lesfarrell/pointer-cheatsheet

Pointer Cheatsheet

• 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.

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m_address = &memory;

To assign a pointer to an array, do not use the ampersand:

  s_address = string;

The pointer s_address would be used on the string array's elements. To assign a pointer to an array element, use the ampersand:

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.

Typical Pointer Setup and Use

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.

Pointers, Parenthesis and Math

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.

Pointers and array brackets

Array Notation	Pointer Equivalent
array[0]	*a
array[1]	*(a+1)
array[2]	*(a+2)
array[3]	*(a+3)
array[x]	*(a+x)

Ugly ** notation

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

Pointer Cheetsheet by Dan Gookin .