C++外文翻译Word文档格式.docx

C++外文翻译Word文档格式.docx

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,andMicrosoftWindows95operatingsystems,andApple®

Macintosh®

UNIX,andRISC（reducedinstructionsetcomputer）machines.Untilrecently,developerswantingtobuildversionsoftheirapplicationformorethanoneplatformhadfewchoices:

∙Maintainseparatecodebasesforeachplatform,writtentotheplatform'

snativeapplicationprogramminginterface（API）.

∙Writetoa"

virtualAPI"

suchasthoseprovidedbycross-platformtoolsets.

∙Buildtheirownmultiple-platformlayerandsupportit.

Today,however,anewchoiceexists.DeveloperscanusetheirexistingcodewrittentotheWindowsAPIand,usingtoolsavailablefromMicrosoftandthirdparties,recompileforalloftheplatformslistedabove.Thispaperlooksatthemethodsandsomeoftheissuesinvolvedindoingso.

Currentlythemostlucrativemarketforgraphicaluserinterface（GUI）applications,afterMicrosoftWindows,istheAppleMacintosh.However,vastdifferencesseparatethesewhollydifferentoperatingsystems,requiringdeveloperstolearnnewAPIs,programmingparadigms,andtools.Generally,MacintoshdevelopmentrequiresaseparatecodebasefromtheWindowssources,increasingthecomplexityofmaintenanceandenhancement.

BecauseportingcodefromWindowstotheMacintoshcanbethemostdifficultportingcase,thispaperconcentratesinthisarea.Ingeneral,ifyourcodebaseissufficientlyportabletoenablestraightforwardrecompilingfortheMacintosh（excludinganyplatform-specific,or"

edge"

code,youmayelecttoinclude）,you'

llfindthatitwillcomeuponotherplatformseasilyaswell.

MicrosoftVisualC++®

Cross-DevelopmentEditionforMacintosh（VisualC++forMac™）providesasetofWindowsNT–orWindows95–hostedtoolsforrecompilingyourWindowscodefortheMotorola680x0andPowerPCprocessors,andaportabilitylibrarythatimplementsWindowsontheMacintosh.ThisallowsyoutodevelopGUIapplicationswithasinglesourcecodebase（writtentotheWin32®

API）andimplementitonMicrosoftWindowsorAppleMacintoshplatforms.

Figure1,below,illustrateshowVisualC++forMacworks.Yoursourcecodeisedited,compiled,andlinkedonaWindowsNT–orWindows95–based（Intel）hostmachine.Thetoolscreate68000andPowerPCnativecodeandMacintoshresources.AnEthernet-basedorserialtransportlayer（TL）movestheresultingbinariestoaMacintoshtargetmachinerunningremotely.TheMacintoshapplicationisstartedontheMacintoshanddebuggedremotelyfromtheWindows-basedmachine.

NowthatApplehastwodifferentMacintosharchitecturestocontendwith（Motorola680x0andPowerPC）portabilityisparticularlyimportant.

Portingcaninvolveseveralsteps,dependingonwhetheryouareworkingwithold16-bitapplicationsorwithnew32-bitsources.Ingeneral,thestepstoaMacintoshportareasfollows:

1.Makeyourapplicationmoreportablebyfollowingsomegeneralportabilityguidelines.Thiswillhelpinsurenotonlyportabilitytothe680x0-basedMacintoshmachines,butalsotothenewer,morepowerfulPowerPCmachinesthatarebasedonaRISCchip.

2.PortyourapplicationfromWindows16-bitcodeto32-bitcode.Thismaybethemostcomplexandtime-consumingpartofthejob.

3.SegregatethosepartsofyourapplicationthatareuniquetoWindowsfromsimilarimplementationsthatarespecifictotheMacintosh.Thismayinvolveusingconditionalcompilationoritmayinvolvechangingthesourcetreeforyourproject.

4.PortyourWin32APIcodetotheMacintoshbyusingtheportabilitylibraryfortheMacintoshandVisualC++forcompiling,linking,anddebugging.

5.UsetheMicrosoftFoundationClassLibrary（MFC）version4.0toimplementnewfunctionalitysuchasOLE2.0containers,servers,andclientsordatabasesupportusingopendatabaseconnectivity（ODBC）.CodewrittenusingMFCishighlyportabletotheMacintosh.

6.WriteMacintosh-specificcodetotakeadvantageofuniqueMacintoshfeatures,suchasAppleEventsorPublishandSubscribe.

ThechiefchallengeamongthefamiliesofWindowsoperatingsystemsisthebreakfrom16bits（Windows3.11andWindowsforWorkgroups3.11operatingsystemwithintegratednetworking）to32bits（WindowsNTandWindows95）.Ingeneral,16-bitand32-bitcodebasesaresomewhatincompatible,unlesstheyarewrittenusingMFC.Developershavethechoiceofbranchingtheirsourcesintotwotrees,ormigratingeverythingto32bits.OncetheWin32choicehasbeenmade,howarelegacyplatformstoberun（thatis,machinesstillrunningWindows3.11）?

TheobviouschoiceistousetheWin32s®

APIlibraries,whichthunk32-bitcallsdowntotheir16-bitcounterparts.

DeveloperswhowanttheirapplicationstobeabletotakeadvantageofthehotnewRISChardware,suchasDECAlphaAXPmachines,canusethespecialmultipleplatformeditionsofVisualC++.TheseincludeversionsfortheMIPSR4000seriesofprocessorsaswellastheaforementionedDECAlphaAXPchipandtheMotorolaPowerPC.ThesetoolsetsrununderWindowsNT3.51andcreatehighlyoptimizednativeWin32applicationsforDECAlphaandMotorolaPowerPCplatforms.

DeveloperswhohaverecompiledtheirWin32sourcesusingthesetoolsetsareamazedathowsimpleitis.Sincetheoperatingsystemisidenticalonallplatforms,andthetoolsareidentical,littleworkhastobedoneinordertoachieveaport.ThekeydifferenceintheRISCmachinesfromIntelistheexistenceofanative64-bitinteger,whichisfarmoreefficientthanon32-bit（thatis,Intel）processors.

Microsoftworkscloselywithtwothird-partyUNIXtoolsproviders,BristolTechnologyandMainsoftCorporation,toallowdeveloperstorecompiletheirWin32-basedorMFC-basedapplicationsforUNIX.Developersseekingadditionalinformationshouldcontactthosecompaniesdirectly.

You'

llhavetodecideearlyonwhethertowritetothenativeAPI（Win32）ortoMFC.Ingeneralyou'

llfindMFCapplicationswillportmorequicklythanWin32applications.Thisisbecauseoneoftheintrinsicbenefitsofanapplicationframeworkisanabstractionofthecodeawayfromthenativeoperatingsystemtosomeextent.Thisabstractionislikeaninsurancepolicyforyou.However,developersfrequentlyhavequestionsaboutMFC,suchas:

∙WhatifIneedanoperatingsystemservicethatisn'

tpartoftheframework?

CalltheWin32APIdirectly.MFCneverpreventsyoufromcallinganyfunctionintheWin32APIdirectly.Justprecedeyourfunctioncallwiththeglobalscopeoperator（:

:

）.

∙Idon'

tknowC++.CanIstilluseMFC?

Sure.MFCisbasedonC++,butyoucanmixCandC++codeseamlessly.

∙HowcanIgetstartedusingMFC?

Startbytakingsomeclassesand/orreadingsomebooks.VisualC++shipswithafinetutorialonMFC（Scribble）.Then,checkouttheMFCMigrationKit（availableonCompuServeor,foramodestshippingandhandlingfee,fromMicrosoft）.ItwillhelpyoumigrateyourC-basedapplicationcodetoMFCandC++.

Allportingwillbeeasierifyoubegintodaywritingmoreportableprograms.Followingsomebasicportabilityguidelineswillmakeyourcodelessplatform-specific.

Neverassumeanything.Particularly,don'

tmakeassumptionsaboutthesizesoftypes,thestateofthemachineatanytime,byteordering,oralignment.

Don'

tassumethesizeofprimitivetypes,becausethesehavedifferentsizesondifferentprocessors.Forexample,anintistwobytesinWin16andfourbytesinWin32.Atallcosts,avoidcodethatreliesonthesizeofatype.Usesizeof（）instead.Todeterminetheoffsetofafieldinastructure,usetheoffsetof（）macro.Don'

ttrytocomputethismanually.

Useprogrammaticinterfacestoaccessallsystemorhidden"

objects,"

forexample,thestackorheap.

ParsingdatatypestoextractindividualbytesorevenbitscancauseproblemswhenportingfromWindowstotheMacintoshunlessyouarecarefultowritecodethatdoesn'

tassumeanyparticularbyteorder.LIMITS.Hcontainsconstantsthatcanbeusedtohelpwriteplatform-independentmacrostoaccessindividualbytesinaword.

Thismayseemobvious,becausenothingcouldbelessportablethanassemblylanguage.Compilers,suchasMicrosoftVisualC++,thatprovideinlineassemblersmakeiteasytoslipinalittleassemblercodetospeedthingsup.Ifyouwantportablecode,however,avoidthistemptation.Itmaynotbenecessary.Moderncompilerscanoftengeneratecodeasgoodashand-tunednativeassemblercode.OurownresearchatMicrosoftindicatesthatperformanceproblemsaremoreoftentheresultofpooralgorithmsthantheyareofpoorcodegeneration.Indeed,withRISCmachines,hand-turnednativeassemblercodemayactuallybeworsethanmachine-generatedcode,duetothecomplexityofinstructionschedulingandpickingregisterusage.

WriteallroutinesinCfirst;

then,ifyouabsolutelyneedtorewriteoneinassembler,besuretoleavebothimplementationsinyoursources,controlledbyconditionalcompiles,andkeepbothuptodate.

AmajorgoalofAmericanNationalStandardsInstitute（ANSI）C/C++istoprovideaportableimplementationofthelanguage.Theoretically,codewrittentostrictANSICcomplianceiscompletelyportabletoanycompilerthatimplementsthestandardcorrectly.MicrosoftVisualC++providesacompileroption（/Za）toenablestrictANSIcompatibilitychecking.

MicrosoftVisualC++providessomelanguagefeaturesthatareinadditiontoANSIC,suchasfour-characterconstantsandsingle-linecomments.ProgramsthatusetheMicrosoftCextensionsshouldbeportabletoallotherimplementationsofMicrosoftVisualC++.Thus,