In C++/CLI, how do I declare and call a function with an 'out' parameter?
I have a function which parses one string into two strings. In C# I would declare it like this:
void ParseQuery(string toParse, out string search, out string sort)
{
...
}
and I'd call it like this:
string searchOutput, sortOutput;
ParseQuery(userInput, out searchOutput, out sortOutput);
The current project has to be done in C++/CLI. I've tried
using System::Runtime::InteropServices;
...
void ParseQuery(String ^ toParse, [Out] String^ search, [Out] String^ sort)
{
...
}
but if I call it like this:
String ^ searchOutput, ^ sortOutput;
ParseQuery(userInput, [Out] searchOutput, [Out] sortOutput);
I get a compiler error, and if I call it like this:
String ^ searchOutput, ^ sortOutput;
ParseQuery(userInput, searchOutput, sortOutput);
then I get an error at runtime. How should I declare and call my function?
C++/CLI itself doesn't support a real 'out' argument, but you can mark a reference as an out argument to make other languages see it as a real out argument.
You can do this for reference types as:
void ReturnString([Out] String^% value)
{
value = "Returned via out parameter";
}
// Called as
String^ result;
ReturnString(result);
And for value types as:
void ReturnInt([Out] int% value)
{
value = 32;
}
// Called as
int result;
ReturnInt(result);
The % makes it a 'ref' parameter and the OutAttribute marks that it is only used for output values.
Using Visual Studio 2008, this works and solved a major problem at my job. Thanks!
// header
// Use namespace for Out-attribute.
using namespace System::Runtime::InteropServices;
namespace VHT_QMCLInterface {
public ref class Client
{
public:
Client();
void ReturnInteger( int a, int b, [Out]int %c);
void ReturnString( int a, int b, [Out]String^ %c);
}
}
// cpp
namespace VHT_QMCLInterface {
Client::Client()
{
}
void Client::ReturnInteger( int a, int b, [Out]int %c)
{
c = a + b;
}
void Client::ReturnString( int a, int b, [Out]String^ %c)
{
c = String::Format( "{0}", a + b);
}
}
// cs
namespace TestQMCLInterface
{
class Program
{
VHT_QMCLInterface.Client m_Client = new VHT_QMCLInterface.Client();
static void Main(string[] args)
{
Program l_Program = new Program();
l_Program.DoReturnInt();
l_Program.DoReturnString();
Console.ReadKey();
}
void DoReturnInt()
{
int x = 10;
int y = 20;
int z = 0;
m_Client.ReturnInteger( x, y, out z);
Console.WriteLine("\nReturnInteger: {0} + {1} = {2}", x, y, z);
}
void DoReturnString()
{
int x = 10;
int y = 20;
String z = "xxxx";
m_Client.ReturnString(x, y, out z);
Console.WriteLine("\nReturnString: {0} + {1} = '{2}'", x, y, z);
}
}
}