Need declare a field corresponding a property in c#?

Question

What is the difference between

private string someText;

public string SomeText
{
    get;
    set;
}

and

public string SomeText
{
    get;
    set;
}

I'm not a C#-expert but it seems like the first example doesn't really use the private string. You could probably learn a lot by reading the official [C# Programming Guide about properties](http://msdn.microsoft.com/en-us/library/w86s7x04.aspx) — Simon Forsberg, Oct 16 '13 at 00:41

score 3 · Accepted Answer · answered Oct 16 '13 at 00:42

3

nothing at all, your private member is not being used.

The compiler will compile

public string SomeText
{
     get;
     set;
}

to the equivalent of

private string _someText;

public string SomeText
{
   get { return _someText; }
   set { _someText = value; }
}

answered Oct 16 '13 at 00:42

Rhys Bevilaqua

2,102
17
20

I think an important point here is that the field is not actually called `_someText`, its name is something that you can't write in your code. – svick Oct 16 '13 at 01:05
@svick yep, but I figured it was better to show correct naming standards and say "equivalent" than to go hunting for the exact code it actually generates `[CompilerGenerated]private string k__BackingField;` [see here](http://stackoverflow.com/questions/1277018/c-sharp-3-0-automatic-properties-what-would-be-the-name-of-private-variable-c/1277082#1277082) – Rhys Bevilaqua Oct 23 '13 at 01:59

NDJ · Answer 2 · 2013-10-16T00:52:43.883

You do realise that your question is comparing two equal things? (

public string SomeText
{
    get;
    set;
}

)

I'm thinking what your question really is - is what is the difference between

private string someText;

public string SomeText
{
    get
     {
       return someText;
     }

    set 
     {
      someText = value;
     }
}

and :

public string SomeText
{
    get;
    set;
}

To which the answer is, in the 2nd example the backing fields still exist but are created for you - and you have no influence over the setting/getting; whereas in the first example you can put other checks in to make sure it's a valid value being set, etc.

wlz · Answer 3 · 2013-10-16T00:52:50.423

I think maybe you want to know the difference between

public class Test1
{
    private string _text;
    public string Text
    {
        get { return _text; }
        set { _text = value; }
    }
}

and

 public class Test2
{
    public string Text
    {
        get;
        set;
    }
}

If you disassemble these two classes into CIL , you will find it's almost the same except in the second case , the field was a auto generated one .

First case:

.property instance string Text
{
    .get instance string Syner.Test1::get_Text()
    .set instance void Syner.Test1::set_Text(string)
}


.field private string _text

Second case:

 .property instance string Text
{
    .get instance string Syner.Test2::get_Text()
    .set instance void Syner.Test2::set_Text(string)
}


.field private string <Text>k__BackingField
{
    .custom instance void [mscorlib]System.Runtime.CompilerServices.CompilerGeneratedAttribute::.ctor()
}

Evan Trimboli · Answer 4 · 2013-10-16T01:09:41.723

The second is just syntactic sugar for:

private string someText;

public string SomeText
{
    get { return someText; }
    set { someText = value; }
}

The second automatically handles the variable creation etc for you behind the scenes. In your first example, the private variable someText is never read/modified, it's just a class level variable that does nothing.

The reason you might want to use the first is if you need to do something more complicated in the getter/setter. For example you might want to check if something is initialized in the getter. Or you might want to validate the value in the setter.

You're saying that as if in the first example, the field was actually used. — svick, Oct 16 '13 at 01:06

Need declare a field corresponding a property in c#?

4 Answers4