how-to-specify-an-out-parameter.md

description	Learn more about: How to: Specify an out parameter
title	How to: Specify an out parameter
ms.custom	get-started-article
ms.date	11/04/2016
helpviewer_keywords	function parameters out parameters
ms.assetid	02862448-603c-4e9d-a5c5-b45fe38446e3

How to: Specify an out parameter

This sample shows how to specify that a function parameter is an out parameter, and how to call that function from a C# program.

An out parameter is specified in C++ by using xref:System.Runtime.InteropServices.OutAttribute .

Example

The first part of this sample creates a C++ DLL. It defines a type that contains a function with an out parameter.

// cpp_out_param.cpp
// compile with: /LD /clr
using namespace System;
public value struct TestStruct {
   static void Test([Runtime::InteropServices::Out] String^ %s) {
      s = "a string";
   }
};

This source file is a C# client that consumes the C++ component created in the previous example.

// cpp_out_param_2.cs
// compile with: /reference:cpp_out_param.dll
using System;
class TestClass {
   public static void Main() {
      String t;
      TestStruct.Test(out t);
      System.Console.WriteLine(t);
   }
}

a string

See also

Using C++ Interop (Implicit PInvoke)