Pointer Cheat Sheet

This page is based on information that appeared on the tear-out Cheat Sheet from C For Dummies, Volume II.

Pointer Pointers

A pointer must always be of the same data type as the variable it's referencing.
Though pointers are declared with an asterisk they're not always used with an asterisk.
The asterisk is the unary * operator. It is not the * multiplication operator.
Pointers must be initialized before they can be used!
Initialize a pointer by assigning it to a variable; the variable must be of the same data type as the pointer.
To assign a pointer to a variable, use an ampersand (&) operator on variable's.
The address-of unary operator & is not the same as the bitwise & AND operator.

m_address = &memory;

s_address = string;

element = &string[2];

Without an asterisk, an initialized pointer holds a memory address.
With an asterisk, an initialized pointer references the value stored at its address.

First, create a pointer of the proper type:

float *f;

Second assign it to a variable's memory location, assuming both variables are of the same data type:

f = &boat;

Finally, use the pointer:

printf("%.0f",*f);

Without an asterisk, the pointer references a memory location.
With an asterisk, the pointer references the value at that memory location.
Always use the same data type as the variables the pointer examines: floats for floats, ints for ints, and so on.
Remember: initialize a pointer before you use it! Set the pointer equal to the address of some variable in memory.

Pointer Thing	Memory Address	Memory Contents
`p`	Yep	Nope
`*p`	Nope	Yep
`*p++`	Incremented after value is read	Unchanged
`*(p++)`	Incremented after value is read	Unchanged
`(*p)++`	Unchanged	Incremented after it's used
`*++p`	Incremented before value is read	Unchanged
`*(++p)`	Incremented before value is read	Unchanged
`++*p`	Unchanged	Incremented before it's used
`++(*p)`	Unchanged	Incremented before it's used
`p*++`	Not a pointer	Not a pointer
`p++*`	Not a pointer	Not a pointer

The ++ operator is used above for illustration purposes.

A tip: Use parenthesis to isolate part of the pointer problem and the answer will always work out the way you intended.

Doodad	What It Is	Data Type
`*array[]`	An array of pointers	Array
`**array`	An array of pointers	Array (double pointer)
`array+1`	An address	Pointer
`*(array+1)`	Contents of address, what lives there	String/pointer
`(array+n)`	Character n in the string at `*array` (where 0 is the first character)	Character