How to turn System::String^ into std::string?

So i work in clr, creating .net dll in visual c++.

I tru such code:

 static bool InitFile(System::String^ fileName, System::String^ container)
{
    return enc.InitFile(std::string(fileName), std::string(container));
}

having encoder that normaly resives std::string. but here the compiler (visual studio) gives me C2664 error if I strip out arguments from std::string and C2440 which is in general the same. VS tells me that it just can not to convert System::String^ into std::string.

So I am sad... what shall I do to turn System::String^ into std::string?

Update:

Now with your help I have such code

#include <msclr\marshal.h>
#include <stdlib.h>
#include <string.h>
using namespace msclr::interop;
namespace NSSTW
{
  public ref class CFEW
  {
 public:
     CFEW() {}

     static System::String^ echo(System::String^ stringToReturn)
    {
        return stringToReturn;  
    }

     static bool InitFile(System::String^ fileName, System::String^ container)
    {   
        std::s开发者_JS百科tring sys_fileName = marshal_as<std::string>(fileName);;
        std::string sys_container = marshal_as<std::string>(container);;
        return enc.InitFile(sys_fileName, sys_container);
    }
...

but when I try to compile it gives me C4996

error C4996: 'msclr::interop::error_reporting_helper<_To_Type,_From_Type>::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.

what to do?

If you're using VS2008 or newer, you can do this very simply with the automatic marshaling added to C++. For example, you can convert from System::String^ to std::string via marshal_as:

System::String^ clrString = "CLR string";
std::string stdString = marshal_as<std::string>(clrString);

This is the same marshaling used for P/Invoke calls.

From the article How to convert System::String^ to std::string or std::wstring on MSDN:

void MarshalString (String ^ s, string& os) 
{
    using namespace Runtime::InteropServices;
    const char* chars = 
      (const char*)(Marshal::StringToHGlobalAnsi(s)).ToPointer();
    os = chars;
    Marshal::FreeHGlobal(IntPtr((void*)chars));
}

Usage:

std::string a;
System::String^ yourString = gcnew System::String("Foo");
MarshalString(yourString, a);
std::cout << a << std::endl; // Prints "Foo"

You need to include marshal_cppstd.h to convert String^ to std::string.

You don't mention if you're concerned at all about non-ascii characters. If you need unicode (and if not, why not!?), there is a marshal_as which returns a std::wstring.

If you're using utf8, you'll have to roll your own. You can use a simple loop:

System::String^ s = ...;
std::string utf8; 
for each( System::Char c in s )
    // append encoding of c to "utf8";

How to convert from System::String* to Char* in Visual C++

Once you have a char*, simply pass it to the std::string constructor.