Merge pull request #2310 from mikeblome/mb-903

added Colin's wise words to topic

Author: PRMerger10

docs/dotnet/how-to-marshal-strings-using-pinvoke.md

@@ -1,7 +1,7 @@
 ---
 title: "How to: Marshal Strings Using PInvoke"
 ms.custom: "get-started-article"
-ms.date: "11/04/2016"
+ms.date: "09/09/2016"
 helpviewer_keywords: ["interop [C++], strings", "marshaling [C++], strings", "data marshaling [C++], strings", "platform invoke [C++], strings"]
 ms.assetid: bcc75733-7337-4d9b-b1e9-b95a98256088
 ---
@@ -13,6 +13,10 @@ Managed and unmanaged strings are laid out differently in memory, so passing str
 
 As with functions that use only intrinsic data types, <xref:System.Runtime.InteropServices.DllImportAttribute> is used to declare managed entry points into the native functions, but--for passing strings--instead of defining these entry points as taking C-style strings, a handle to the <xref:System.String> type can be used instead. This prompts the compiler to insert code that performs the required conversion. For each function argument in an unmanaged function that takes a string, the <xref:System.Runtime.InteropServices.MarshalAsAttribute> attribute should be used to indicate that the String object should be marshaled to the native function as a C-style string.
 
+The marshaler wraps the call to the unmanaged function in a hidden wrapper routine that pins and copies the managed string into a locally allocated string in the unmanaged context, which then is passed to the unmanaged function. When the unmanaged function returns, the wrapper either deletes the resource, or if it was on the stack, it is reclaimed when the wrapper goes out of scope. The unmanaged function is not responsible for this memory. The unmanaged code only creates and deletes memory in the heap set up by its own CRT, so there is never an issue with the marshaller using a different CRT version.
+
+If your unmanaged function returns a string, either as a return value or an out parameter, the marshaler copies it into a new managed string, and then releases the memory. For more information, see [Default Marshaling Behavior](/dotnet/framework/interop/default-marshaling-behavior) and [Marshaling Data with Platform Invoke](/dotnet/framework/interop/marshaling-data-with-platform-invoke).
+
 ## Example
 
 The following code consists of a unmanaged and a managed module. The unmanaged module is a DLL that defines a function called TakesAString that accepts a C-style ANSI string in the form of a char*. The managed module is a command-line application that imports the TakesAString function, but defines it as taking a managed System.String instead of a char\*. The <xref:System.Runtime.InteropServices.MarshalAsAttribute> attribute is used to indicate how the managed string should be marshaled when TakesAString is called.