Hello,

I've got what I'm sure are some dumb questions. I've got some existing C++ 
code that I want to move to a C++/CLI assembly to make it easier to use in a 
..NET app as well as continuing to use it in an existing C++ app. It's simple 
code, but I'm not sure if I'm setting up my function definitions properly. 

If I've got a function that takes a string would this be correct:

void PassInString(String^% string1);

What about when I need to return a string from a function. Could someone 
show me a simple code snippet? I've tried some things, but I keep getting 
errors.

Thanks for any help, I really appreciate it.

Thanks,
Nick

>If I've got a function that takes a string would this be correct:
>
>void PassInString(String^% string1);


You only need String ^ string1


>What about when I need to return a string from a function. Could someone 
>show me a simple code snippet? I've tried some things, but I keep getting 
>errors.


String ^ fn()
{
String ^ s = gcnew String( "Whatever" );
return s;
}

Dave

"David Lowndes" <DavidL@example.invalid> wrote in message 
news:nru6c3d1gk90d6at1tbo6llj8s2gfsdntj@4ax.com...

> >If I've got a function that takes a string would this be correct:
>>
>>void PassInString(String^% string1);


This is equivalent to C#

void PassInString(ref String string1) { ... }
or
void PassInString(out String string1) { ... }

You would use System.Runtime.InteropServices.OutAttribute to specify the 
latter.


>
> You only need String ^ string1


This is normal pass-by-value of a handle to an immutable string -- the 
caller's copy cannot be changed.


>
>>What about when I need to return a string from a function. Could someone
>>show me a simple code snippet? I've tried some things, but I keep getting
>>errors.
>
> String ^ fn()
> {
> String ^ s = gcnew String( "Whatever" );
> return s;
> }
>
> Dave 

Thanks Dave, I really appreciate it. Out of curiousity, what does the % do? 
Anything?

Thanks,
Nick

>Thanks Dave, I really appreciate it. Out of curiousity, what does the % do? 
>Anything?


Oh yes. It signifies a "tracking reference" - have a look on MSDN for
the details.

Dave

Hi,

I think "Ben Voigt [C++ MVP]" has explained the meaning of "%" in function 
call. It means passing the CLR types by reference with tracking references. 

Actually, there are 2 ways to return the result to the caller: 
1. Through the return value.
2. Through the parameter by reference.(Using "%" in function parameter)

The code below demonstrates both 2 approaches:

void fnRef(String^% str)
{
	str =  str + "Whatever";
}

String ^ fn(String^ str)
{
	String ^ s = gcnew String( str + "Whatever" );
	return s;
}

int main(array<System::String ^> ^args)
{
	String ^ str="abc";
	String ^ result = fn(str);
                Console::WriteLine(result);


	fnRef(result);
                Console::WriteLine(result);
                return 0;
}

Please refer to the link below for several usage of "%" in C++/CLI:
http://msdn2.microsoft.com/en-us/library/8903062a(VS.80).aspx

Hope this helps.

Best regards,
Jeffrey Tan
Microsoft Online Community Support
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