Review of Pointers : Part Two

15.2 Review of Pointers : Part Two Review of pointers part two.

Lesson Transcript.

I am taking this review process slowly, to make sure that each concept is entirely mastered before we proceed. The next topic I want to review about pointers involves the differences between using the * character with a pointer.

The * character means exactly two things concerning a pointer. It means either "Make this variable a pointer", or it means: "What is at the address of the pointer". There is no other possibility.

When you first create a pointer, you use the * character and it means "I am making a pointer." That is all it means.

After a pointer is created, even if it has not yet been assigned, the * character takes on new meaning. It now means for the rest of your program: "what is at the address of".

    char *my_pointer = ...  // <--- Here and *only* here, the 
                            // * character means "I am creating 
                            // a pointer. 
    ...
    ... // <--- For the rest of the program, the 
    ... // * character when used with this pointer will 
    ... // mean "what is at the address contained in the pointer" 
 

So that covers the * character. At this stage it should be very clear to you that any time you ever see the * character used with a pointer, other than its creation, it means "what is at the address of" the memory address in the pointer.

Now, there is a term for this process. It is called dereferencing. This is the act of "seeing" what is at the memory address contained in a pointer. For example:

    char my_character = 'a';
    char *my_pointer = &my_character;
    printf("The character is %c ", *my_pointer);
 

In the third line, we are seeing the * character being used, and it is not part of the creation of the pointer, therefore the * character means we are asking for "what is at the memory address" of the pointer. Which is of course, the character 'a'.

Now, lastly lets review the & character in the context of pointers. It simply means "address of" and it will give you the memory address that anything resides at. You can use the & "address of" operator with variables, pointers, arrays, array elements, and more.

It might help to think of the & operator as a function that returns a memory address.

When you have finished this lesson, proceed to:

15.3 Review of Pointers : Part Three Review of pointers part three.

Computer Science for Everyone

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