What is the best way to convert between char* and System::String in C++/CLI

Question

What is the approved way to convert from char* to System::string and back in C++/CLI? I found a few references to marshal_to<> templated functions on Google, but it appears that this feature never made the cut for Visual Studio 2005 (and isn't in Visual Studio 2008 either, AFAIK). I have also seen some code on Stan Lippman's blog, but it's from 2004. I have also seen Marshal::StringToHGlobalAnsi(). Is there a method that is considered "best practice"?

Solution 1

There's a good overview here (this marshaling support added for VS2008): http://www.codeproject.com/KB/mcpp/OrcasMarshalAs.aspx

Solution 2

System::String has a constructor that takes a char*:

 using namespace system;
 const char* charstr = "Hello, world!";
 String^ clistr = gcnew String(charstr);
 Console::WriteLine(clistr);

Getting a char* back is a bit harder, but not too bad:

 IntPtr p = Marshal::StringToHGlobalAnsi(clistr);
 char *pNewCharStr = static_cast<char*>(p.ToPointer());
 cout << pNewCharStr << endl;
 Marshal::FreeHGlobal(p);

Comments

[Anthony Serdyukov]

+1, System::String constructor also takes length and encoding!

[Ben Voigt]

Marshal::StringToHGlobalAnsi is a poor option compared to marshal_context (as mentioned by Matthew), which uses RAII to automatically free the buffer. Not to mention that the name is totally wrong, it doesn't return an HGLOBAL at all.

[Patrick.SE]

Probably have to Marshal::FreeHGlobal(IntPtr((void*)chars)); it

[dko]

@Pat yes sorry I should have updated this after this. I did get it working well now. Moving it to .NET increased the performance of this app by 3x. Even marshaling things around.

[gatopeich]

Thanks, but that is a lengthy explanation. This goes more to the point: #include <msclr\marshal.h> // marshal_context context; // my_c_string = context.marshal_as<const char*>(my_csharp_string);

[Mugen]

For those who wonder, the full namespace for context is msclr::interop::marshal_context

[Dewey Vozel]

Your example does not work for me in C++/CLI using .NET 4.6.1. There is no System::String constructor that takes a char*... only signed char* or wchar_t*

[Ben Straub]

It's been a while since I've been in this world, but I believe this should still work. According to the docs at docs.microsoft.com/en-us/cpp/windows/…, you should still be able to gcnew a string with a char * string as the argument. Maybe you can cast to signed char *?

[Menace]

From my experience the pointer also has no nul terminator. You need to use clistr.Length to know how long it is.