Teach Yourself Borland C++ in 14 Days - portal

68 Day 3
Pointers: Welcome to My Nightmare
Pointers are one of the most confusing aspects of the C++ language. They are also one of the
most powerful features of C++. My goal in this section is not to teach you the textbook
definition of pointers, but rather to teach you pointers in the context of how you will use them
in your C++Builder programs. So what is a pointer? It’s a variable that holds the address of
another variable. There, that wasn’t so bad, was it? I wish it were that simple! Because a pointer
holds the address of another variable, it is said to “point to” the second variable. This is called
indirection because the pointer does not have a direct association with the actual data, but
rather an indirect association.
A pointer is a variable that holds the address of another variable.
NEW TERM
NEW TERM
NOTE
Because the pointer does not have a direct association with the actual data,
indirection is the term used when referring to this indirect association.
Let’s look at an example. Earlier we talked about arrays. Let’s say that you had an array of ints.
You could access the individual elements of the array using the subscript operator, as I talked
about on Day 1, “Getting Your Feet Wet”:
int array[] = { 5, 10, 15, 20, 25 };
int someVariable = array[3]; // the value 20
You could also use a pointer to accomplish the same thing:
int array[] = { 5, 10, 15, 20, 25 };
int* ptr = array;
int someVariable = ptr[3];
In this example, the memory location of the beginning of the array is assigned to the pointer
named ptr. Note that the pointer is a pointer of the data type int and that the indirection
operator (the * symbol) is used when you declare a pointer. You can declare a pointer to any
of the integral data types (int, char, long, short, and so on), as well as a pointer to objects
(structures or classes). After the assignment the pointer contains the memory address of the
start of the array, and as such points to the array.
The name of an array variable, when used without the subscript
operator, returns the memory address of the first element of the array.
Put another way, the variable name of an array is a pointer, to the start
of the array. That makes it possible to assign an array to a pointer, as in
the preceding example.