marshal String^ to string. Get an error with marshal.h

Question

I have both of these in my class

#include <msclr/marshal.h>
#include <msclr/marshal_cppstd.h>

and I have

using namespace msclr::interop;

I am using it to marshal String^ to string. Here is one example.

string ProgReleaseType = marshal_as<std::string>(CurrentSubKey->GetValue("ReleaseType", NULL)->ToString());

When I build, I get this error.

Error   53  error C4996: msclr::interop::error_reporting_helper<_To_Type,_From_Type,false>::marshal_as': This conversion is not supported by the library or the header file needed for this conversion is not included.  Please refer to the documentation on 'How to: Extend the Marshaling Library' for adding your own marshaling method.    C:\Program Files (x86)\Microsoft Visual Studio 12.0\VC\include\msclr\marshal.h  237

When I go into the marshal.h and read through line 237 is says to please use a marshal_context. I thought I was. I don't get what it doesn't like.

Answer 1

Use a marshal context:

 msclr::interop::marshal_context context;

string ProgReleaseType = context.marshal_as<std::string>(CurrentSubKey->GetValue("ReleaseType", NULL)->ToString());

Answer 2

I'm unable to reproduce this error as described. That is the error I get if I include msclr\marshal.h but not msclr\marshal_cppstd.h. Double-check you're including it, or perhaps include it explicitly as the very first line in your cpp file.

Here's my test application:

#include <msclr\marshal.h>
#include <msclr\marshal_cppstd.h>

using namespace msclr::interop;
using namespace System;
using namespace System::Diagnostics;

int main(array<System::String ^> ^args)
{
    String^ str = "Something";

    std::string stdstr = marshal_as<std::string>(str);

    stdstr[4] = '-';

    // Convert back to managed for printing.
    Debug::WriteLine(marshal_as<String^>(stdstr));

    return 0;
}

Output:

Some-hing

Answer 3

I hope this answer will help you.

1. Add header

    #include <msclr\marshal_cppstd.h>
   

2. Here is sample code for String^ to string (standard string)

     String^ str ="Sample string";
     msclr::interop::marshal_as<std::string>(str)