How you can access data member inside the main program in c plus plus programming language?

Answer 1

Public, protected and private accessors only apply to code outside of the class. Instances of a class (objects) have complete and unrestricted access to all their own instance variables (data members). They also have unrestricted access to the instance members of all other instances of the same class whenever those instances are passed as arguments to a class member method. Static methods of the class have the same privilege, as do friends of the class.

So the question isn't why an object can access its own public members without using an operator or member function. Any code outside of the class has that exact same right, but if an object has unrestricted access to its protected and private members, why should its public members be treated any differently?

Answer 2

In Windows you can use the CreateFileMapping API to create shared memory in one program, and OpenFileMapping to access that memory from another program.

For a more generic approach, consider using disk files, pipes or messages.