DynamicMemoryAllocationppt动态内存allocationppt

《DynamicMemoryAllocationppt动态内存allocationppt》由会员上传分享，免费在线阅读，更多相关内容在教育资源-天天文库。

1、DynamicMemoryAllocationAllofthecodewehavewrittenuptonowallocatesspacefordataatcompiletime.Wespecifythevariablesandthearraysizesthatweneedinthesourcecode,andthat’swhatwillbeallocatedwhentheprogramexecutes,whetherweneeditornot.Workingwithafixedsetofvariablesinaprogramcanbeveryrestrictive,anditi

2、softenwasteful.DynamicMemoryAllocation1tMynThesolutionistousedynamicmemoryallocation,whichmeansthatyouallocatethememoryyouneedtostorethedatayouareworkingwithwhenyourprogramexecutes(runtime),ratherthanwhenyoucompileit(compiletime).Dynamicallyallocatedvariablescan’tbedeclaredatcompiletime,andso

3、theycan’tbenamedinyoursourceprogram.Whenyouallocatememorydynamically,thespacethatismadeavailablebyyourrequestisidentifiedbyitsaddress.Theobviousplacetostorethisaddressisinapointer.DynamicMemoryAllocation2tMynMemoryAllocatedStaticallyMemoryAllocatedDynamicallyFixedDataAreaInflexibleWastefulFix

4、edcapacityProgramCodeProgramCodeFixedDataAreaDataareaallocateddynamicallyatruntimeFlexibleEfficientVariablecapacityDynamicMemoryAllocation3tMynInmostinstances,thereisunusedmemoryinyourcomputerwhenyourprogramisexecuted.InC++,thisunusedmemoryiscalledthefreestore,orsometimestheheap.Youcanallocat

5、espacewithinthefreestoreforanewvariableofagiventypebyusingaspecialC++operatorthatreturnstheaddressofthespaceallocated.Thisoperatorisnew,anditiscomplementedbytheoperatordelete,whichde-allocatesmemorythatyouhavepreviouslyallocatedwithnew.DynamicMemoryAllocation4tMynYoucanallocatespaceinthefrees

6、toreforsomevariablesinonepartofaprogram,andthenreleasetheallocatedspaceandreturnittothefreestoreonceyouhavefinishedwiththevariablesconcerned.Thememorythenbecomesavailableforreusebyotherdynamicallyallocatedvariableslaterinthesameprogram.Whenyouallocatespaceforavariableusingnew,youarecreatingth

7、evariableinthefreestore.Thevariablecontinuestoexistuntilthememoryitoccupiesisreleasedbytheoperatordelete.DynamicMemoryAllocation5tMynSupposethatweneedspaceforavariableoftypedouble.Wecandefineapointertotypedouble,andthenrequestthatthememoryisa