How to free IntPtr in C#?

Question

How to free ptrSentFromPinvokedDLL?

IntPtr ptrSentFromPinvokedDLL= IntPtr.Zero;

int resultFromVendor = CallVendorDll(ref ptrSentFromPinvokedDLL);

resultFromVendor = DoMoreWorkFromVendorDLL(
    ptrSentFromPinvokedDLL, "workonthis");

// Free ptrSentFromPinvokedDLLhere

Answer 1

Ideally either the vendor worries about this or there would be a vendor function for deallocating the memory. If not, you need to know how the vendor allocated the memory. For example, if the vendor allocated the memory using LocalAlloc in kernel32.dll then you could free the memory using Marshal.FreeHGlobal(IntPtr). Similarly, if the COM memory allocator CoTaskMemAlloc was used then Marshal.FreeCoTaskMem(IntPtr) would be used to free the memory. So check the documentation and proceed accordingly.

For reference, here's a nice MSDN article about memory allocation models.

Answer 2

There is no way of knowing how to free it or if it even needs to be freed without seeing the code inside CallVendorDll. (Or some documentation)