Dereferencing Pointers

Section 18.4 Dereferencing Pointers

So how do we use a pointer? We know that the pointer stores a memory address. But how do we use that address to access the data at that address?

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The answer is to dereference the pointer. Dereferencing a pointer means using the memory address to access the data at the address it points to. The dereference operator is the asterisk (*). For example, if p is a pointer to an int, then *p is the int that p points to. If p holds the address of an int variable, then *p gives us access to the memory at that address. A good way to pronounce *p is “the thing p points at”.

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Note 18.4.1.

This is another time where C++ reuses the same symbol to mean different things. * can be used to specify that a data type is a pointer. It can also be used to dereference a pointer. Or it can mean multiplication.

When a data type is to its left, as in int* or double*, it modifies that type to say “pointer to a ....”. (There may or may not be a variable name to the right.)
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When there is no data type to its left and there is a value that is a pointer to its right, as in *p, it says to dereference p.
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When used between two numeric values, like x * y, it means multiply.
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To see dereferencing in action, try this sample in both ActiveCode and with CodeLens:

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Listing 18.4.1.

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In that example, we use *p to read the “int that p points to”. We can also use it to modify that value. If I have a pointer p and I want to modify the value that it is pointing at, I can do something like *p = 20;. We could pronounce *p = 12; as “the thing that p points at gets assigned 20”. Here is a sample of using a pointer to modify a value it points at:

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Listing 18.4.2.

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