Re: Default or optional Parameters in C# - C# Discussion Boards

Re: Default or optional Parameters in C#

PIEBALDconsult16-Dec-10 14:27

PIEBALDconsult

16-Dec-10 14:27

Done, but I've now run out of attributes -- how do you do blinking?

Re: Default or optional Parameters in C#

RaviRanjanKr15-Dec-10 17:38

RaviRanjanKr

15-Dec-10 17:38

Of-course C# 4.0 , navigate the given link to get better clarification over optional parameter.

Click Me[^]

Smile | :)

Re: Default or optional Parameters in C#

Roger Wright15-Dec-10 18:41

Roger Wright

15-Dec-10 18:41

You can accomplish a similar effect by defining several versions of the same function, each with a different signature:

public static void sample(int i, string a)
{
   bool b= true;
 //more stuff
}

public static void sample(int i, bool b)
{
   string s = string.Empty;
 //more stuff
}

public static void sample(string a, bool b)
{
   int i = 100;
 //more stuff
}

etc...

If I remember my reading correctly, at run time the calling statement will be matched to the version with matching parameters, and the function will fill in the missing values with the predefined defaults.

Of course, I may be a complete idiot - I'm fairly new to C#. But it's what I would try if I really needed to do this. Smile | :)

Will Rogers never met me.

Re: Default or optional Parameters in C#

Gary Wheeler16-Dec-10 0:47

Gary Wheeler

16-Dec-10 0:47

I usually implement that pattern as follows in C# 3.5:

public static void sample(int i, string a)
{
   _sample(i,false,true,a);
}
public static void sample(int i, bool b)
    _sample(i,false,b,string.Empty);
}
public static void sample(string a, bool b)
{
   _sample(100,false,b,a);
}
private static void _sample(int i,bool a,bool b,string a_string)
{
   // implement 'sample' operation
}

Software Zen: delete this;

Re: Default or optional Parameters in C#

ely_bob20-Dec-10 9:13

ely_bob

20-Dec-10 9:13

This is what I use, however I'll admit I feel it slopifies the code base.... D'Oh! | :doh:

I'd blame it on the Brain farts.. But let's be honest, it really is more like a Methane factory between my ears some days then it is anything else...

-----

"The conversations he was having with himself were becoming ominous."-.. On the radio...

Re: Default or optional Parameters in C#

deepakshukla7915-Dec-10 19:36

deepakshukla79

15-Dec-10 19:36

You can use optional parameter .
you can this by this way
class Program
{
static void Main(string[] args)
{
Console.WriteLine(Sum(1, 2, 3).ToString());
Console.WriteLine(Sum( 2, 3).ToString());
Console.ReadLine();
}

static int Sum(params int[] li)
{
int sum=0;
for ( int i = 0 ; i < li.Length ; i++ )
{
sum+=li[i];
}
return sum;
}
}

Re: Default or optional Parameters in C#

Hiren solanki15-Dec-10 19:58

Hiren solanki

15-Dec-10 19:58

You've provided a way which can be only applicable to Integer, Try to expand it for all type of object passed in method.

Like instead of receiving data only in a array of int[], Receive it in object[]. and further check of every item in array whether it's bool,string,object of custom class,float,decimal.

That would be quite cumbersome, optional parameter is the good way , I guess.

Regards,
Hiren.

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Re: Default or optional Parameters in C#

Spectre_00116-Dec-10 1:33

Spectre_001

16-Dec-10 1:33

Not exactly elegant but...

public static void sample(int i, string s, bool b)
{
    if (i == default(int)) { i = 100; }
    if (s == default(string)) { s = string.Empty; }
    if (b == default(bool)) { b = true; }

    // The rest of your method...
}

Works in .NET Framework 3.5.

Kevin Rucker, Application Programmer
QSS Group, Inc.
United States Coast Guard OSC
Kevin.D.Rucker@uscg.mil

"Programming is an art form that fights back." -- Chad Hower

Re: Default or optional Parameters in C#

djdanlib16-Dec-10 5:44

djdanlib

16-Dec-10 5:44

Wait, how does that even work? I've never even heard of something like that. I am intrigued.

Is this what you're doing? http://msdn.microsoft.com/en-us/library/xwth0h0d%28v=VS.80%29.aspx[^]

Re: Default or optional Parameters in C#

Spectre_00116-Dec-10 5:53

Spectre_001

16-Dec-10 5:53

Yes, it just returns the framework's default value for the type specified.

Kevin Rucker, Application Programmer
QSS Group, Inc.
United States Coast Guard OSC
Kevin.D.Rucker@uscg.mil

"Programming is an art form that fights back." -- Chad Hower

Re: Default or optional Parameters in C#

PIEBALDconsult16-Dec-10 14:30

PIEBALDconsult

16-Dec-10 14:30

So, then, how would I specify 0, null, and false (?) when I want to?

Re: Default or optional Parameters in C#

Spectre_00120-Dec-10 2:36

Spectre_001

20-Dec-10 2:36

See the answer I posted to StephenPhillips.

Kevin Rucker, Application Programmer
QSS Group, Inc.
United States Coast Guard OSC
Kevin.D.Rucker@uscg.mil

"Programming is an art form that fights back." -- Chad Hower

Re: Default or optional Parameters in C#

StephenPhillips17-Dec-10 2:32

StephenPhillips

17-Dec-10 2:32

Hmm, surely that misses the advantage of giving optional parameters, i.e. you can call the function without specifying all the input - using this form means you still need to give three values, or it doesn't match the function. Also, in this example, it's impossible to supply 'false' for the third value; false is the default value for a bool, so it would always become true.

Re: Default or optional Parameters in C#

Spectre_00120-Dec-10 2:36

Spectre_001

20-Dec-10 2:36

You're absolutely correct, the only way to truly emulate optional parameters like in VB would be to use overloads of the method like this:

public static void sample(int i, string s, bool b)
{
    // Do work here
}

public static void sample(int i)
{
    sample(i, string.Empty, true);
}

public static void sample(int i, string s)
{
    sample(i, s, true);
}

public static void sample(int i, bool b)
{
    sample(i, string.Empty, b);
}

public static void sample(string s)
{
    sample(100, s, true);
}

public static void sample(string s, bool b)
{
    sample(100, s, b);
}

public static void sample (bool b)
{
    sample(100, string.Empty, b);
}

public static void sample()
{
    sample(100, string.Empty, true);
}

Which swiftly becomes unweildy once you get past three parameters.

Kevin Rucker, Application Programmer
QSS Group, Inc.
United States Coast Guard OSC
Kevin.D.Rucker@uscg.mil

"Programming is an art form that fights back." -- Chad Hower

Re: Default or optional Parameters in C#

Hari Om Prakash Sharma16-Dec-10 3:03

Hari Om Prakash Sharma

16-Dec-10 3:03

visual studio 2010

First and the Foremost: FIGHT TO WIN

Re: Default or optional Parameters in C#

hground16-Dec-10 3:30

hground

16-Dec-10 3:30

VB .NET has had optional parameters for some time Smile | :)

Looks like it took C# a while to catch up Smile | :)

(Yeah - I know! I shouldn't throw rocks at hornet's nests,
but sometimes you just can't resist!)

Re: Default or optional Parameters in C#

jlafay16-Dec-10 4:09

jlafay

16-Dec-10 4:09

That's possible in C# 4, and the same syntax applies.

-jeff

Re: Default or optional Parameters in C#

grgran16-Dec-10 4:58

grgran

16-Dec-10 4:58

As already pointed out, optional, default and named parameters are available in .NET 4.0
Interestingly, if you do use them the code analysis tool slaps your hand about it, requesting that you create overloads with the defaults set in method.
G

Re: Default or optional Parameters in C#

PIEBALDconsult16-Dec-10 14:26

PIEBALDconsult

16-Dec-10 14:26

grgran wrote:
.NET 4.0

C# 4 dagnabit!!!

Re: Default or optional Parameters in C#

Paladin200016-Dec-10 5:08

Paladin2000

16-Dec-10 5:08

No, you can't set default values. But you can use an overload to accomplish something similar.

public static void sample(int i, string s, bool b)
{
///Something 
}

public static void sample()
{
  sample(100, string.Empty, true);
}

public static void sample(int i)
{
  sample(i, string.Empty, true);
}

///Etc...

Re: Default or optional Parameters in C#

Jeff Connelly17-Dec-10 5:57

Jeff Connelly

17-Dec-10 5:57

Yes, the C# lost that feature from "primitive" C++. You get it back with interest in C# 4.0 - not only can you provide default parameter values, you can also name your parameters and provide them in any order you want.

For example, in C++ you had to order your function parameters correctly, so that the ones with default values came at the end.

void foo(int i = 1, int j = 0, int k)

This didn't work, because what does the call foo(1, 2) mean?

In C# 4.0, you can do that.

foo(k: 0, j: 1)

So add "named" parameters (arguments) to the feature, which was not available in C++.

Hashtable within Hashtable

michael_jhons15-Dec-10 5:47

michael_jhons

15-Dec-10 5:47

hello everybody,

i'm retreiving data(API) with JSON format and i'm parsing it inside a hashtable,
it seems like some specific keys have a value= hashtable(or arraylist!)
below is how i'm extractin the the first layer value

foreach (object objResult in jsonResults)
           {
               Hashtable jsonResult = (Hashtable)objResult;
               dt.Rows.Add(jsonResult["city"].ToString(), jsonResult["reviews"].ToString(), jsonResult["avg_rating"].ToString(), jsonResult["rating_img_url"].ToString());
           }

the problem is where the values are equal to arraylist i'm not able to extract them

Is there any way to extract the second layer keys and values? (btw i'm very new to hashtables and arraylists)

Thank you in advance

Re: Hashtable within Hashtable

Abhinav S15-Dec-10 5:56

Abhinav S

15-Dec-10 5:56

Yes. You need to access the second level values using their keys and then putting them into your string.

e.g.

Dictionary x = (Dictionary)jsonResult["reviews"];<br />
string res = x["mySecondLevelReviews"].ToString();

The funniest thing about this particular signature is that by the time you realise it doesn't say anything it's too late to stop reading it.

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Re: Hashtable within Hashtable

michael_jhons15-Dec-10 10:12

michael_jhons

15-Dec-10 10:12

thank you Abhinav for your help,

i did apply what you've suggested withoout any luck,
i just want to highlight that jsonResult["reviews"].GetType()= Arraylist

what should i set the the type of keys and values in Dictionary
Dictionary<tkey,tvalue> ?

thank you again for your concern

Re: Hashtable within Hashtable

_Erik_15-Dec-10 5:59

_Erik_

15-Dec-10 5:59

Since your data seems to be in JSON format, you might want to use JsonReaderWriterFactory[^] class. It will become much easier to parse.

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