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 type as the variable it's pointing at.
Declaring a pointer variable does not create the type of variable it points at. It creates a pointer variable.
Though pointers are declared with an asterisk they are 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 type as the pointer.
To assign a pointer to a variable, use an ampersand with the variable's name.
The address-of unary operator & is not the same as the bitwise & AND operator.

m_address = &memory;

s_address = string;

The pointer s_address would be used on the string array's elements.

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:

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 type of pointer as the variables it 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, though any math operation can be substituted.

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	Seen by The Compiler
`array+1`	An address	A pointer
`*(array+1)`	Contents of address, what lives there	A string
`((array+1))`	Contents of a character array	A character
`**(array+1)`	Same as above	Same as above