make IntPtr in C#.NET point to string value

Question

I am using a class which has StringHandle field which is an IntPtr value that represents a LPCWSTR in C++.

internal IntPtr StringHandle; // LPCWSTR

say now that I have a String: string x = "abcdefg"

How can I use the String handle to point to the beginning of the String so that it is like C++ LPCWSTR ?

Answer 1

You need to copy the string to the unmanaged memory first and then get the IntPtr from that location. You can do so like:

IntPtr strPtr = Marshal.StringToHGlobalUni(x);

also, you need to make sure to free the unmanaged memory:

Marshal.FreeHGlobal(strPtr);

it's best to do all this in a try/finally.

Answer 2

Managed strings move in memory when the garbage collector compacts the heap. So they don't have a stable address and can't directly be cast to a LPCWSTR. You'll need to either pin the string with GCHandle.Alloc() to use GCHandle.AddrOfPinnedObject or copy it into unmanaged memory with Marshal.StringToHGlobalUni().

Strongly prefer copying if the address needs to be stable for a while.