Overview of Marshaling in C++
The new home for Visual Studio documentation is Visual Studio 2017 Documentation on docs.microsoft.com.
The latest version of this topic can be found at Overview of Marshaling in C++.
In mixed mode, you sometimes must marshal your data between native and managed types. Visual Studio 2008 introduced the marshaling library to help you marshal and convert data in a simple way.
You can use the marshaling library with or without a marshal_context Class. Some conversions require a context. Other conversions can be implemented using the marshal_as function. The following table lists the current conversions supported, whether they require a context, and what marshal file you have to include:
| From type | To type | Marshal method | Include file |
|---|---|---|---|
| System::String^ | const char * | marshal_context | marshal.h |
| const char * | System::String^ | marshal_as | marshal.h |
| char * | System::String^ | marshal_as | marshal.h |
| System::String^ | const wchar_t* | marshal_context | marshal.h |
| const wchar_t * | System::String^ | marshal_as | marshal.h |
| wchar_t * | System::String^ | marshal_as | marshal.h |
| System::IntPtr | HANDLE | marshal_as | marshal_windows.h |
| HANDLE | System::IntPtr | marshal_as | marshal_windows.h |
| System::String^ | BSTR | marshal_context | marshal_windows.h |
| BSTR | System::String^ | marshal_as | marshal.h |
| System::String^ | bstr_t | marshal_as | marshal_windows.h |
| bstr_t | System::String^ | marshal_as | marshal_windows.h |
| System::String^ | std::string | marshal_as | marshal_cppstd.h |
| std::string | System::String^ | marshal_as | marshal_cppstd.h |
| System::String^ | std::wstring | marshal_as | marshal_cppstd.h |
| std::wstring | System::String^ | marshal_as | marshal_cppstd.h |
| System::String^ | CStringT<char> | marshal_as | marshal_atl.h |
| CStringT<char> | System::String^ | marshal_as | marshal_atl.h |
| System::String^ | CStringT<wchar_t> | marshal_as | marshal_atl.h |
| CStringT<wchar_t> | System::String^ | marshal_as | marshal_atl.h |
| System::String^ | CComBSTR | marshal_as | marshal_atl.h |
| CComBSTR | System::String^ | marshal_as | marshal_atl.h |
Marshaling requires a context only when you marshal from managed to native data types and the native type you are converting to does not have a destructor for automatic clean up. The marshaling context destroys the allocated native data type in its destructor. Therefore, conversions that require a context will be valid only until the context is deleted. To save any marshaled values, you must copy the values to your own variables.
 |
|---|
If you have embedded |
The marshaling library headers are located in the include directory in the msclr subdirectory. This example shows how to include the msclr directory in an include header declaration:
#include "msclr\marshal_cppstd.h"
The marshaling library is extensible so that you can add your own marshaling types. For more information about extending the marshaling library, see How to: Extend the Marshaling Library.
In earlier versions, you could marshal data by using Platform Invoke. For more information about PInvoke, see Calling Native Functions from Managed Code.