Pointers

Concepts

A pointer is a reference to a "container" that can hold a value.

The "container" has a location and a type.

Pointers might or might not be directly supported by a programming language, but the logical concept is still useful in languages such as Fortran and Basic.

"Real Pointers"

We are talking about "machine level pointers" here.

A location is a memory address -- i.e., a number that identifies which byte in the computer's memory we are talking about.

The type determines how many bytes after the address are involved.

Notation

Boxes and arrows are the universal graphical notation.

It's just a convenience and helps get the right side of your brain engaged.

Why are pointers of interest?

• They allow you to refer to large data structures in a compact way

• They facilitate sharing between different parts of programs

• They make it possible to get new memory dynamically as your program is running

• They make it easy to represent relationships among data items.

Why are pointers dangerous?

They are a powerful low-level device. Undisciplined use can be confusing and thus the source of subtle, hard to find bugs.

Many advanced higher-level languages (e.g., Java, Lisp) do not need or use pointers.