Marshal::String ToXXX question

[Goran]

Hi all!

I need to pass managed String from to C-style APIs. I see I can use
Marshal::String ToXXX functions. Is this the best we have? I understand
this will allocate a new string and create copy of my String. I want to
pass it as constant (LPCWSTR). I don't need allocation and copying,
just the pointer. Can I have it, pretty please?

In normal C++, we usually have conversion operator or a function to get
it from a string class (string::c_str( ) or CString::operat or LPCTSTR or
_bstr_t::operat or LPCTSTR etc). Is there a similar thing in .NET?

Thanks, Goran.

[Jochen Kalmbach [MVP]]

Hi Goran!

I need to pass managed String from to C-style APIs. I see I can use
Marshal::String ToXXX functions. Is this the best we have? I understand
this will allocate a new string and create copy of my String. I want to
pass it as constant (LPCWSTR). I don't need allocation and copying,
just the pointer. Can I have it, pretty please?

If you just need an unciode-string, you can use (version for VC2003):

#include <vcclr.h>

const __wchar_t __pin * unmanaged_str = PtrToStringChar s(managed_str);

And use the "unmanaged_ str" pointer.
See also:
http://blog.kalmbachnet.de/?postid=18
http://support.microsoft.com/kb/311259/

In normal C++, we usually have conversion operator or a function to get
it from a string class (string::c_str( ) or CString::operat or LPCTSTR or
_bstr_t::operat or LPCTSTR etc). Is there a similar thing in .NET?

For conversion you could use the following (version for VC2005):

#include <windows.h>
#include <tchar.h>
#include <string>
using namespace System;
struct StringConvA
{
char *szAnsi;
StringConvA(Sys tem::String ^s)
:
szAnsi(static_c ast<char*>(Syst em::Runtime::In teropServices:: Marshal::String ToHGlobalAnsi(s ).ToPointer()))

{}
~StringConvA()
{

System::Runtime ::InteropServic es::Marshal::Fr eeHGlobal(IntPt r(szAnsi));
}
operator LPCSTR() const
{
return szAnsi;
}
};

struct StringConvW
{
wchar_t *szUnicode;
StringConvW(Sys tem::String^ s)
:
szUnicode(stati c_cast<wchar_t* >(System::Runti me::InteropServ ices::Marshal:: StringToHGlobal Uni(s).ToPointe r()))

{}
~StringConvW()
{

System::Runtime ::InteropServic es::Marshal::Fr eeHGlobal(IntPt r(szUnicode));
}
operator LPCWSTR() const
{
return szUnicode;
}
};

#ifdef _UNICODE
#define StringConvT StringConvW
#else
#define StringConvT StringConvA
#endif

int _tmain()
{
String ^s = "abc";
std::string ansi = StringConvA(s);
std::wstring unicode = StringConvW(s);
_tprintf(_T("%s "), (LPCTSTR) StringConvT(s)) ;
}

Greetings
Jochen