Bài giảng Introduction to computer programming

Ho Chi Minh City University of Technology

Faculty of Computer Science and Engineering

Chapter 8: Pointers

Introduction to Computer Programming

(C language)

TS. Võ Thị Ngọc Châu

([email protected]n,

[email protected])

2017 – 2018, Semester 2

Course Content

 C.1. Introduction to Computers and

Programming

 C.2. C Program Structure and its

Components

 C.3. Variables and Basic Data Types

 C.4. Selection Statements

 C.5. Repetition Statements

 C.6. Functions

 C.7. Arrays

 C.8. Pointers

 C.9. File Processing

2

References

 [1] “C: How to Program”, 7^thEd. – Paul

Deitel and Harvey Deitel, Prentice Hall, 2012.

 [2] “The C Programming Language”, 2^ndEd.

– Brian W. Kernighan and Dennis M. Ritchie,

Prentice Hall, 1988

 and others, especially those on the Internet

3

Content

 Introduction

 Declare and initialize pointers

 Operations on pointers

 Pointers and arrays

 Variable storage and heap memory

 Memory allocation and de-allocation

 Pointers and structures

 Pass pointers to a function

 Function pointers

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 Summary

Introduction - Recall - Chapter 2

 Main memory is addressable continuously.

 scanf() for input data from input devices to main memory

Input a string: Input

Input a character: A

Input an integer: -123

Input device = keyboard

Input

Input device = keyboard

A

Input device = keyboard

-123

Input

A

-123

Main memory ≈ variable

Varying size: user-predefined Fixed sizes: character = 1 byte, integer = 4 bytes, …

char aString[5];

…

scanf(“%s”, aString)

char aChar;

…

scanf(“%c”, &aChar)

int anInteger;

…

scanf(“%d”, &anInteger)

printf(“%s”, aString)

printf(“%c”, aChar)

printf(“%d”, anInteger)

Introduction - Recall - Chapter 3

 Built-in data types (primitive/fundamental)

 char (signed char), unsigned char

 short int, unsigned short, int, unsigned int, long int,

unsigned long int, long long int, unsigned long long

 float, double, long double

 void

 enum (enumerated data associated with integers)

 Derived data types

We haven‟t discussed

 arrays [] of objects of a given type

this derived data type

in detail yet!!!

 pointers * to objects of a given type

 structures struct containing objects of other types

 union containing any one of several objects of

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various types

Introduction - Recall - Chapter 3

Name

Operator

Description

Example

sizeof

sizeof(type),

sizeof(variable)

Returns the size (bytes) of sizeof(char)

a type or a variable

int anInt = 0;

sizeof(anInt);

address

&Variable

Returns the address of the char aChar;

memory named Variable

char* ptrChar;

ptrChar = &aChar;

Dereferencing

Index

*Pointer

Returns the value of the

aChar = *ptrChar + 1;

memory Pointer points to

Variable[..]

Returns the element at the int intArray[3];

index

intArray[0] = 0;

intArray[1] = 1;

intArray[2] = 2;

anInt = intArray[1];

Structure

member

Structure_

name.member

Refers to a member of a

particular structure

struct point pt;

pt.x = 10;

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Introduction - Recall - Chapter 6

A function to swap two integer numbers

void swap(int a, int b){

int temp;

a and b will be passed by

temp = a;

values of int type.

a = b;

b = temp;

}

void swap(int *a, int *b){

int temp;

a and b will be passed by pointers

to int values, i.e. addresses of the

memory that contains int values.

temp = *a;

*a = *b;

*b = temp;

}

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Introduction - Recall - Chapter 6

Stack‟s values when a=10 and

b=9 in the main() function

Callee‟s stack

Caller‟s stack

000000000022FE4C

&a

000000000022FE4C

000000000022FE48

10

9

a

b

a

000000000022FE48

&b

b

temp

Stack‟s values

before the callee

ends

Callee‟s stack

Caller‟s stack

000000000022FE4C

&a

&b

000000000022FE4C

000000000022FE48

9

a

b

a

000000000022FE48

10

b

10

temp

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Introduction - Recall - Chapter 7

int a[10] = {2, 3, -1, 0, 4, 7, 9};

a, array name, is the address of the first int memory location.

Access to a[5] returns an

int value: 4.

2

3

-1

0

4

7

9

0

index

0

1

2

3

4

5

6

7

8

9

int b[3][5] = {{2, 3, -1, 0, 4}, {7, 9}, {6, 11, -2, 5}};

b, array name, is the address of the first int memory location.

Access to b[2] returns

the address of b[2][0]

for the third row.

2

3

-1

0

4

7

9

0

6

11

-2

5

0

index

[0][0] [0][1] [0][2] [0][3] [0][4] [1][0] [1][1] [1][2] [1][3] [1][4] [2][0] [2][1] [2][2] [2][3] [2][4]

Access to b[0][2]

returns an int value: -1.

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Introduction - Recall - Chapter 7

 Pass a value of an element at index i of a one-dimension array a

to functions

Value passing - unchanged

 Call to function func: func(a[i], …)

 Pass all the values of the elements of a one-dimension array a

to functions

Address passing - changeable

 Call to function func: func(a, …)

 Pass a value of an element at indices i and j of a two-dimension

array b to functions

Value passing - unchanged

 Call to function func: func(b[i][j], …)

 Pass a row at index i of a two-dimension array b to functions

Address passing - changeable

 Call to function func: func(b[i], …)

 Pass all the values of the elements of a two-dimension array b

to functions

Address passing - changeable

 Call to function func: func(b, …)

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Introduction

 Related to physical memory addresses,

pointers are provided as

 A means for manipulation on memory

 A means for pass-by-reference implementation

 A means for dynamic data structures that can

grow and shrink at execution time

In Memory

[1], Figure 7.1, pp. 254

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In Memory

Declare and initialize pointers

 A pointer of a data type

 A variable whose value is an address of memory

location that contains a value of a data type

 Must be declared before its use

 optionally with an initial value

type_name* variable_name =_optexpression_opt;

- variable_name: a valid identifier for a pointer

- type_name: a valid data type (basic, derived, a new one with

typedef)

- type_name*: a pointer type for pointers that point to memory

location of a data type type_name

- expression: an initial value (0, NULL, an address)

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Declare and initialize pointers

type_name* variable_name =_optexpression_opt;

// a variable of the char data type

// an un-initialized pointer pointing to a char

// a null pointer pointing to a char

// a pointer pointing to a char with an

initialized pointer to aChar

pChar1

pChar2

pChar3

pChar4

???????

000000

22FE37

a

aChar

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Declare and initialize pointers

type_name* variable_name =_optexpression_opt;

// a variable of the int data type

// an un-initialized pointer pointing to an int

// a null pointer pointing to an int

// a pointer pointing to an int with an

initialized pointer to anInt

pInt1

pInt2

pInt3

pInt4

???????

000000

22FE38

10

anInt

15

Declare and initialize pointers

type_name* variable_name =_optexpression_opt;

// a variable of the float data type

// an un-initialized pointer pointing to a float

// a null pointer pointing to a float

// a pointer pointing to a float with an

initialized pointer to aFloat

pFloat1

pFloat2

pFloat3

pFloat4

???????

000000

22FE3C

10.5

aFloat

16

Declare and initialize pointers

type_name* variable_name =_optexpression_opt;

// a variable of the point3D data type

// an un-initialized pointer pointing to a point3D

// a null pointer pointing to a point3D

// a pointer pointing to a point3D with an

initialized pointer to aPoint

pPoint1

pPoint2

pPoint3

pPoint4

???????

000000

22FE40

1.0 2.0 3.0

aPoint

x

y

z

17

Declare and initialize pointers

22FE37

ptrChar

22FE37

a

aChar

22FE30

anInt

ptrInt

22FE30

9

ptrInteger

an int value in the memory

an address of the memory

location named anInt: 9

location named anInt: 22FE30

an address of the memory location

an int value in the memory

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pointed by ptrInt: 22FE30

location pointed by ptrInt: 9

Declare and initialize pointers

 A pointer of a data type

 A variable whose value is an address of memory

location that contains a value of a data type

 What if a particular data type is not told?

 Pointers to void

void * pointer;

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Declare and initialize pointers

 Pointers to void

 The generic pointer type which is a flexible means

to manipulate memory for any data type

 Adaptive data structures

 Function definitions

 A pointer to any data type can be assigned

directly to a pointer of type void *.

 A pointer of type void * can be assigned directly

to a pointer to any data type.

 A pointer of type void * can be casted to any data

type.

 A void * pointer cannot be dereferenced.

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Bài giảng Introduction to computer programming - Chapter 8: Pointers