How to: Specify an out Parameter
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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 Visual C++ with OutAttribute .

The first part of this sample is a Visual C++ DLL with a type that contains a function with an out parameter.

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

This is a C# client that consumes the Visual 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
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