标准c中预定义的宏

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1、[转载]c/c++标准预定义宏2009-08-2214:40http://www.cnblogs.com/sevencat/archive/2004/06/10/14872.html一、标准预定义宏Thestandardpredefinedmacrosarespecifiedbytherelevantlanguagestandards,sotheyareavailablewithallcompilersthatimplementthosestandards.Oldercompilersmaynotprovideallofthem.Theirnamesallstartwithdoubleun

2、derscores.__FILE__Thismacroexpandstothenameofthecurrentinputfile,intheformofaCstringconstant.Thisisthepathbywhichthepreprocessoropenedthefile,nottheshortnamespecifiedin#includeorastheinputfilenameargument.Forexample,"/usr/local/include/myheader.h"isapossibleexpansionofthismacro.__LINE__Thismacroex

3、pandstothecurrentinputlinenumber,intheformofadecimalintegerconstant.Whilewecallitapredefinedmacro,it'saprettystrangemacro,sinceits"definition"changeswitheachnewlineofsourcecode.__FILE__and__LINE__areusefulingeneratinganerrormessagetoreportaninconsistencydetectedbytheprogram;themessagecanstatetheso

4、urcelineatwhichtheinconsistencywasdetected.Forexample,    fprintf(stderr,"Internalerror:"                     "negativestringlength"                     "%dat%s,line%d.",             length,__FILE__,__LINE__);    An#includedirectivechangestheexpansionsof__FILE__and__LINE__tocorrespondtotheincluded

5、file.Attheendofthatfile,whenprocessingresumesontheinputfilethatcontainedthe#includedirective,theexpansionsof__FILE__and__LINE__reverttothevaluestheyhadbeforethe#include(but__LINE__isthenincrementedbyoneasprocessingmovestothelineafterthe#include).A#linedirectivechanges__LINE__,andmaychange__FILE__a

6、swell.SeeLineControl.C99introduces__func__,andGCChasprovided__FUNCTION__foralongtime.Bothofthesearestringscontainingthenameofthecurrentfunction(thereareslightsemanticdifferences;seetheGCCmanual).Neitherofthemisamacro;thepreprocessordoesnotknowthenameofthecurrentfunction.Theytendtobeusefulinconjunc

7、tionwith__FILE__and__LINE__,though.__DATE__Thismacroexpandstoastringconstantthatdescribesthedateonwhichthepreprocessorisbeingrun.Thestringconstantcontainselevencharactersandlookslike"Feb121996".Ifthedayofthemonth