CODEWITHSUNDEEP
c#c#-4.0
Arul
Arul

Reputation: 141

Optional parameter in c#

i am using optional parameter in the following code. but that shows error "default parameter specifiers are not permitted" anybody help me sir.

public void getno(int pvalu, string pname = "")
{

}

Upvotes: 4

Views: 7260

Answers (5)

stevehipwell
stevehipwell

Reputation: 57548

Are you compiling with the .NET 4 compiler (e.g. VS 2010) as only this compiler supports optional parameters for C#?

Personally I would overload the method rather than use optional parameters for methods that I was creating, reserving using optional parameters for use with API calls where there is a large number of default values.

Thanks to Jon Skeet for clarifying the difference between targeting .NET 4 and using the .NET 4 compiler.

Upvotes: 1

Oded
Oded

Reputation: 499302

Optional parameters have been introduced in C# 4.0 - what version are you using?

VB.NET has always had optional parameters.

You can always use overloads and method chaining to gain similar capabilities:

public void getno(int pvalu)
{
   getno(pvalue, "");
}


public void getno(int pvalu, string pname)
{

}

Upvotes: 2

Simon Steele
Simon Steele

Reputation: 11608

Optional parameters are supported in C# from version 4, make sure your project is set to compile using the C# 4 compiler.

Upvotes: 0

Jon Skeet
Jon Skeet

Reputation: 1503180

It looks like there's some misinformation in some of the answers:

  • Optional parameters were introduced into C# 4, so you must use the C# 4 compiler
  • Optional parameters have been in the framework forever, so you can target any version of the framework and still use them, so long as you're using the C# 4 compiler. It's entirely reasonable to target .NET 2 with the C# 4 compiler, and then someone referencing your library from, say, VB8 would still be able to use your optional parameters.

As others have stated, overloads are an alternative to using optional parameters if you're not using C# 4 or if you want your code to be consumed by earlier C# code. (If you build a library using C# 4 but then some C# 3 code needs to call into it, those optional parameters are effectively going to be required as far as that code is concerned.)

(As an aside, I would seriously reconsider your names... I know this is only sample code, but generally speaking prefixes like "p" for parameters are discouraged as a matter of convention, and likewise methods are generally Pascal-cased.)

Upvotes: 25

Adriaan Stander
Adriaan Stander

Reputation: 166516

Try overloading the method rather

    public void getno(int pvalu)
    {
        getno(pvalu, "");
    }

    public void getno(int pvalu, string pname)
    {

    }

Have a look at Method Usage Guidelines

See also for .Net 4 Named and Optional Arguments (C# Programming Guide)

Upvotes: 7

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