How to set empty string when null values are passed

Question

Ok, so I am new to C Sharp and I have one function call which might send null values. I want to make sure that if its null then I should set those null as empty string. Below is what I have tried and it works but I think there must be an elegant way to achieve this.

public static Concat ()
{ 
        // imagine x = null and y = null
        Abc( x, y);
}

public static Abc ( string x , string y)
{
       // blah blah
        x = x ?? "";
        y = y ?? "";
        efg( x, y);
}

I looked into this Solution but I could not understand it. Can I do something in the Abc arguments/parameter itself. I mean

public static Abc ( string x Can I do something here , string y Can I do something here)
    {
           // blah blah
            x = x ?? "";
            y = y ?? "";
            efg( x, y);
    }

No you cannot, as defined. If you allow passing a `string` (and `null` is a valid value for a string), then null can be passed as the parameter value. Your example snippet will do the trick though: `x = x ?? "";` can be read as "set x = x if x is not null, but if it's null, set it to blank string. — SlimsGhost, Dec 09 '16 at 23:00
Or you can avoid 2 extra lines by simply having "efg (x ?? "", y ?? "");" — SlimsGhost, Dec 09 '16 at 23:02
C# does not have support for non-nullable reference types. Suppose it hadm, then your method might have looked like `public static Abc(string! x, string! y)` where the exclamation marks would mean that the compiler guarantees these are never null. For some related suggestions for future C# features, see for example [Proposal: Nullable reference types and nullability checking](https://github.com/dotnet/roslyn/issues/5032). — Jeppe Stig Nielsen, Dec 09 '16 at 23:18

score 5 · Accepted Answer · answered Dec 09 '16 at 23:01

5

I think there must be an elegant way to achieve this.

There is: the ?? operator. You found it. Good on you.

Abc ( string x Can I do something here

You can say

public static Abc(string x = "", string y = "")

and now you can call it

Abc("a", "b);
Abc("a"); // actually calls Abc("a", "")
Abc();    // actually calls Abc("", "")

but this does not change the behaviour when null is passed in. It allows you to omit an argument, not change the value of a null argument.

answered Dec 09 '16 at 23:01

Eric Lippert

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Actually the original project that I am working on had the same thing `public static Abc(string x = "", string y = "")` in it. But because of null vaues I was getting issues in my DB. Can you tell me one thing. If I keep `public static Abc(string x = "", string y = "")`. Does this make the x and y as optional parameter. I mean I can simply call `Abc()` and it would still work right? – Unbreakable Dec 09 '16 at 23:08

Bas · Answer 2 · 2016-12-12T18:10:21.670

0

Unfortunately, there is no compile time check supported natively by C# to enforce non-null values on reference types, including string.

You may provide a default value e.g. void DoSomething(string x = ""), however this does not prevent someone from overriding it with a null value.

edited Dec 12 '16 at 18:10

answered Dec 09 '16 at 23:02

Bas

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Since `string.Empty` is not a `const`, it is not a compile-time constant and cannot be used for a default value. You can define your own `const` and use that, or you can go with the literal `""`, that is `void DoSomething(string x = "")`. – Jeppe Stig Nielsen Dec 09 '16 at 23:09
My bad ! Updated the answer – Bas Dec 12 '16 at 18:10

score 0 · Answer 3 · answered Dec 09 '16 at 23:02

Minor improvement:

public static Abc ( string x , string y) => efg(x ?? "", y ?? "");

Not much different from you have already. The ? operator (as in someObject?.SomeProperty) returns the value of SomeProperty if someObject is not null. This does not apply in your example.

How to set empty string when null values are passed

3 Answers3