Makefile新手入门：How to write Makefile

I'vealwaysthoughtthiswaseasiertolearnwithadetailedexample,sohere'showIthinkofmakefiles.Foreachsectionyouhaveonelinethat'snotindentedanditshowsthenameofthesectionfollowedbydependencies.Thedependenciescanbeeitherothersections(whichwillberunbeforethecurrentsection)orfiles(whichifupdateswillcausethecurrentsectiontoberunagain).

Here'saquickexample(keepinmindthatI'musing4spaceswhereIshouldbeusingatab,SOwon'tletmeusetabs):

all:a3driver.o g++-oa3drivera3driver.o a3driver.o:a3driver.cpp g++-ca3driver.cpp

Whenyoutype

make

,itwillchoosethefirstsection(all).alldependsona3driver.o,soitwillgotothatsection.a3driver.odependsona3driver.cpp,soitwillonlyrunifa3driver.cpphaschangedsinceitwaslastrun.Assumingithas(orhasneverbeenrun),itwillcompilea3driver.cpptoa.ofile,thengobacktoallandcompilethatintothefileexecutable.

Sincethere'sonlyonefile,itcouldevenbereducedto:

a3driver:a3driver.cpp g++-oa3drivera3driver.cpp

ThereasonIshowedthefirstexampleisthatitshowsthepowerofmakefiles.Ifyouneedtocompileanotherfile,youcanjustaddanothersection.Here'sanexamplewithasecondFile.cpp(whichloadsinaheadernamedsecondFile.h):

all:a3driver.osecondFile.o g++-oa3drivera3driver.osecondFile.o a3driver.o:a3driver.cpp g++-ca3driver.cpp secondFile.o:secondFile.cppsecondFile.h g++-csecondFile.cpp　

ThiswayifyouchangesomethinginsecondFile.cpporsecondFile.handrecompile,itwillonlyrecompilesecondFile.cpp(nota3driver.cpp).Oralternately,ifyouchangesomethingina3driver.cpp,itwon'trecompilesecondFile.cpp.

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Dependencyareatreeofrulesthatlooklikethis:

main_target:source1source2etc commandtobuildmain_targetfromsources source1:dependentsforsource1 commandtobuildsource1　　

Theremustbeablanklineafterthecommandsforatarget,andtheremustnotbeablanklinebeforethecommands.Thefirsttargetinthemakefileistheoverallgoal,othertargetsarebuiltonlyifthefirsttargetdependsonthem.

Soyourmakefilewilllooksomethinglikethis.

a3a.exe:a3driver.obj link/out:a3aa3driver.obj a3driver.obj:a3driver.cpp cca3driver.cpp

　　

PS:HarvestfromStackflow'target='_blank'>http://stackoverflow.com/questions/2481269/how-to-make-simple-c-makefile[/code]