When not to use P/Invoke

Utilizing P/Invoke isn't fitting for all C-style methods in DLLs. Let's take an example where we create a string in a C++ program and display it in a C# application:

#include "stdafx.h"

const char * HelloMsg()
{
  char * msg = "Hello .NET Core.";
  return msg;
}
int main()
{
  printf(HelloMsg());
}

Now, using P/Invoke, pass the library in the DllImport attribute:

[DllImport("HelloMsgLib.so")]
public static extern char *  HelloMsg();

The trouble here is that we can't erase the memory for the unmanaged string returned by msg. Different methods called through P/Invoke restore a pointer and do not need to be deallocated by the client. For this situation, utilizing the marsheling is a more suitable approach.