Template Structures - PowerPoint Presentation

Slide1

Template Structures

Eric Roberts

CS 106B

February 11, 2013Slide2

Contest Results

The CS106B

Random Writer Contest

February 2013

Honorable Mention: Brad Girardeau (Word-Based Tom Sawyer)

Honorable Mention: Alexander Hsu (Hamlet with Semantics)

Honorable Mention: Alan

Kaptanoglu

(Paradise Lost)

Honorable Mention: Annette

Mullaney

(Sky High) Slide3

Shakespearean Sonnets

Awakes my heart; So true a fool is love,

thus shall excuse my jade,— A crow that flies

in heaven’s sweetest air. So shall I live,

as a dream. When wasteful war shall statues

overturn, And darkly bright, are themselves

as stone, Unmoved, cold, and times of

your memory. ’Gainst death, and lusty leaves quite gone, But when my glass shows me myself indeed

Beated and chopp’d with tanned antiquity, Mine eye my heart think that we before have heard them told. LXXVII Thy merit hath my pen,

—As ’twixt vows, and he in them I read; And

needy nothing

trimm’d

in jollity, And

sable curls, all bare, is of my speaking breast.

Runner-

Up #1

— Allan

RaventosSlide4

Winds of Democracy

And the winds of the north, from the great lakes,

and all the weapons of tyrants let loose,

but it will certainly come in use;

when the fire-flashing guns have fully alerted me,

and play with the measureless light.

Child: father what is that you express in your eyes?

It seems to me there are other men in other lands yearning and thoughtful, it seems to me if i could be content with all if i

thought them their own finale? This now is too lamentable a face for a man, and i looking up at the stars, and of each of us inevitable; each of us, for those being born.

Democracy!

Runner-

Up #2

— Tri DaoSlide5

Chicken-Heart Tom

breath would live near Tallapoosa’s

were thrust from it passed on Coosa’s

homesick that was no answer TOM dodged

for us all comb me

becuz

I never budgedfinished and then added: Poor Huck Finn’s

finally asked—dimly dreading Ben’swere thrown into secondary importancehumiliated and all this If you got your Nanceby a little by Tom lay waiting anxiety

like But at his name they turn his moietyon the cussed smothery houses Who artsaid go out of himself —chicken-heart

Runner-

Up #3

— Tommy TruongSlide6

Bob Dylan’s Random Writer Blues

F

Em/b

Well, he peak of the sun ’cause tonight

Dm F

an’ we gazed upon the road,

C Ammake promised that seaport town

C Fcalled on me to youF Em/bwith a pain that

i could not feel so sad.Dm Fdead man,C Amwhen

i’m

all alone one nights;

C F

forty-one days, all

i

gotta take a change possessed F Cby no special all rightG A

and cast off like crossin’ the bay of mexicoC Em/b

fanning to do whatever young,G Dforever you gotta do is survive,

 F Em/bWell, he’s a weird monkey, very funky.

Dm F

i

said for his age, he’s wild

C Am

my only prayer for him in the children

C F

who could give,

F

Em/b

we walked together,

Dm F

we’ll climb that hill no matter what gets in the dark does die

C Am

as the monks

C F

the

c.i.o

.

F C

by no special all right

G A

and cast off like crossin’ the bay of mexicoC Em/bfanning to do whatever young,G Dforever you gotta do is survive, F Em/bWell, tell me no lies.Dm Fare you one questions burning of the hangin’ on the bowery slumsC Amto those clothes and you’ll come baby, here’s too many booksC Fshe gone with a golden rule.F Em/byou always rightDm Fon a night longC Amlistenin’ for the wheel, took off her when he said, "that’s mine."C Fjoey, joey, F Cby no special all rightG Aand cast off like crossin’ the bay of mexicoC Em/bfanning to do whatever young,G Dforever you gotta do is survive 

First Place

— Jack MarisSlide7

Midterm Histogram

N

=

388

Median = 53.0/60Mean = 50.3/60

59–60

55–58

53–5451–5247–50

44–4641–4337–4034–36

25–33

00–24

A+

A

A–

B+

BB–C+

CC–DNP

64

109

35

33

44

27

19

16

10

23

8Slide8

Templates

One of the most powerful features in C++ is the template facility, which makes it possible to define functions and classes that work for a variety of types

.

template <typename

placeholder

>

where

placeholder

is an identifier that is used to stand for a specific type when the definition following the template specification is compiled.

The

most common form of a template specification isSlide9

Templates in Functions

Templates can be used before a function definition to create a generic collection of functions that can be applied to values of various types

.

The compiler will generate the code for many different versions of

max

, one for each type that the client uses.

The function max can be used only with types that implement the

> operator. If you call max on some type that doesn’t

, the compiler will signal an error.

template <

typename

ValueType

>

ValueType

max(ValueType v1, ValueType v2) {

return (v1 > v2) ? v1 : v2;}

The

following code, for example, creates a template for

the

max

function, which returns the larger of its two arguments: Slide10

Exercise: Rewrite

sort

as a Template

Rewrite the following code so that it sorts any type that implements the

< operator:

void

s

ort(int

array[], int n) {

for

(

int

lh = 0; lh

< n; lh+

+) { int

rh = lh;

for

(

int

i

=

lh

+

1;

i

<

n

;

i

+

+) {

if (array[i] < array[rh]) rh = i; } swap(array[lh], array[rh]); }}void swap(int & x, int & y) { int tmp = x; x = y; y

= tmp;}Slide11

Templates in Class Definitions

Templates are more commonly used to define generic classes. When they are used in this way, the

template

keyword must appear before the class definition and before each of the implementations of the member functions.

The most inconvenient aspect of using templates to create generic classes is that the compiler cannot process them correctly unless it has access to both the interface and the implementation at the same time. The effect of this restriction is that the .

h files for template classes must contain

both the prototypes and the corresponding code.To emphasize the conceptual separation between the interface and the associated implementation,

you should make sure to include an appropriate comment before the private section and the implementation warning casual clients away from the details.Slide12

A Template Version of the

Stack

ClassThe first step in writing the template version of the Stack class is to add the template keyword to the interface just before the class definition:

template <

typename

ValueType>

class

Stack

{

. . .

body of the class

. . .

};

Once you have made this change, each instance of the specific type (formerly

char in the

CharStack

class) must be replaced by the

ValueType

placeholder for the generic type, as in

ValueType

*elements;

or

void

push(ValueType

value);Slide13

Implementing the Template Class

The final change necessary to implement the template class is to add

template

declarations to

every method body, as in the following updated version of the constructor:

template <

typename

ValueType>

Stack<ValueType>::Stack(

) {

capacity = INITIAL_CAPACITY;

count = 0;

elements =

new ValueType[

capacity];}

Because of the restrictions that C++ imposes on template types, the implementations of the methods need to be included as part of the

stack.h header.Slide14

Assignment and Copy Constructors

There is one remaining issue about creating new abstract classes that is extremely important in practice, which is how such objects behave if you copy them using assignment or by passing them by value to parameters in methods.

The

crux of the problem is that copying an abstract data object typically needs to copy the underlying data and not just the fields directly accessible in the object. Unfortunately, the default interpretation in C++ is to copy only the top-level fields, which can lead to serious errors

.

Even though the text includes an extensive discussion of the issues surrounding assignment and copy constructors, we won’t hold you responsible for these topics in CS106B. If, however, you are applying for a job that requires you to use C++, you absolutely need to review this material.Slide15

Shallow

vs.

Deep Copying

Suppose that you have

a Stack<int> containing three elements as shown in the diagram to the right.A

shallow copy allocates new fields for the object itself and copies the information from the original. Unfortunately, the dynamic array is copied as an address, not the data.

A deep copy also copies the contents of the dynamic array and therefore creates two independent structures

elements

1000

capacity

100

count

3

10

20

30

1000

.

.

.

elements

1000

capacity

100

count

3

elements

2000

capacity

100

count

3

10

20

30

2000

.

.

.Slide16

Implementing Deep Copy Semantics

When you are defining a new abstract data type in C++, you typically need to define two methods to ensure that copies are handled correctly:

The operator

operator=

, which takes care of assignmentA copy constructor

, which takes care of by-value parameters

These methods have well-defined signatures and structures, and the easiest thing to do is simply to copy the code on the next slide, adapting it as necessary to account for the specific instance variables that need to be copied in the underlying representation.Slide17

/* Code to support deep copying for the

Stack class

*/

template <

typename

ValueType>

Stack<ValueType>::Stack(const

Stack & src) {

deepCopy(src);}

template <

typename

ValueType

>

Stack<ValueType> & Stack<

ValueType>::operator=(const Stack & src) { if (this != &

src) { if (elements != NULL) delete[] elements;

deepCopy(src); }

return *this;

}

template <

typename

ValueType

>

void Stack<

ValueType

>::

deepCopy(const

Stack &

src

) {

count = capacity =

src.count

;

elements = (capacity == 0) ? NULL : new

ValueType[capacity

];

for (

int

i = 0; i < count; i++) { elements[i] = src.elements[i]; }}Code to Implement Deep CopyingSlide18

The End