To convert a 'std::string' to a C# 'System::String' in C++, you can use 'msclr::interop::marshal_as' This header gives you utilities to use for converting between managed and native types, more on this here -
Managed C++ to C# Conversion[
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#include <msclr/marshal_cppstd.h>
std::string s = "YourStandardStringHere";
System::String^ csString = msclr::interop::marshal_as<System::String^>(s);