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Question

If i have a c++ function which returns a char* like this:

char *cctalk_app_event_name(DG_CCTALK_APP_EVT_CODE);

And the corresponding C# signature:

[System.Runtime.InteropServices.DllImportAttribute("cctalk.dll", EntryPoint = "cctalk_app_event_name", CallingConvention = CallingConvention.Cdecl)]
    public static extern System.IntPtr cctalk_app_event_name(DG_CCTALK_APP_EVT_CODE param0);

If the native code returns a char* allocated with the new keyword, i am for sure gonna have a memleak each time i call this function C#? Is there a way i can free that memory?

Answer 1

My hunch from looking at the function name is that this may well be returning a pointer to a string constant within the DLL, in which case you don't need to worry about freeing the pointer anyway.

If the manual for the SDK ( link here ) wasn't any use, then I'd disassemble the DLL and look at what that function did, but don't worry about how to delete it before you've established that you need to.

Answer 2

If you don't have any documentation or source then you cannot know whether or not the memory was allocated with new. If it was allocated with new then it needs to be deallocated with delete. That can only be done from the native code. If that is needed then the DLL will need to export a deallocator for you.

Other possibilities include allocation from a shared heap, eg the COM heap. Not very likely. Or perhaps the string is statically allocated and does not need deallocation. This final option is usually the case when a functions returns a C string as a return value. If you had to guess, that's the percentage option. In any case, if there's no way for you to deallocate the string, what else can you do?

The only way you can be sure is to have documentation, or source code, or support from the author. I appreciate that you want to know the solution, but your only hope are the options listed in the first sentence of this paragraph.

I find it hard to believe that a library this complex has no documentation. How did you come by this library? Are you really sure there are no docs?