c++ - Can members of a derived class can be accessed when its casted to base class? -

this question has answer here:

• polymorphism in c++ 9 answers

i put simple example illustrate question. here base class.

#include <mutex> #include <atomic>  class task { public:     task()     {         empty.store(true);     }     std::mutex access;     std::atomic<bool> empty;     virtual void work() = 0; }; 

this derived class.

#include <stdlib.h>  class exampletask : public task { public:     void work()     {         for(int = 0; < 16; ++i)         {             data[i] = rand();         }     } private:     int data[16]; }; 

as can see, example tasks or jobs done asynchronously. imagine, there queue of tasks , bunch of worker threads, maybe 1 each cpu core on target machine.

the task queue stores tasks casted base class, worker threads can pick next job queue , call work().

std::list<task*> queue;  exampletask *example = new exampletask(); queue.push_back((task*)example); 

a worker thread fetch first task, remove queue, , work on it.

while(true) {     task *current = queue.front();     queue.erase(queue.begin());     current->work(); } 

would concept work? can data accessed when current->work() called, if deal pointer base class?

yes: reference/pointer base class can implicitly converted pointer/reference derived class. how crtp , static polymorphism works:

template<typename t> struct crtp_base {     void execute()     {         static_cast<t*>(this)->f(); //the instance casted known derived class, , use derived class function f.     } };  struct foo : public crtp_base<foo> {     void f()     {         std::cout << "wow, compile-time resolved polymorphism!" << std::endl;     } };  int main() {    foo my_foo_instance;    crtp_base<foo>& base_reference = my_foo_instance;    base_reference.execute(); }; 

this prints:

wow, compile-time resolved polymorphism!

here running example.