.Trim() when string is empty or null

Question

I'm receiving some data from the client in the form of json. I'm writing this:

string TheText; // or whould it be better string TheText = ""; ?
TheText = ((serializer.ConvertToType<string>(dictionary["TheText"])).Trim());

If the variable that's being parsed from json comes back empty, does this code crash when I call the .Trim() method?

Thanks.

With C# 6.0 we can now use null-conditional operators, like theText?.Trim() — Santosh, Aug 06 '16 at 11:32

score 40 · Answer 1 · edited Oct 20 '22 at 02:41

40

You can use elvis operator, also known as "null-conditional-operators":

GetNullableString()?.Trim(); // returns NULL or trimmed string

More info: https://learn.microsoft.com/en-us/dotnet/csharp/language-reference/operators/null-conditional-operators

edited Oct 20 '22 at 02:41

Nicholas DiPiazza

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answered Sep 27 '16 at 13:55

TcKs

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3

https://en.wikipedia.org/wiki/Elvis_operator for those unaware of the meaning of Elvis ?: – Rob Sedgwick Jan 23 '17 at 16:07
1

This is actually called the "safe navigation operator". The Elvis operator is ?: https://en.wikipedia.org/wiki/Safe_navigation_operator – cockypup Feb 20 '19 at 21:20
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In C# it's called a null-conditional operator: https://learn.microsoft.com/en-us/dotnet/csharp/language-reference/operators/null-conditional-operators – Marc Selman Feb 28 '19 at 14:43
1

nobody cares how it's called, if it works, it works <3 – Dorin Baba Mar 24 '21 at 18:11

score 27 · Accepted Answer · answered Dec 18 '11 at 20:48

27

If the serializer returns an empty string, Trim will do nothing.

If the serializer returns null, you will get a NullReferenceException on the call to Trim.

Your code would be better written (as far as initialization is concerned) like this:

string theText = 
            ((serializer.ConvertToType<string>(dictionary["TheText"])).Trim());

There is no point in declaring and initializing the variable and the immediately assigning to it.

The following would be safest, if you don't know what the serializer might return:

string theText = ((serializer.ConvertToType<string>(dictionary["TheText"])));

if(!string.IsNullOrEmpty(theText))
{
    theText = theText.Trim();
}

answered Dec 18 '11 at 20:48

Oded

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If you've got to trim loads of fields though, this is a pain, is there no way of extending the trim method to not bother if the string is null? – JsonStatham Jun 25 '15 at 14:26
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@SelectDistinct - you can always write an extension method that does exactly that. – Oded Jun 25 '15 at 14:27
@Oded Yeah was being lazy, posted for reference for anyone else – JsonStatham Jun 25 '15 at 15:05

score 17 · Answer 3 · answered Dec 18 '11 at 20:48

17

Calling Trim() on an empty string will result in an empty string. Calling Trim() on null will throw NullReferenceException

answered Dec 18 '11 at 20:48

Armen Tsirunyan

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What's the cleanest way to check for `string.IsNullOrEmptyOrBlank`? – Paul C Feb 01 '13 at 15:11
@CodeBlend: What do you mean by blank? – Armen Tsirunyan Feb 01 '13 at 18:14
5

Aha - [String.IsNullOrWhiteSpace](http://msdn.microsoft.com/en-us/library/system.string.isnullorwhitespace.aspx) – Paul C Feb 04 '13 at 09:05

score 15 · Answer 4 · edited Jul 23 '15 at 06:12

If you have a few fields you wish to trim but your getting exceptions for those records that have nulls in certain fields, then writing a quick extension method will be the easiest method:

public static class ExtensionMethods
    {
        public static string TrimIfNotNull(this string value)
        {
            if (value != null)
            {
                return value.Trim();
            }
            return null;
        }
    }

Sample example of use:

string concatenated = String.Format("{0} {1} {2}", myObject.fieldOne.TrimIfNotNull(), myObject.fieldTwo.TrimIfNotNull(), myObject.fieldThree.TrimIfNotNull());

score 15 · Answer 5 · answered Oct 23 '18 at 08:17

Some basic techniques to check strings against null before you trim:

(mystring ?? "").Trim()
The "null coalescing operator" ?? will return the first operand. Only when this operand is null, the second operand will be returned (as a kind of default value).
The above example will return an empty string if mystring is null.
mystring?.Trim()
The "null conditional operator" ? will short cirtuit a chain of operations in dot-notation. If the operand is null, the following operations will not be executed and null will be returned.
The above example will return null if mystring is null.
if( string.IsNullOrWhiteSpace(mystring) ) { ... }
the IsNullOrWhiteSpace() method may replace trimming if you actually want to check if there is real content in mystring. It returns true if the operand is null, empty, or nothing but whitespace characters.

score 6 · Answer 6 · answered Sep 27 '16 at 13:53

As suggested in some of the comments, you may now use c# 6 Null-conditional operators with this syntax:

string TheText = (serializer.ConvertToType<string>(dictionary["TheText"]))?.Trim();

Documentation: https://msdn.microsoft.com/en-us/library/dn986595.aspx

Ry- · Answer 7 · 2019-02-28T22:17:17.960

6

No, it would not be better to initialize TheText to "". You're assigning to it right afterwards.
No, it won't crash – Trim() works just fine on an empty string. If by "empty" you mean that it can be null, then yes, it will crash; you could have null remain null with a null-conditional call:
```
string TheText =
    serializer.ConvertToType<string>(dictionary["TheText"])?.Trim();
```

edited Feb 28 '19 at 22:17

answered Dec 18 '11 at 20:47

Ry-

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score 0 · Answer 8 · answered Dec 25 '17 at 03:34

0

You can use this code as beblow

 string theText = (((serializer.ConvertToType<string>(dictionary["TheText"])))+ string.Empty).Trim();

answered Dec 25 '17 at 03:34

Trần Quốc Triển

1

Ioan Costea · Answer 9 · 2022-09-19T17:37:36.137

Recently I had to check a string if it is null, empty or whitespace using just one if condition and for that I found out that you can add "" to a null string to make it non null.

string test = GetStringFromSomeWhere(); // null
if(string.IsNullOrEmpty(test.Trim())) { return true; } // Exception

So I did this instead

string test = GetStringFromSomeWhere() + ""; // ""
if(string.IsNullOrEmpty(test.Trim())) { return true; } // true

.Trim() when string is empty or null

9 Answers9