Problem with parameter

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Martin - 18 May 2005 17:52 GMT

Hi all,

I have a Webservice in C#, I call this webservice function with a parameter
as String object (named pMessage)
In the function the String object pMessage will be set to corresp. messsage.
But in client program, this parameter is unchanged. Why? How can I do?

The code is following:
[Web ...]
public bool xxx(String pMessage)
{
if (..)
pMessage = " 111";
else
pMessage = " 222";
}

Client:

String sMsg = "";
webservice1.xxx(sMsg);
MessageBox.show(sMsg);

Thanks
Martin

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Chad Z. Hower aka Kudzu - 18 May 2005 18:50 GMT

> messsage. But in client program, this parameter is unchanged. Why? How
> can I do?
>
> The code is following:
> [Web ...]
> public bool xxx(String pMessage)

Of course, this is a by VALUE reference, not a byref.

--
Chad Z. Hower (a.k.a. Kudzu) - http://www.hower.org/Kudzu/
"Programming is an art form that fights back"

Blog: http://blogs.atozed.com/kudzu

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Martin - 18 May 2005 19:19 GMT

Hi,
what do you think about?

I think, when I pass a String Object to a function, the function can change
its value, properties, these changes are made to the original object.

I have tried with "public bool xxx( ref String pMessage)", But it is the
same result.
I think, in this case, byref means, the function can change the reference to
another String Object (in C++ is this corresp. to pointer, point to another
object?)

Otherwise, I understood, byval, in, out have meaning only with the primitive
type.

> > messsage. But in client program, this parameter is unchanged. Why? How
> > can I do?
[quoted text clipped - 10 lines]
>
> Blog: http://blogs.atozed.com/kudzu

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Chad Z. Hower aka Kudzu - 19 May 2005 05:45 GMT

> I think, when I pass a String Object to a function, the function can
> change its value, properties, these changes are made to the original
> object.

No.

private void Test(string x) {
x = "Hello";
}

private void button1_Click_1(object sender, System.EventArgs e) {
string y = "Bye";
Test(y);
button1.Text = y;
}

button1 says Byte, not Hello.

This makes it say Bye:

private void Test(ref string x) {
x = "Hello";
}

private void button1_Click_1(object sender, System.EventArgs e) {
string y = "Bye";
Test(ref y);
button1.Text = y;
}

> I have tried with "public bool xxx( ref String pMessage)", But it is the
> same result.

Webservices AFAIK dont support ref parameters. I think they support out
parameters though, you can try:

bool(string InString, out string OutString);

> I think, in this case, byref means, the function can change the
> reference to another String Object (in C++ is this corresp. to pointer,
> point to another object?)

Essentially.

> Otherwise, I understood, byval, in, out have meaning only with the
> primitive type.

No, its can effect objects too. Strings are immutable, so any change you
make makes a NEW string. So if you pass the object byval, there are now two
objects, and the first is not the same as the reference holder to the new
one.

--
Chad Z. Hower (a.k.a. Kudzu) - http://www.hower.org/Kudzu/
"Programming is an art form that fights back"

Blog: http://blogs.atozed.com/kudzu

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Martin - 19 May 2005 09:12 GMT

Thanks

> Webservices AFAIK dont support ref parameters. I think they support out
> parameters though, you can try:
>
> bool(string InString, out string OutString);

I had tried this way, before I asked newsgroup. But I call this method
false:
bool login(..., out string sMessage)

login(..., sMessage);

Now I wrote:
login(..., out sMessage);

Thanks again

> > I think, when I pass a String Object to a function, the function can
> > change its value, properties, these changes are made to the original
[quoted text clipped - 53 lines]
>
> Blog: http://blogs.atozed.com/kudzu

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Ravichandran J.V. - 19 May 2005 08:25 GMT

you need a lvalue to call a function and anyway, change the return type of
the webservice method to string so as to receive a string from the web
service.

with regards,

J.v.

> Hi all,
>
[quoted text clipped - 21 lines]
> Thanks
> Martin

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