Re: out variable assignment - C# Discussion Boards

Re: updating error using oledbcommandbuilder

15-Jun-08 15:18

I don't see an update statement.

Christian Graus

Please read this if you don't understand the answer I've given you

"also I don't think "TranslateOneToTwoBillion OneHundredAndFortySevenMillion FourHundredAndEightyThreeThousand SixHundredAndFortySeven()" is a very good choice for a function name" - SpacixOne ( offering help to someone who really needed it ) ( spaces added for the benefit of people running at < 1280x1024 )

ginji2015-Jun-08 17:30

ginji20

15-Jun-08 17:30

d.update(ds1,"login")

actually its da.updte(ds1,"login");

this is all it need to update according to the tutorial

out variable assignment

George_George15-Jun-08 15:13

15-Jun-08 15:13

Hello everyone,

In my sample below, abcd is out parameter. I think it only reduces the value copy from input parameter of caller (Main), and it does not reduces value copy from instance returned from DateTime.Now to abcd (assignment), correct?

(in more details when we do assignment abcd = DateTime.Now, a new instance will be created, and value copied from DateTime.Now return instance, and making abcd point to the new instance?)

static void Test2(out DateTime abcd)
{
    abcd = DateTime.Now;
}

static void Main(string[] args)
{
    DateTime abcd;

    Test2(out abcd);

    return;
}

thanks in advance,
George

Christian Graus15-Jun-08 15:17

15-Jun-08 15:17

Why do you keep asking this sort of questions ? Seriously....

As previously discussed, DateTime.Now creates a new value, which is assigned to abcd. out and ref are the same in MSIL, the C# compiler enforces out.

George_George15-Jun-08 15:25

15-Jun-08 15:25

Thanks Christian,

This is not the same as the question I asked before. I just use a common scenario to ask another totally different question. Smile | :)

Christian Graus wrote:
DateTime.Now creates a new value

Yes, this is what I understand and we agree. I am not asking this.

What I am asking is how C# will treat with assignment with out variable. In my sample, at least I could think of two scenarios of how C# compiler implements this,

- making out variable pointing to the new instance returned by DateTime.Now directly;
- making a value copy from the new instance returned by DateTime.Now to another new instance, and making abcd pointing to the "another new instance".

Any ideas?

regards,
George

Christian Graus15-Jun-08 15:27

15-Jun-08 15:27

?You can always read the MSIL to answer these sort of questions. My vote is on option 1, tho.

George_George15-Jun-08 15:49

15-Jun-08 15:49

Thanks Christian!

Here is the IL code I got. I think you are correct. Using stobj will make a value copy, right? Smile | :)

.method private hidebysig static void Test2([out] valuetype [mscorlib]System.DateTime& abcd) cil managed
{
    .maxstack 8
    L_0000: nop 
    L_0001: ldarg.0 
    L_0002: call valuetype [mscorlib]System.DateTime [mscorlib]System.DateTime::get_Now()
    L_0007: stobj [mscorlib]System.DateTime
    L_000c: ret 
}

regards,
George

S. Senthil Kumar15-Jun-08 18:16

S. Senthil Kumar

15-Jun-08 18:16

George_George wrote:
making a value copy from the new instance returned by DateTime.Now to another new instance, and making abcd pointing to the "another new instance".

Why would anyone want to do it this way?

Regards
Senthil [MVP - Visual C#]
_____________________________
My Blog | My Articles | My Flickr | WinMacro

George_George15-Jun-08 18:51

15-Jun-08 18:51

Thanks Senthil,

Out variable saves value copy on stack if the value type is big. Smile | :)

Anyway, any comments or answers to my original question?

regards,
George

S. Senthil Kumar15-Jun-08 19:03

S. Senthil Kumar

15-Jun-08 19:03

George_George wrote:
Out variable saves value copy on stack if the value type is big.

Yes, it does. I was questioning your 2nd mechanism of implementing of the copy.

And yes, you got it right. out parameters are like pointers in C/C++.

void Method(int *p)
{
   int x = 20;
   *p = x;
}

void G()
{
   int y = 10;
   Method(&y); //out y
}

Regards
Senthil [MVP - Visual C#]
_____________________________
My Blog | My Articles | My Flickr | WinMacro

George_George15-Jun-08 19:14

15-Jun-08 19:14

Thanks Senthil,

1.

Sorry my English is not good. I think you mean out variable only affects function call behavior (passing pointer other than passing a value copy), not affecting assignment, correct?

2.

In my second approach, I mean we can change the pointer value of the out variable passed in, and making the pointer pointed to the instance created by DateTime.Now, so that there is no need to make another value copy from the instance created by DateTime.Now to another instance (and making abcd point to the "another instance"). Have I made myself understood?

regards,
George

S. Senthil Kumar15-Jun-08 19:34

S. Senthil Kumar

15-Jun-08 19:34

George_George wrote:
Sorry my English is not good. I think you mean out variable only affects function call behavior (passing pointer other than passing a value copy), not affecting assignment, correct?

Yes.

George_George wrote:
no need to make another value copy from the instance created by DateTime.Now to another instance (and making abcd point to the "another instance")

Yes.

Regards
Senthil [MVP - Visual C#]
_____________________________
My Blog | My Articles | My Flickr | WinMacro

George_George15-Jun-08 19:38

15-Jun-08 19:38

Thanks Senthil,

Question answered.

regards,
George

Send Keys from WebApp to WinForms

leppie15-Jun-08 19:06

leppie

15-Jun-08 19:06

George

As CG said, you are asking a lot of similar questions. Perhaps now would be a good time to start reading/studying/learning the C# and CLR Emca specifications. If it is plentiful, unambiguous information you are after (who isnt? Poke tongue | ;-P

), then that would be a good too look at. Smile | :)

Chances are better to get the correct answer there, than simply relying on word of mouth.

Cheers

leppie

xacc.ide - now with TabsToSpaces support
IronScheme - 1.0 alpha 4a out now (29 May 2008)

willybt8815-Jun-08 12:48

willybt88

15-Jun-08 12:48

Hi,

I have a requirement for a project to have a button on a webform which once pressed will switch to a running Winforms app (not in .NET) and send keys e.g. Alt S. I imagine that this is going to require ActiveX, can someone just confirm that this is the correct approach?

Thanks

Re: Send Keys from WebApp to WinForms

Christian Graus15-Jun-08 12:58

simple regular expression problem

15-Jun-08 12:58

willybt88 wrote:
to a running Winforms app (not in .NET)

This is a contradiction. WinForms is .NET. What language is your Win32 app then ?

willybt88 wrote:
I imagine that this is going to require ActiveX, can someone just confirm that this is the correct approach?

If you're going to send it to an app running on the client, ActiveX is your best bet, yes.

Stephen Po15-Jun-08 11:55

Stephen Po

15-Jun-08 11:55

hi,
I'm trying to use a regular expression to find all data following two blank lines.
this means there should be two newline formatters preceeding all data I want to find. therefore I've been trying something like:

(?<=\n\n).*

somehow I need to check the lines are indeed blank with only newline formatters and then return the text following the two new lines.
no luck though. any ideas?
thanks,
Stephen

Re: simple regular expression problem

Christian Graus15-Jun-08 12:09