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Win32 Security in Managed C++


Strings in Managed C++

Strings in Managed C++

Converting from a C-string to a managed string is nice and straightforward, as System::String contains appropriate constructors. However, going the other way is a bit of a pain (and it is not particularly well publicized in the documentation). You need to call the StringToHGlobalUni() or StringToHGlobalAnsi() methods of System::Runtime::InteropServices::Marshal type to allocate it, followed by ToPointer() on the IntPtr instance returned by them. When you're done with the string, don't forget to release it by calling Marshal's FreeHGlobal() method:

wchar_t *pwszUserName = (wchar_t*)(Marshal::StringToHGlobalUni(userName).ToPointer());

size_t si;

PSID psid = Sec_AllocSidFromUserNameW(pwszUserName, &si);

Marshal::FreeHGlobal(pwszUserName);

Another thing worth mentioning is that just because you're in Managed C++, there's no reason why you must eschew all of your useful C/C++ libraries. Specifically, it's surprising how C++ aficionados forget the incredible utility of sprintf() and start flailing around with ToString() and Concat(). Consider the following possible implementations of LUID::ToString() (an LUID — Locally Unique ID — is used to uniquely identify a privilege, like an ATOM does for strings):

String *LUID::ToString()

{

return String::Concat(HighPart.ToString(), "-", LowPart.ToString());

}

String *LUID::ToString()

{

wchar_t sz[31];

wsprintfW(sz, L"%d-%u", HighPart, LowPart);

return new String(sz);

}

The first one might have fewer lines, but which one do you think will be faster (and have fewer allocations)?

— M.W.


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