NULL pointer and void pointer?

[NMTop40]

void * is also commonly used in standard APIs. For example, a thread function takes a void * parameter, a generic way of being able to pass it data.

This is how C APIs are often done, but in C++ APIs it is better to define a base class and expect a pointer to the base class.

Threads, for example, can be done like this:

// in header:

class ThreadClass
{
public:
   virtual ThreadClass* threadFunc() = 0;
};

thread_t create_thread( ThreadClass * pThreadClass );

/// in .cxx file

namespace
{
  extern "C" void * the_one_thread_function( void * param )
  {
      ThreadClass * pThreadClass( reinterpret_cast< ThreadClass * >(param ) );
      return pThreadClass->threadFunc();
  }
}

thread_t create_thread( ThreadClass * pThreadClass )
{
   thread_t result;
   pthread_create( &result, 0, the_one_thread_function, 0 );
   return result;
}

This is a very loose description to show how one might start writing a C++ wrapper to pthread_create which removes the need for void *. (The return value of the thread function is also void *, and you might want to use a different class, a ThreadResult class).

(If you want to implement this in full, then it is probably a good idea to take an optional thread-attribute parameter (2nd parameter to pthread_create). You'd also need some kind of collection (somewhere to store the ThreadFunc object and subsequently be able to delete it), thus a thread pool ).