IT计算机 primitive(原始的)

Chapter6

Cb/XCA,,S叶,Pro0grammingD

DataTypesLanguages

SIXTHEDITION

RobertW.Sebesta

PEARSON

Afklison

Copyrightc2004PiurwaAddHon-Wrdry.»MIright*mrnvd.ISBN0-321-19362-8

Chapter6Topics

•Introduction

•PrimitiveDataTypes

•CharacterStringTypes

•User-DefinedOrdinalTypes

•ArrayTypes

•AssociativeArrays

•RecordTypes

•UnionTypes

•PointerTypes

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Introduction

•ThisChapterintroducestheconceptof

adatatypeanddiscusses:

-Characteristicsofthecommonprimitive（原始的）

datatypes.

-Characterstrings

一Userdefineddata-types

-Designofenumerations（歹u聚）andsub-rangedata

types

-Designofstructureddatatypesincludingarrays,

records,unionsandsettypes.Heap堆稹

在相郝信者存军元中存放资料，

-Pointersandheapmanagement很像一槿堆叠操作。

但是，堆稹指上票保持指向

堆稹的第一彳固罩元，而不是

下一他可用的堆叠罩元。

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DataType

•Adatatypedefinesacollectionofdataobjects

andasetofpredefinedoperationsonthose

objects

•EveryPLneedsavarietyofdatatypesinorder

tobettermodel/matchtheworld

•Moredatatypesmakesprogrammingeasierbut

toomanydatatypesmightbeconfusing

•Whichdatatypesaremostcommon?Which

datatypesarenecessary?Whichdatatypesare

uncommonyetuseful?

•HowaredatatypesimplementedinthePL?

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EvolutionofDataTypes

•FORTRANI

-INTEGER,REAL,arrays

•COBOL

-Programmerscouldspecifyaccuracyofdecimal

-Introducedstructureddatatypesforrecords

•PL/I

-Extendedaccuracyspecificationtointegerandfloating­

point

•ALGOL68

-User-defineddatatypes

•Ada83

-Usercancreateuniquetypesforeveryclassofvariables

andthesystemenforces渤行）theuniquenessofthe

types.

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Descriptors

•Adescriptoristhecollectionofattributes

ofavariable

•Inanimplementation,adescriptoristhe

collectionofmemorycellsthatstore

variableattributes（燮数的腐性）

-Ifallattributesarestatic,thedescriptoris

requiredonlyatcompiletime

-Ifattributesaredynamic,partorallofthe

descriptormustbepresentduringexecution

-Inallcases,descriptorsareneededfor

•Typechecking

•Allocationanddeallocation信己意||的配置典解除）

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EvolutionofDataTypes

•DesignIssuesforalldatatypes:

-Whatisthesyntaxofreferencestovariables?

一Whatoperationsaredefinedandhowarethey

specified?

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Primitivedatatypes

•Aprimitivedatatypeisonethatisnotdefinedin

termsofothertypes

•Often,primitivetypesareareflectionofthe

underlyinghardware:

-Integer

-Floatingpoint

•Otherprimitivetypesrequirealittlenon-hardware

supportfortheirimplementation,Majorcategories

include

-Numeric（数彳直）

-Boolean（布林彳直）

-Character（字元）

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PrimitiveDataTypes

.：-Integer:ShortInt,Integer;LongInt(etc)

:-FloatingPoint:Real,DoublePrecision

Storedin3parts,signbit,exponentand

mantissa(seefig6.1)

-Decimal:BinaryCodedDecimal,BCD

(COBOL,C#,2digitsperbyte)

usedinbusinesslanguageswithasetdecimal

fordollarsandcents

-Boolean:(TRUE/FALSE,1/0,YES/NO)

'：-Character:UsingEBCDIC,ASCII,UNICODE,

etC.Mantissa尾数

由已知浮黑占数中的最高有效数位

系且成的定黑占数。浮黑占表示法中，

指一数值的小数部分。封数表示

法中，指非负值的小数部分。

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Numerictypes

•Integer:ShortInt,Integer,LongInt(etc)

-Almostalwaysanexactreflectionofhardware

•Twoscomplement件甫敷)tosavenegativeintegers,

whichisconvenientforadditionandsubtraction.

Intwos<omplementnotation,therepresentationofa

negativeintegerisformedbytakingthelogical

complementofthepositiveversionofthenumber

andaddingone.

•Chas8differentintegertypesbycombining

-char,short,int,long

一signedandunsigned

•AdaallowsSHORTINTEGER,INTEGER,LONG

-Somelanguagessupportintegersofunlimited

magnitude(implementedinsoftware)

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Numerictypes

Floating-point：Real,DoublePrecision

-Storedin3parts,signbit,exponentandmantissa（尾数）

-Modelrealnumbers,butareonlyapproximations

-Valuesaredefinedintermsofprecisionandrange

•Precisionistheaccuracyofthefractionalpart（小数部份）

•Rangeisacombinationoftherangeoffractionsand

exponents

•Adaexamples:

typeSPEEDisdigits7range0.0..1000.0;

typeVOLTAGEisdelta0.1range-0.0..5.0;

-Hardwaresupport:IEEEFloating-Point

Standard754:

•Singleprecision:32bits

-Signbit,8-bitexponent,23bitsignificand

•Doubleprecision:64bits

-Signbit,11-bitexponent,52bitsignificand

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IEEEFloatingPointStandard

•Singleprecision:32bitrepresentationwith1bit

sign,8bitexponent,23bitmantissa

•Doubleprecision:64bitrepresentationwith1bit

sign,11bitexponent,52bitmantissa

8bits23bits

ExponentFraction

tSignbit

Mantissa尾数

（a）由已知浮黑占数中的最高有效数位

系且成的定黑占数。浮黠表示法中，

指一数值的小数部分。卦数表示

,法中，指非负值的小数部分。

11bits52bits

ExponentFraction

tsignbit

(b)

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Numerictypes

•Decimal(十迤制)

-Usedmostlyforbusinessapplications

-Storesafixednumberofdecimaldigits,withthe

decimalpointatafixedposition

-Decimaldigitsarecoded(BinaryCodedDecimal,BCD

with2digitsperbyte,e.g.COBOL,C#)

-Arecapableofpreciselystoringdecimalvalueswithina

restrictedrange,especially,usedinbusinesslanguages

withasetdecimalfordollarsandcents

-Operationsaredoneinhardwareonmachinesthat

supportit;insoftwareonthosethatdonot

-ExamplefromPL/I:

DCLPAYRATEFIXEDDECIMAL(7,2);

-Advantage:accuracy

-Disadvantages:\\mtedrange,wastesmemory

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BooleanTypes

•Simplestofalltypes

•Rangeofvalueshasonly2elements,trueand

false

•IntroducedinALGOL60

•Couldberepresentedasasinglebit,butmost

oftenasabyte(thesmallestefficiently

addressablecellofmemory)

•CdoesdonotincludeaBooleantype;instead,

numericexpressionsareusedasconditionals

•Advantage:readability

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CharacterStrings

•Charactersareanotherprimitivedatatypewhichmapeasily

intointegers.Characterdataarestoredasnumericcodings

-ASCII

•8-bitallows256characters

•Inadequate（不遹）forglobalcommunication

-Unicode

•16-bitallows655536characters

•Includescharsctersfrommostoftheworld'snatural

languages

•Neededascomputersbecomelesseurocentric（西方的）to

representthefullrangeofnon-romanalphabetsand

pictographs（象形文字）.

•Javawasthefirstwidely-usedlanguagetousetheUnicode

characterset

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Characterstringtypes

•Valuesareasequenceofcharacters

•Designissues:

-Ischaracterstringaprimitivetypeorjustaspecial

kindofarray?

-Isthelengthofcharacterstringobjectsstaticor

dynamic?

•Operationsoncharacterstrings:

-Assignment

-Comparison(=,>,etc.)

-Concatenatione.g.(Ada)N:=N1&N2(字串结合)

-Substringreferencee.g.(Ada)N(2..4)

-Patternmatching

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CharacterstringsinAda

-STRINGisasomewhatprimitivetype

-STRINGisatypethatispredefinedasaone­

dimensionalarrayofCHARACTERelements:

S:STRING(l.-lO);

一Operationsinclude

•Substringreference:S(1..3)="Bob";

•Concatenation:S:="Bob"&"Alooga";

•Comparison:=,/=,<,<=,>,>=

-StringshavefixedlengthinAda

Concatenation512置

按规定的次序把雨他I字串结合篇一彳固

字串的一槿操作，所横成字串的畏度

等於甬彳固字串畏度之和。

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Characterstrings

inCandC++

一Notaprimitivetype

-chararraysstorecharacterstrings

I一Stringsareterminatedby、\0'->stringshave

limiteddynamiclength

-Thestandardlibrarystring.hincludesa

collectionofstringoperations,whichinclude

•strlen(stringlength)

■MffX•strcat(stringconcatenation)

•strcmp(stringcomparison)

•strcpy(stringcopy)

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CharacterstringsinJava

一Stringsareimplementedby2classes

•String—valuesareconstantstrings

•StringBuffer—valuesarechangeable

一Objectswhichareimmutable(tochangethe

length,youhavetocreateanewstringobject)

and+istheonlyoverloadedoperatorfor

string(concat),nooverloadingfor<,>,etc

一Operationsareprovidedviaclassmethods:

一Example:

Stringsi,s2,s3;

si="BobAlooga”;

s2=si+)Jr/7;

s3=sl.substring(0,3);

intp=sl.indexOfCAK');//p=4

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Characterstringsinothers

•Perl

-Patternsaredefinedintermsofregularexpressions

providingaverypowerfulfacility!

-Patternforidentifier:/[A-Za-z][A-Za-z\d]+/

-Patternfornumericliteral:/\d+\.?d*|\.\d+/

•SNOBOL4

-Theultimatestringmanipulationlanguage

-Stringisaprimitivetype

-Therearemanystringmanipulationoperations,

includingegborage信辛翥的）pattern-matching

•StringsinPerl,LISPandSNOBOL4have

dynamiclength.

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Characterstringsinothers

•FORTRAN77/90,COBOL,Ada-static

lengthstrings

e.g.InFORTRAN90

CHARACTER(LEN=15)NAME;

•PL/I,Pascal-variablelengthwithstatic

fixedsizestrings

•Somelanguages,e.g,Snobol,PerlandTel,

haveextensivebuilt-insupportforstrings

andoperationsonstrings.

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Evaluationofcharacterstring

•Characterstringsareimportanttothe

writabilityofalanguage.

•Dealingwithstringsasarraysmore

cumbersome（黄隹虑理的）thandealingwitha

primitivestringtype.

•Ifimplementedasaprimitivetypewith

staticlength,theyareinexpensive.Thus,

itisdifficulttojustifytheiromission.

•Dynamic-lengthstringsprovideadditional

flexibility,butaremoreexpensiveto

implement.

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Implementingcharacterstrings

•Staticlengthstrings

-Requireadescriptoronlyatcompiletime:

•Length(incharacters)

•Address(ofthefirstcharacter)

•Limiteddynamiclengthstrings

-Needaruntimedescriptorthatstores:

•Fixedmaximumlength

•Currentlength

•Addressoffirstcharacter

-CandC++stringsdonotrequirearun-timedescriptor

becausetheendofastringismarkedwiththenull

character

•Neitherstaticlengthnorlimiteddynamiclength

stringsrequireruntimestoragemanagement.

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descriptorcharacterstrings

Limiteddynamicstring

Maximumlength

Currentlength

Address

Compile-timeRun-timedescriptor

descriptorforstaticforlimiteddynamic

stringsstrings

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Implementingcharacterstrings

•Dynamic-lengthstringsrequiremorecomplex

storagemanagement.

•2approaches:linked时速系吉串列，^表（二讪海.）

_Linkedlist一系且资料元素目的集合‘其J嗔序排列方法是使

-每他项目包含下一偃P嗔目在重月窗存信者器中的位址。

•Advantage:

-Allowsnewlyrequiredcellstocomefrom

anywhereintheheap

•Drawbacks（不利脩件）：

-Storageoccupiedbylinks

-Someoperationsareslowedbythisrepresentation

-Storecompletestringsinadjacentcells（相鄢倨者存格）

•Advantage:

-Operationsarefaster

•Drawbacks:

-Whenstringgrowstheruntimesystemmustfinda

largeenoughblockofadjacentcells

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User-definedordinaltypes

•Anordinaltypeisoneinwhichtherangeof

possiblevaluescanbeeasilyassociatedwiththe

setofnonnegativeintegers

•Twocommonlyimplementedordinaltypes

一Enumeration（歹f］聚）type

•oneinwhichtheuserenumeratesallthepossible

values,whicharenamedsymbolicconstants

•CanbeusedinFor-loops,casestatements,etc.

•UsuallycannotbeI/Oeasily

•Mainlyusedforabstraction/readabiIity

ExampleinC#

enumdays{Mon,Tue,Wed,Thu,Fri,Sat,Sun};

0,1,2,3,4,5,6

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CandC++enumerationtypes

•Enumerationvaluesareimplicitlyconverted

tointeger.

•Namescannotbereusedwithsamescope

•Enumerationvaluesaresubjecttotherules

governingintegers.

•C++example:

enumcolortype{red,blue,green,yello,black);

colortypemyColor=blue,yourColor=red;

myColor++;wouldassigngreentomyColor.

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Pascalenumerationtypes

•Enumerationtypescanbeusedfor

-Arraysubscripts

-Forstatementvariables

-Casestatementselectors

•Cannotbeinputoroutput

•Namescannotbereusedinotherenumeration

types

•Pascalenumerationexample

typecolortype=(red,blue,green);

varcolor:colortype;

■■■

color:=blue;

ifcolor>red...

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Adaenumerationtypes

、•CanbeusedasinPascal

•Canbeinput/output(viaEnumeration_IO).

•Namescanbereused;disambiguationis

accomplishedbycontextorbyusing

type_namez

•Example:

鼠弋］typeDAYSis(MonzTue,WedzThuzFri,Sat,Sun);

0*typeWEEKDAYSis(MonJue,Wed,ThuzFri);

today,tomorrow:Day;

■■■

MflwforDayinWEEKDAYSloop...

JMSforDayinDAYSTue..DAYSTriloop...

today:=DAYSTREDftomorrow);

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Javaenumerationtypes

•Javadoesnotincludeanenumerationtype

•Enumerationtypesareclassesthatimplement

theEnumerationinterface

Classcolors{

Publicfinalintred=0;

Publicfinalintblue=1;

)

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User-definedordinaltypes

一Subrangetype:acontiguous（!®近的）

subsequenceofanordinaltypes

•Limitsalargetypetoacontiguoussubsequenceof

valueswithinthelargerrange

•providingadditionalflexibilityinprogrammingand

readability/abstraction

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Subrangetypes

•Pascal:

type

uppercase=

index=1..100;

•Ada:

subtypeWEEKDAYSisDAYSrangeMon..Fri;

subtypeINDEXisINTEGERrange1..100;

-Note:WEEKDAYSiscompatiblewithDAYS

INDEXiscompatiblewithINTEGER

-Ada'sderivedtypeisdifferentfromsubtype:

typeINDEX2isnewINTEGERrange1..100;

-notcompatiblewithINTEGERorINDEX

•Asisthecasewithenumerationtypes,

subrangetypesaidreadabilityandreliability.

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Implementingordinaltypes

•Enumerationtypesareimplementedas

integers,withthefirstvaluerepresented

as0,thenextvalueas1,etc,

•Thepermittedoperationsaredifferent

fromthoseofinteger.

•Subrangetypesareimplementedusing

theparenttypewithcodeinsertedbythe

compilertorestrictassignmentto

subrangevariables.

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Evaluationofenumerationtypes

Aidtoefficiency-e.g.,compilercanselectand

useacompactefficientrepresentation(e.g,,

smallintegers)

Aidtoreadability-Symbolicconstantsare

mucheasiertounderstandandrememberthan

integerliterals(e.g,,noneedtocodeacoloras

anumber)

Aidtomaintainability-e.g,zaddinganew

colordoesn'trequireupdatinghard-coded

constants.

Aidtoreliability-eg,compilercancheck

operationsandrangesofvalue.

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Arraytypes

•Anarrayisahomogeneousaggregate（聚集）of

dataelementsinwhichanelementisidentified

byitspositionintheaggregate,relativetothe

firstelement

•Referencestoelementsincludeoneormore

subscripts

•Referencesrequirearuntimecomputationto

determinethelocationbeingreferenced

•Arraytypesareimplementedinmost

programminglanguages

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Arraytypes

•Designissues

一Whattypesarelegalforsubscripts?

一Aresubscriptexpressionsrangechecked?

一Whenaresubscriptrangesbound?

一Whendoesallocationtakeplace?

一Whatisthemaximumnumberofsubscripts?

一Canarraysbeinitializedwhentheyhavetheir

storageallocated?

-Arearrayslicesallowed?

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ArraysandIndexes

•Indexingisamappingfromindicestoelementsin

anarray:

map(arrayName,indexValue)—>arrayelement

•Syntaxofindexingisfairlyuniversal:

arraynamefollowedbylistofindices,

eachsurroundedbyparenthesesorbrackets

-Ada,FORTRAN,PL/Iuseparentheses:()

-Otherlanguagesusebrackets:[]

•Subscripttypes

-FORTRAN,C,C++,andJavaallowintegersubscriptsonly

-Pascalallowsanyordinaltype

(int,boolean,char,enum)

-Adaallowsintegerorenumeration(歹U聚)types

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Fourcategoriesofarrays

•4categoriesofarraysbasedonsubscriptrange

bindingandstoragebinding:

-Static

-Fixedstackdynamic

-Stackdynamic

-Heapdynamic

•Insomelanguagesthelowerboundofthe

subscriptrangeisimplicit

-C,C++,Java—fixedat0

-FORTRAN—fixedat1

-Otherlanguagesrequireprogrammertospecifythe

subscriptrange.

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Staticarrays

•Staticarraysarethoseinwhich

一Rangeofsubscriptsisstaticallybound

一Storagebindingsarestatic

•Advantage:executionefficiencysinceno

dynamicallyallocation/deallocationis

required

•FORTRANarraysandsomearraysinAda

arestatic

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Fixedstack-dynamicarrays

•Fixedstack-dynamicarraysarethosein

which

-Subscriptrangesarestaticallybound

-Allocationisdoneatdeclarationelaborationtime

•Advantageisspaceefficiency

-Storageisallocatedonlywhileblockinwhicharrayis

declaredisactive.

-Storageforlargearraysin2differentprocedurescan

besharedaslongasbotharenotactive

simultaneously

•PascallocalarraysandClocalarraysthat

arenotstaticarefixedstack-dynamic

arrays

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Stack-dynamicarrays

•Astack-dynamicarrayisoneinwhich

-Subscriptrangesaredynamicallybound

-Storageallocationisdoneatruntime

-Bothremainfixedduringthelifetimeofthevariable

•Advantage:flexibility

•Adahasthiskindofarray:

declare

ARR:array(l..N)ofINTEGER;

begin

■■■

end;

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Heap-dynamicarrays

•Aheap-dynamicarrayisoneinwhich

-Subscriptrangebindingisdynamic

-Storageallocationisdynamic

-Eithercanchangeanynumberoftimesduringexecution

•Arrayscangrowandshrinkastheneedarises

•FORTRAN90hasdynamicarrays:

INTEGER,ALLOCATABLE,ARRAY%:)::MAT

ALLOCATE(MAT(10,20))

DEALLOCATE(MAT)

•CandC++allowdynamicarraysvia

-mallocandfree

-newanddelete

•APLandPerlarrayschangesizesasneeded

•Javaarraysareobjects(heapdynamic)

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Numberofsubscripts

Arraydimensions

•FORTRANI

一Allowedupto3subscripts

•FORTRAN77

一Allowsupto7subscripts

•C,C++,Java

-limitedto1butarrayscanbenested

(i,e.arrayelementisanarray)allowing

foranynumberofdimensions

•Otherslanguages

一Nolimitisspecified

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Arrayinitialization

FORTRAN:initializationatthetimestorageisallocated

INTEGERLIST⑶

DATALIST/10,20,30/

C,C++:lengthofarrayisimplicitbasedonlengthof

initializationlist

intlist[]={10,20,30);

charname[]=''bob";

char*names[]={''bob",〃sue”,〃tom〃};

Java

String[]names={''bob","sue","tom2;

AdadikeCbutyoucanspecifywhicharrayelementsare

assignedvalues(insteadofassigningallvalues)

LIST:array(1..5)ofINTEGER:=(1,2,3,4,5);

LIST2:array(l„10)ofINTGEGER:=

(1=>10,2..5=>100,others=>0);

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ArrayOperations

•APLhasmanyarrayoperations:

-+,・,*,/forvectors,matrices,andscalars

-Unaryoperatorsforreversingvectors,columnsorrows

ofmatrices

-Transposeorinvertamatrix

•Ada

-Array-arrayassignment

-Concatenationforany1-dimensionalarraytype

-Relationaloperators(=and/=)

•CandC++

-Notmuchinthewayofarrayoperations

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ArrayOperations

•Operationsthatapplytoanarrayasaunit(as

opposedtoasinglearrayelement)

•Mostlanguageshavedirectassignmentofone

arraytoanother(A:=B)ifbotharraysare

equivalent

•FORTRAN:AllowsarrayadditionA+B

•FORTRAN90:libraryofArrayopsincludingmatrix

multiplication,transpose

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ArrayOperationsinJava

•InJava,arraysareobjects(sometimescalled

aggregatetypes)

•Declarationofanarraymayomitsizeasin:

-int[]arrayl;

-arraylisapointerinitializedtonil

-atalaterpoint,thearraymaygetmemory

allocateditaswith

-arrayl=newint[100];

•Arrayoperationsotherthanaccess(arrayl[2])are

throughmethodssuchasarrayl.length

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Arrayslices

•Asliceissomesubstructureofanarray;

nothingmorethanareferencing

mechanism

•Examples:

-FORTRAN90

INTEGERMAT(1:4,1:4)

MAT(1:4,1)(1stcolumn)

MAT(2,1:4)(2ndrow)

一Ada

LIST(4..1O)

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ExampleslicesinFortran95

CUBE(2,1:3,1:4)CUBE(1:3,1:3,2:3)

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Arrayimplementation

•Compile-timedescriptorfora

1-dimensionalarraymayinclude:

一Elementtype

一Indextype

一Indexlowerbound

一Indexupperbound

一Address

•Formulti-dimensionalarrays,information

abouteachindexrangemustbestored.

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Arrayimplementation

•Anaccessfunctionisusedtomaparray

subscriptstoaddresses.

•Fora1-dimensionalarray,theaccess

functionforarrayarris

address(arr[k])=

addr(arr[lower_bound])+(k-

lower_bound)*element_size