Chapter 11 Pointer Variables

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Chapter 11 Pointer Variables
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Declaring a Pointer Variable

• Declared with data type, and identifier
  type pointer_variable
• follows data type
• Usually no space between so more obvious
• Space allowed, so 1 or more would still work
• Reserves space for storage
• Must initialize or assign address

Lesson 11.1
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Assigning an Address

• Use the "address of" operator ()
• General form pointer_variable
  ordinary_variable

Lesson 11.1
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Using a Pointer Variable

• Can be used to access a value
• Unary operator used pointer_variable
• In executable statement, indicates value
• Common practice to use suffix ptr for pointer
  variables
• Example width_ptr

Lesson 11.1
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Pointer Operators

• Ampersand
• Address of
• Asterisk
• Get value at the address

Lesson 11.1
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Uses of

• Binary multiplication operator volume
  height depth width
• Declaration specifier indicating address to be
  stored in variable's memory cell double
  height_address
• Unary operator indicating to get value or access
  memory cells at addressed height_address
  10.5

Lesson 11.1
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Uses of

• Declaration of function header to indicate a
  reference void function1
  (double)
• In executable statement to indicate "address
  of" height_address height

Lesson 11.1
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Spacing a

• Somewhat flexible in declaration or header
  double height double
  height double height

• For multiple pointer declarations double
  height width

or
double height double width
Lesson 11.1
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Transferring Addresses to Functions

• In declaration and header use type in argument
  list type function (type, type) type
  funcName (type name, type name)
• In function call use variable in argument list
  to pass address identifier funcName (name1,
  name2)

Lesson 11.2
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Using Pointer for Array Transfer
rtype function (type, int) function (array,
num) rtype function (type b, int num_elem)
code using b with
brackets (bn)
Declaration
Call
Header
FunctionBody
Lesson 11.3
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Example
void function2 (double, int) int main ( )
double c5 2.1, 3.5, 6.4, 1.9, 4.5
function2 ( c, 5) void function2 (double b,
int num_elem)
Lesson 11.3
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Pointer Variables and Math

• Declare variable as pointer double b
• Holds address
• Can perform addition and subtraction
• Purpose of add is to advance to subsequent cell
  b 1 (double is 8 bytes, so adds 8 bytes)
• Subtraction goes back to previous memory cell
  b 1 (goes back 8 bytes)

Lesson 11.4
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Returning Array Address from Function
Example Function declaration and header
double get_array_address (double )
double get_array_address (double c ) Now a
return statement with variable thatindicates
address in the function body
return c
Lesson 11.5
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Pointer Variables

• Point to 2, 4, or 8 bytes of memory depending on
  type of variable
• Can point to entire array
• Holds address of beginning of array
• Pointer declaration indicates size of memory
  greater than single value

Lesson 11.6
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Creating Pointer to Arrays

• Example double (f) 2

• Example double (h) 3 5

Lesson 11.6
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typedef Statement

• Used to create an alias for a data type
• Note not a new data type
• Basic form typedef type synonym_1, synonym_n

Lesson 11.6
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Uses of typedef

• Improve readability and understandability of the
  code
• Easier to modify programs that are implementation
  dependent

Lesson 11.6
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Arrays and typedef

• General form typedef type name size
• type is the type of values in the array
• name is the alias to be used as the data type in
  a declaration
• size is array size

Lesson 11.6
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typedef for Pointer to Array

• General form typedef type (name) size
• type is type of values in array
• name is the alias to be used as data type in
  declaration
• size is array size

Lesson 11.6
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Returning a Pointer

• Given the example typedef double
  (array_ptr) 2
• Creates alias array_ptr for declarations of
  pointers to 1-D arrays of double with size 2
• array_ptr function2 (argument)
• Indicates pointer to 1-D array is returned from
  function

Lesson 11.6
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Multidimensional Arrays

• C sees array of arrays
• Example int a2 3 4
• Can work with whole (or 1) array
• Can use 2 arrays of 3 4
• Can use 6 arrays of 4
• Can use 24 integers
• Pointers int (b)3 4, (c)4, d, a
• Can assign addresses with operator ( b
  a0 )

Lesson 11.6
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Pointers to Objects

• Special arrow operator -gt
• Negative and greater than symbol with no space
  between
• Used to access members with object's address
• Declaring pointer Class_name ptr_name
• Initializing pointer ptr_name object_name
• Calling member function (2 argument example)
  ptr_name -gt function_name (arg1, arg2)

Lesson 11.7
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Pointers as Data Members

• General form class Class_name
  private type
  pointer_name public
  type function_name ( )

Lesson 11.8
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Dynamic Memory Allocation

• Optimize memory space with new and delete
  operators
• Reserve and unreserve memory while program is
  execution
• Pointer variables important because operators
  work with addresses of memory reserved

Lesson 11.9
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new Operator

• General form new type num_elements
• type is data type of array elements
• num_elements is number of array elements
• Reserves memory but does NOT fill with values
• new returns address of memory it reserves
• Value assigned to pointer variable of same type

type array_address
array_address new type num
Lesson 11.9
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delete Operator

• General form delete array_address
• array_address is pointer variable
• Releases memory stored at address indicated
• Knows size of memory reserved by new and releases
  memory for all the array
• delete address
• deletes memory for single element

Lesson 11.9
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Summary
Learned how to

• Declare and initialize pointer variables
• Pass addresses to functions
• Return an address from a function
• Reserve memory during execution
• Link classes with accessor functions