Convert a String^ to wstring C++

Question

I programmed a little Application in C++. There is a ListBox in the UI. And I want to use the selected Item of ListBox for an Algorithm where I can use only wstrings.

All in all I have two questions: -how can I convert my

    String^ curItem = listBox2->SelectedItem->ToString();

to a wstring test?

-What means the ^ in the code?

Thanks a lot!

Solution

It should be as simple as:

std::wstring result = msclr::interop::marshal_as<std::wstring>(curItem);

You'll also need header files to make that work:

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

---

What this marshal_as specialization looks like inside, for the curious:

#include <vcclr.h>
pin_ptr<WCHAR> content = PtrToStringChars(curItem);
std::wstring result(content, curItem->Length);

This works because System::String is stored as wide characters internally. If you wanted a std::string, you'd have to perform Unicode conversion with e.g. WideCharToMultiByte. Convenient that marshal_as handles all the details for you.

Comments

[Ben Voigt]

Yuck. I refuse to reinvent this particular wheel, especially since the reinvention uses wrongly-named functions. There's no HGLOBAL here at all. Using that code is a documentation nightmare, because you have to write comments explaining what the not-an-HGLOBAL pointers actually are.

[Maurice Reeves]

Actually, your answer is much better. I need to look into the marshal_as method. +1. Thanks for pointing the way.

[Ben Voigt]

I really want some help eradicating (well, downvoting) every answer that suggests StringToHGlobalAnsi for this. But that's a job for another day.

[Kipcak08]

Thanks Ben Voigt - I will test it - give me 5 mins :-)

[Maurice Reeves]

That'll be difficult, as this is the answer that even Microsoft recommends for this type of problem: msdn.microsoft.com/en-us/library/…

[Ben Voigt]

That's the StringToHGlobalAnsi page, they have to use that function. By no means does an example somewhere indicate that it's the best way to perform the task.

[Ben Voigt]

By the way, this doesn't get you a wide string.

[Maurice Reeves]

Right. But if you do a search, that's one of the more...referenced pages. For example: support.microsoft.com/kb/311259 Which I understand if your point. :-D

[Kipcak08]

ben can u tell me from where I get marshal_as? Also I have include the header file

[Ben Voigt]

@user1557170: oops, you need a second header file. Sorry about that.

[Kipcak08]

I'm now a little bit confused - can u simply tell me which code I need ? I'm not a pro programmer like u

[Ben Voigt]

Yes, which also mentions marshal_as. They could do a lot better job of emphasizing which one is better, though.

[Ben Voigt]

Just the first line, plus the two header files. Everything below the divider just explains what marshal_as actually does inside.

[Kipcak08]

should I need a speacial header file?

[Kipcak08]

My compiler tells me that marshal_as is not defined

[Maurice Reeves]

I agree. They make mention of when each method is mentioned, but do not indicate which is the best, preferred, etc.

[Ben Voigt]

@user1557170: There's a namespace too. Sorry for leaving that out. You can also say using namespace msclr::interop;

[Kipcak08]

yeah now it's working dude :-) Thanks for the great support you was a big help

[Kipcak08]

can u tell me what is the best way to get an pro programmer like you?

[Ben Voigt]

@user1557170: Practice. Follow tutorials written by experts. Solve small problems. Read other peoples' code that solves big problems. Learn from it. Write more code. Read more code. Ask what makes code good or bad and why.

[tfinniga]

I get error C2039: 'Data' : is not a member of 'System::String'

[Pol]

This work on WinRT with C++/CX not on the older CLR with C++/CLI.

[Juv]

I like this, because this is straight forward: String^ is in UTF16, and if std::wstring should also remain in UTF16 - there is no conversion needed just plain old copy of the characters. Voted Up.

[Robinson]

May I ask, does msclr::interop::marshal_as require any cleanup?

[Ben Voigt]

@Robinson: There are two groups of conversions, ones that require cleanup require you to create a marshal_context instance that performs the cleanup when it goes out of scope. Ones that don't require cleanup (because they return a smart object like std::string that knows how to clean itself up) use marshal_as. You can't get this wrong unless you do something crazy like intentionally leak a marshal_context object.