How Can I Use C Class Member Functions in pthreads?

Incorporating Class Member Functions into Threads

In C , class member functions inherently carry a hidden parameter known as "this." This poses a challenge when attempting to create threads using member functions, as the standard library's pthread_create() function expects a function pointer without such parameters.

Compilation Error: Unable to Convert Function Pointer

As the initial code snippet illustrates, trying to pass a class member function to pthread_create() directly leads to a compilation error:

pthread_create(&t1, NULL, &c[0].print, NULL);

The compiler complains that it cannot convert the member function pointer (void* (tree_item::*)(void*)) to the expected function pointer type (void* (*)(void*)).

Solution: Static Class Method or Independent Function

To circumvent this issue, there are two viable approaches:

1. Static Class Method:
   Define a static class method (which does not accept a "this" pointer) that encapsulates the desired functionality:

   class C
   {
   public:
       void *hello(void)
       {
           std::cout << "Hello, world!" << std::endl;
           return 0;
       }
   
       static void *hello_helper(void *context)
       {
           return ((C *)context)->hello();
       }
   };

2. Independent Function:
   Create a separate function that serves as a wrapper around the class member function, explicitly passing in the "this" pointer as an argument:

   void hello_wrapper(void *context)
   {
       C *object = (C *)context;
       object->print();
   }

Thread Creation Using Static Class Method or Wrapper Function

With either of these approaches, you can now use pthread_create() to create threads that will execute the desired class member functions:

C c;
pthread_create(&t, NULL, &C::hello_helper, &c);  // Static Class Method

pthread_create(&t, NULL, &hello_wrapper, &c);  // Wrapper Function

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