C++/CLI Converting from System::String^ to std::st

Question

Can someone please post a simple code that would convert,

System::String^

To,

C++ std::string

I.e., I just want to assign the value of,

String^ originalString;

To,

std::string newString;

Answer 1

You can easily do this as follows

#include <msclr/marshal_cppstd.h>

System::String^ xyz="Hi boys"; 

std::string converted_xyz=msclr::interop::marshal_as< std::string >( xyz);

Answer 2

// I used VS2012 to write below code-- convert_system_string to Standard_Sting

        #include "stdafx.h"
        #include <iostream>
        #include <string> 

        using namespace System;
        using namespace Runtime::InteropServices; 


        void MarshalString ( String^ s, std::string& outputstring )
        {  
           const char* kPtoC =  (const char*) (Marshal::StringToHGlobalAnsi(s)).ToPointer();                                                        
           outputstring = kPtoC;  
           Marshal::FreeHGlobal(IntPtr((void*)kPtoC));  
        }   

        int _tmain(int argc, _TCHAR* argv[])
        {
             std::string strNativeString;  
             String ^ strManagedString = "Temp";

             MarshalString(strManagedString, strNativeString);  
             std::cout << strNativeString << std::endl; 

             return 0;
        }

Answer 3

C# uses the UTF16 format for its strings.
So, besides just converting the types, you should also be conscious about the string's actual format.

When compiling for Multi-byte Character set Visual Studio and the Win API assumes UTF8 (Actually windows encoding which is Windows-28591 ).
When compiling for Unicode Character set Visual studio and the Win API assume UTF16.

So, you must convert the string from UTF16 to UTF8 format as well, and not just convert to std::string.
This will become necessary when working with multi-character formats like some non-latin languages.

The idea is to decide that std::wstring always represents UTF16.
And std::string always represents UTF8.

This isn't enforced by the compiler, it's more of a good policy to have.

#include "stdafx.h"
#include <string>
#include <codecvt>
#include <msclr\marshal_cppstd.h>

using namespace System;

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

    msclr::interop::marshal_context context;

    //Actual format is UTF16, so represent as wstring
    std::wstring utf16NativeString = context.marshal_as<std::wstring>(managedString); 

    //C++11 format converter
    std::wstring_convert<std::codecvt_utf8_utf16<wchar_t>> convert;

    //convert to UTF8 and std::string
    std::string utf8NativeString = convert.to_bytes(utf16NativeString);

    return 0;
}

Or have it in a more compact syntax:

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

    msclr::interop::marshal_context context;
    std::wstring_convert<std::codecvt_utf8_utf16<wchar_t>> convert;

    std::string utf8NativeString = convert.to_bytes(context.marshal_as<std::wstring>(managedString));

    return 0;
}

Answer 4

I spent hours trying to convert a windows form listbox ToString value to a standard string so that I could use it with fstream to output to a txt file. My Visual Studio didn't come with marshal header files which several answers I found said to use. After so much trial and error I finally found a solution to the problem that just uses System::Runtime::InteropServices:

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));
}

//this is the code to use the function:
scheduleBox->SetSelected(0,true);
string a = "test";
String ^ c = gcnew String(scheduleBox->SelectedItem->ToString());
MarshalString(c, a);
filestream << a;

And here is the MSDN page with the example: http://msdn.microsoft.com/en-us/library/1b4az623(v=vs.80).aspx

I know it's a pretty simple solution but this took me HOURS of troubleshooting and visiting several forums to finally find something that worked.

Answer 5

Check out System::Runtime::InteropServices::Marshal::StringToCoTaskMemUni() and its friends.

Sorry can't post code now; I don't have VS on this machine to check it compiles before posting.

Answer 6

I found an easy way to get a std::string from a String^ is to use sprintf().

char cStr[50] = { 0 };
String^ clrString = "Hello";
if (clrString->Length < sizeof(cStr))
  sprintf(cStr, "%s", clrString);
std::string stlString(cStr);

No need to call the Marshal functions!

UPDATE Thanks to Eric, I've modified the sample code to check for the size of the input string to prevent buffer overflow.