c# Null-conditional Operator

Question

I am trying to use the Null-conditional Operator (?) but I am not quite sure where exactly to put it separators.Contains(textLine[(index - 1)]). I want to say "If (textLine[(index - 1)]) isn't null proceed". Some help?

Do you mean "if the expression is not null, call the Contains method, otherwise don't"? — Lasse V. Karlsen
– Lasse V. Karlsen, Commented Jan 7, 2017 at 18:08
Unfortunately this can't be done, you need to use an if-statement. — Lasse V. Karlsen
– Lasse V. Karlsen, Commented Jan 7, 2017 at 18:11
operators are for expressions, flow of control are for statements. You need flow of control (eg if) — Hogan
– Hogan, Commented Jan 7, 2017 at 18:12

Orel Eraki · Accepted Answer · 2017-01-07 18:16:55Z

5

This is not the way Null-conditional Operators works.

Null-conditional Operators, only returns null instead of an exception, if one of the parents marked with prefix of ? is == null

Example:

var g1 = parent?.child?.child?.child; 
if (g1 != null) // TODO

What you need, is a simple IF condition

if (!string.IsNullOrEmpty(textLine))
{
    // Work here
}

answered Jan 7, 2017 at 18:16

Orel Eraki

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Rabid Penguin · Accepted Answer · 2017-01-08 20:47:40Z

1

If you mean to not call the contains method if the value in your array is null then you have to check it first.

// requires possible bounds checking
char? test = textLine?[index-1];
if (test != null && separaters.Contains(test.Value))

Using linq:

// does not require bounds checking
char test = textLine?.Skip(index-1).FirstOrDefault() ?? default(char);
if (test != default(char) && separaters.Contains(test))

edited Jan 8, 2017 at 20:47

answered Jan 7, 2017 at 18:20

Rabid Penguin

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10 Comments

M.kazem Akhgary Over a year ago

first of all char can never be null. did you mean to write textLine?[index-1]; instead?

user7388546 Over a year ago

yea that's what i realised now @M.kazemAkhgary

Rabid Penguin Over a year ago

That's correct i was unsure if he meant textLine would be null or the value in the array could be null

user7388546 Over a year ago

I am getting an out of range exception

Rabid Penguin Over a year ago

You could use linq. char test = textLine?.Skip(index-1).FirstOrDefault() ?? default(char). Then test against default(char)

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Pluriscient · Accepted Answer · 2017-01-07 18:14:13Z

1

The second example of the MSDN Docs should answer your question:

 Customer first = customers?[0];  // null if customers is null

answered Jan 7, 2017 at 18:14

Pluriscient

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