Writing Nullable value with BinaryWriter

Question

I want to write a nullable string to file using BinaryWriter and this code:

  BinaryWriter writer = new BinaryWriter(st);
  String? s;
  if(s!=null){
        writer.Write(s);
    }

but this error occurs:

The type 'string' must be a non-nullable value type in order to use it as parameter 'T' in the generic type or method 'System.Nullable'

How can I solve this problem?

Duplicate of http://stackoverflow.com/q/187406/700972 – torrential coding Apr 19 '13 at 14:56 — torrential coding, Apr 19 '13 at 14:56
oh, silly question I forgotten that! – Majid Apr 19 '13 at 15:12 — Majid, Apr 19 '13 at 15:12

score 4 · Accepted Answer · answered Apr 19 '13 at 14:56

4

Strings can always be null, you don't need to try and make it nullable as they're not value types. Just remove the ? That makes it nullable to fix it.

answered Apr 19 '13 at 14:56

Ian

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score 2 · Answer 2 · answered Apr 19 '13 at 14:57

2

Strings are already nullable in C#.NET, they're a reference type with syntactic sugar around them to make them easier to use. You can't make a nullable double nullable, the universe would collapse.

answered Apr 19 '13 at 14:57

Jeff Watkins

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score 2 · Answer 3 · answered Apr 19 '13 at 14:58

2

According to MSDN documentation, we can see that Nullable type can be used only with structs:

[SerializableAttribute]
public struct Nullable<T>
where T : struct

p.s. see also Constraints on Type Parameters.

answered Apr 19 '13 at 14:58

Dzmitry Martavoi

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score 1 · Answer 4 · answered Apr 19 '13 at 14:56

1

String is a reference type. It can not be nullable.
public struct Nullable<T> where T : struct, new()

answered Apr 19 '13 at 14:56

Vladimir

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Writing Nullable value with BinaryWriter

4 Answers4