Pointers

• This is section 10.7, READ IT
• A pointer points at a place in memory.
• Book: A simple data type consisting of an unbounded set of values,m each of which addresses or otherwise indicates the location of a variable of a given type. Among the operations defined on pointer variables are assignment and testing of equality.
• A pointer really holds a memory address
  • This is at the implementation level.
  • We really should ignore this, but that is almost impossible.
• The & operator gives us a pointer to an variable, function, constant, ...
  • This is totally the wrong thing to do but:

  • int a;
    
    cout << "A pointer to a is " << & a <<  endl;
    	 

  • We declare pointers to specific data types

  • type * identifier

  • type * identifier, * identifier, * identifier

• Three special values
  • We need a default points to nowhere value.
  • Originally they used 0
  • Later they used NULL
  • Currently they wish us to use nullptr
• So we can declare pointers as follows

  • int * pointerToA  = 0;
    int * secondPtrToA = NULL;
    int * thirdPtrToA = nullptr;
    	

  • The choice is
    1. nullptr
    2. NULL
    3. 0 (but don't use this)
• Pointer Dereference
  • The dereference operator (*), also called the indirect operator
  • Indicates that the value pointed to by the pointer should be used, not the pointer
  • This is called indirect addressing
  • Code like a=7 is direct addressing.

  • cout << "*pointerToA = " << *pointerToA << endl;
    *pointerToA = 99
    cout << "*pointerToA = " << *pointerToA << endl;
    cout << "a = " << a << endl;
    	

• With structs and classes the dereference operator is ->

  • struct SimpleT{
        int one;
        string two;
    };
    ...
        SimpleT s1;
        SimpleT *s1Ptr = nullptr;
        s1Ptr = & s1;
        cout << "The name is " << s1Ptr->two << endl;
        s1Ptr->two = "This is changed ";