How to marshal to ANSI string via attribute?

As stated in the linked article, when using [return: MarshalAs(UnmanagedType.LPStr)], the memory of the native string is freed by the CLR using FreeCoTaskMem(). If you manually create the managed string object via Marshal.PtrToStringAnsi(), the memory is not freed at all.

If it crashes, then probably the string was not created on the unmanaged side via CoTaskMemAlloc(), but via new() or malloc() (for example). The API of SDL_GetError() should state whose job it is to free the native string and how.

I did some digging. The source for SDL_GetError is:

const char *
SDL_GetError(void)
{
    static char errmsg[SDL_ERRBUFIZE];

    return SDL_GetErrorMsg(errmsg, SDL_ERRBUFIZE);
}

We can see that the memory for the string is allocated as a static char array. It is overwritten every time SDL_GetError is called. As such we can't and don't need to free it.

Since the [return: MarshalAs.*] methods all attempt to free memory after marshalling the type, they will not work (and further cause the program to crash).

As such, your (my) original solution is optimal.