symbian c++ coding idioms

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1、CodingidiomsforSymbianOSVersion1.01,Oct20021.IntroductionThisdocumentisaimedatallSymbianOSsmartphonedevelopers.Theapocryphal80-20rulestatesthat80%ofthetimewillbespentfixing20%oftheproblemsthatoccurindevelopment.Theaimofthisdocumentistoaddressthose20%.2.MemoryThissectioncontains

2、areviewofthetechniquesthatSymbianOSprovidesforpreventingmemory-relatedproblems.Alldevelopersshouldunderstandthiswell–itistheHolyGrailofSymbianOSprogramming!2.1Reviewofthecleanupstack2.1.1Allprogramsshouldcheckforout-of-resourceerrorsInanyapplication,anerrormayoccuratruntimeduet

3、oalackofresources:forexample,themachinerunningoutofmemoryoracommunicationportbeingunavailable.Thistypeoferrorisknownasanexception.Anexceptionshouldbedistinguishedfromaprogrammingerror:aprogrammingerrorcanbeaddressedbyfixingtheprogram,butitisimpossibletomakeaprogramfreefromthepo

4、ssibilityofanexceptionoccurring.Therefore,programsshouldbeabletorecoverfromexceptionswhentheyoccur.ThisisparticularlyimportantinSymbianOS,forthefollowingreasons:•SymbianOSapplicationsaredesignedtorunforlongperiods(monthsorevenyears)withoutinterruptionorsystemre-boot.•SymbianOSa

5、pplicationsaredesignedtorunonmachinesthathavelimitedresources,particularlymemory.Therefore,anout-of-resourceerrorismorelikelytooccurthaninadesktopapplication2.1.2Conventionalerror-checkingmethodsInaconventionalCorC++program,anifstatementmighttypicallybeusedtocheckforanout-of-re

6、sourceerror.Forexample:if((myObject=newCSomeObject())==NULL)PerformSomeErrorCode();2.1.3ProblemswithconventionalmethodsThereareproblemswiththisconventionalapproach:•Itrequiresmanyextralinesofcodetoputsucherrorcheckingroundeverysinglefunctionthatmightcauseanout-of-resourceerror.

7、Thisincreasescodesizeandreducesreadability.•Ifaconstructorfailstoallocateresources,thereisnowaytoreturnanerrorcode,becauseconstructorshavenoreturnvalue.Theresultwouldbeanincompletelyallocatedobject,whichcouldcauseaprogramcrash.C++exceptionhandling(try,catchandthrow)providessolu

8、tionstotheseproblems,butitisnotusedinSymbianOS,because