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 OutAttribute .


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);
a string

See also

Using C++ Interop (Implicit PInvoke)