perl_13_references

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1、Chapter13-ReferencesOutline13.1Introduction13.2References13.3ReferencestoNonscalars13.4AnonymousStructures13.5Closures13.6ReferencesasFunctionArguments13.7NestedDataStructures13.8GarbageCollectionandCircularReferences13.9SymbolicReferences13.10Typegl

2、obs13.11ReferencingFilehandles13.12UsesforReferences13.13InternetandWorldWideWebResources13.2ReferencesReferenceIndirectlypointstovalueScalarsthattellprogramwheretofindanothervalueHardReferencesReferdirectlytoavalueinmemoryNotavariableUnarybackslashoperato

3、r()SymbolicReferencesSoftreferencesHoldthenameofthevariabletowhichtheyrefertoFig13_01.pl1#!/usr/bin/perl2#Fig.13.1:fig13_01.pl3#Demonstratescreatinganddereferencingareference.45usestrict;6usewarnings;78my$variable=10;9my$reference=$variable;1011print("$var

4、iable=$variable");12print("$reference=$reference");13print("$$reference=$$reference");14$variable++;15print("$variable=$variable");16print("$reference=$reference");17print("$$reference=$$reference");18$$reference++;19print("$variable=$vari

5、able");20print("$reference=$reference");21print("$$reference=$$reference");$referenceisahardreferencetoscalar$variablePrintsthevaluethatthereferencepointstoAdds1to$variablewillalsoaffectthevalue$referencepointstoAdds1to$$reference,willalsochangetheva

6、lueof$variablePrintsthevalueofthereferencePrintsthevalueof$variableFig13_01.plProgramOutput$variable=10$reference=SCALAR(0x8a31018)$$reference=10$variable=11$reference=SCALAR(0x8a31018)$$reference=11$variable=12$reference=SCALAR(0x8a31018)$$reference=1213.3Re

7、ferencestoNonscalarsNonscalarReferencesSamesyntaxasaareferencetoascalarNestedreferencesTwowaysofdereferencingArrowoperator(->)Witharrays$$reference[element]$reference->[element]@$referenceisusedtoaccessthewholearray13.3ReferencestoNonscalarsWithhashes$$refere

8、nce{‘key’}$reference->{‘key’}%$referenceisusedtoaccessthewholehashDirectdereferencingWithfunctions&$function(arguments)$function->(arguments)Fig13_02.pl1#!/usr/bin/perl2#Fig.13.2:fig13_02