jan 22, 2016 at 22:33

answered Jan 22, 2016 at 17:46

Manpreet Singh Dhillon

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