C语言学习第九章(英文版)课件.ppt

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1、Chapter9ThePreprocessor9_1.1Introduction9_1.2The#includePreprocessorDirective9_1.3The#definePreprocessorDirective:SymbolicConstants9_1.4The#definePreprocessorDirective:Macros9_1.5ConditionalCompilationOutlineThe#includePreprocessorDirectiveThe#definePreprocessorDirec

2、tive:SymbolicConstantsKeyPoints9_1.1IntroductionTheroleplayedbyeachprocessorprogramduringthebuildprocess:9_1.1IntroductionPreprocessingOccursbeforeaprogramiscompiledInclusionofotherfilesDefinitionofsymbolicconstantsandmacrosConditionalcompilationofprogramcodeConditio

3、nalexecutionofpreprocessordirectivesFormatofpreprocessordirectivesLinesbeginwith#Onlywhitespacecharactersbeforedirectivesonaline9_1.2The#includePreprocessorDirective#includeCopyofaspecifiedfileincludedinplaceofthedirective#includeSearchesstandardlibraryforf

4、ileUseforstandardlibraryfiles#include"filename"Searchescurrentdirectory,thenstandardlibraryUseforuser-definedfilesUsedfor:ProgramswithmultiplesourcefilestobecompiledtogetherHeaderfile–hascommondeclarationsanddefinitions(classes,structures,functionprototypes)#includes

5、tatementineachfile9_1.2The#includePreprocessorDirective#include#include“file2.c”file1.cAfile3.cC#include“file3.c”file2.cBfile1.cAfile3.cfile2.c9_1.3The#definePreprocessorDirective:SymbolicConstants#definePreprocessordirectiveusedtocreatesymbolicconstantsandmacrosSymb

6、olicconstantsWhenprogramcompiled,alloccurrencesofsymbolicconstantreplacedwithreplacementtextFormat#defineidentifierreplacement-textExample:#definePI3.14159Everythingtorightofidentifierreplacestext#definePI=3.14159Replaces“PI”with"=3.14159"Cannotredefinesymbolicconsta

7、ntsoncetheyhavebeencreated9_1.4The#definePreprocessorDirective:MacrosMacroOperationdefinedin#defineAmacrowithoutargumentsistreatedlikeasymbolicconstantAmacrowithargumentshasitsargumentssubstitutedforreplacementtext,whenthemacroisexpandedPerformsatextsubstitution–noda

8、tatypecheckingThemacro#defineCIRCLE_AREA(x)(PI*(x)*(x))wouldcausearea=CIRCLE_AREA(4);tobecomearea=(3.14159*(4)*(4));9_1.4The#define