An Introduction to GCC读书笔记.docx
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AnIntroductiontoGCC读书笔记
AnIntroductiontoGCC:
fortheGNUCompilersgccandg++读书笔记
Chapter2:
1.CompileaCprogram
a）gcc-Wallhello.c-ohello
i.–Wall:
showallwarning&error.Itisrecommendedthatyoualwaysusethis!
ii.–o:
Thisoptionisusuallygivenasthelastargumentonthecommandline.Ifitisomitted,theoutputiswrittentoadefaultfilecalled‘***.out’.
b）Errordebugging:
i.ThemessagesproducedbyGCCalwayshavetheformfile:
line-number:
message.
2.Compilingmultiplesourcefiles
a）Differencebetween#include"FILE.h"and#include
i.#include"FILE.h"Searchesinthecurrentdirectoryfirstthenthesystemheaderfiledirectory.
ii.#includeonlysearchesinthesystemheaderfiledirectory.
b）gcc-Wallmain.chello_fn.c-onewhello
i.Notethathello.hwillbeincludedautomatically.
3.Compilingfilesindependently
a）Why:
Ifaprogramisstoredinasinglefilethenanychangetoanindividualfunctionrequiresthewholeprogramtoberecompiledtoproduceanewexecutable.
b）Thesourcefilesarecompiledseparatelyandthenlinkedtogether—atwostageprocess.
i.Firststage:
.o,anobjectfile.
ii.Secondstage:
theobjectfilesaremergedtogetherbyaseparateprogramcalledthelinker.
c）Creatingobjectfilesfromsourcefiles
i.gcc-Wall-cmain.c
-c:
compileasourcefileintoanobjectfile
ii.Containingthemachinecodeforthemainfunction,hasanexternalreferencetohello（）,buttheexactmemoryaddressisnotdecided.
iii.Noneedtoadd–ooption
iv.Noneedtoputtheheaderfile‘hello.h’onthecommandline,
d）Creatingexecutablesfromobjectfiles
i.gccmain.ohello_fn.o-ohello
ii.Noneedtousethe‘-Wall’warningoption:
filehasbeencompiled.
iii.Failsonlyiftherearereferenceswhichcannotberesolved
e）Linkorderofobjectfiles
i.gccmain.ohello_fn.o-ohello
ii.Objectfilewhichcontainsthedefinitionofafunctionshouldappearafteranyfileswhichcallthatfunction.
f）Recompilingandrelinking
i.Iftheprototypeofafunctionhaschanged,itisnecessarytomodifyandrecompilealloftheothersourcefileswhichuseit.
ii.Linkingisfasterthancompilation
g）Linkingwithexternallibraries
i.Themostcommonuseoflibrariesistoprovidesystemfunctions.
ii.Librariesaretypicallystoredinspecialarchivefileswiththeextension‘.a’,referredtoasstaticlibraries
iii.Usingarcommandtocreateastaticlibrary
iv.Thedefaultlibraryfileislib.a,whenwereferredotherfunction,suchasmath.h,wewillneedlibm.a
v.gcc-Wallcalc.c-lm-ocalc
vi.Thecompileroption‘-lNAME’willattempttolinkobjectfileswithalibraryfile‘libNAME.a’inthestandardlibrarydirectories.
h）Linkorderoflibraries
i.Containingthedefinitionofafunctionshouldappearafteranysourcefilesorobjectfileswhichuseit.
ii.Alibrarywhichcallsanexternalfunctiondefinedinanotherlibraryshouldappearbeforethelibrarycontainingthefunction.
iii.gcc-Walldata.c-lglpk-lmlibglpk.acallsfunctionsinlibm.a
i）Usinglibraryheaderfile:
Ifyouwronglyomittheincludeheaderfile,youcanonlydetectthiserrorby–Wall
Chapter3:
compilationoptions
1.Settingsearchpaths
a）Bydefault,gccsearches
i.Thefollowingdirectoriesforheaderfiles:
1./usr/local/include/
2./usr/include/
ii.Thefollowingdirectoriesforlibraries:
1./usr/local/lib/
2./usr/lib/
iii.Aheaderfilefoundin‘/usr/local/include’takesprecedenceoverafilewiththesamenamein‘/usr/include’.
iv.Thecompileroptions‘-I’and‘-L’addnewdirectoriestothebeginningoftheincludepathandlibrarysearchpathrespectively.
b）Searchpathexample
i.gcc-Wall-I/opt/gdbm-1.8.3/include-L/opt/gdbm-1.8.3/libdbmain.c–lgdbm
-I:
addnewdirectorytotheheaderfilesearchset.
-L:
addnewdirectorytothelibrarysearchset.
ii.Youshouldneverplacetheabsolutepathsofheaderfilesin#includestatementsinyoursourcecode,asthiswillpreventtheprogramfromcompilingonothersystems
c）Environmentvariables
i.Setin.bash_profile
ii.AdditionaldirectoriescanbeaddedtotheincludepathusingtheenvironmentvariableC_INCLUDE_PATH（forCheaderfiles）orCPLUS_INCLUDE_PATH（forC++headerfiles）.
iii.C_INCLUDE_PATH=/opt/gdbm-1.8.3/include
C_INCLUDE_PATH=.:
/opt/gdbm-1.8.3/include:
/net/include
exportC_INCLUDE_PATH
LIBRARY_PATH=/opt/gdbm-1.8.3/lib
exportLIBRARY_PATH
d）Extendedsearchpaths
i.gcc-I.-I/opt/gdbm-1.8.3/include-I/net/include-L.-L/opt/gdbm-1.8.3/lib-L/net/lib
Addmultiplesearchpaths
e）Exactsearchorder.
i.Command-lineoptions‘-I’and‘-L’,fromlefttoright
ii.Directoriesspecifiedbyenvironmentvariables,suchasC_INCLUDE_PATHandLIBRARY_PATH
iii.Defaultsystemdirectories
2.Sharedlibrariesandstaticlibraries
a）Staticlibraries
i.‘.a’files
ii.Whenaprogramislinkedagainstastaticlibrary,themachinecodefromtheobjectfilesforanyexternalfunctionsusedbytheprogramiscopiedfromthelibraryintothefinalexecutable
b）Sharedlibraries
i.extension‘.so’
ii.Anexecutablefilelinkedagainstasharedlibrarycontainsonlyasmalltableofthefunctionsitrequires.
iii.Beforetheexecutablefilestartsrunning,themachinecodefortheexternalfunctionsiscopiedintomemoryfromthesharedlibraryfileondiskbytheoperatingsystem
iv.Dynamiclinkingmakesexecutablefilessmallerandsavesdiskspace,becauseonecopyofalibrarycanbesharedbetweenmultipleprograms.
v.Sharedlibrariesmakeitpossibletoupdatealibrarywithoutrecompilingtheprogramswhichuseit
c）gcccompilesprogramstousesharedlibrariesbydefaultonmostsystems,iftheyareavailable
d）Bydefaulttheloadersearchesforsharedlibrariesonlyinapredefinedsetofsystemdirectories,suchas‘/usr/local/lib’and‘/usr/lib
e）LD_LIBRARY_PATH=/opt/gdbm-1.8.3/lib
exportLD_LIBRARY_PATH
f）gcc-Wall-static-I/opt/gdbm-1.8.3/include/-L/opt/gdbm-1.8.3/lib/dbmain.c-lgdbm-static:
forcestaticlinking
g）gcc-Wall-I/opt/gdbm-1.8.3/includedbmain.c/opt/gdbm-1.8.3/lib/libgdbm.so
Linkdirectlywithindividuallibraryfilesbyspecifyingthefullpathtothelibraryonthecommandline
3.Clanguagestandards
a）ANSI/ISO
i.gcc-Wall-ansiansi.c
-ansi:
useansi.ThisallowsprogramswrittenforANSI/ISOCtobecompiledwithoutanyunwantedeffectsfromGNUextensions.
b）StrictANSI/ISO
i.gcc-Wall-ansi-pedanticgnuarray.c
-pedantic:
gcctorejectallGNUCextensions,notjustthosethatareincompatiblewiththeANSI/ISOstandard.
ii.ThishelpsyoutowriteportableprogramswhichfollowtheANSI/ISOstandard.
c）Selectingspecificstandards
i.‘-std=c89’or‘-std=iso9899:
1990’
Std9899
ii.‘-std=iso9899:
199409
Addinternationalizationsupport:
language
iii.‘-std=c99’or‘-std=iso9899:
1999’
Std99
iv.‘-std=gnu89’and‘-std=gnu99’.clanguagestandard+GNUextension
d）Warningoptionsin–Wall
i.‘-Wcomment’（includedin‘-Wall’）
Thisoptionwarnsaboutnestedcomments.
ii.‘-Wformat’（includedin‘-Wall’）
Thisoptionwarnsabouttheincorrectuseofformatstringsinfunctionssuchasprintfandscanf,wheretheformatspecifierdoesnotagreewiththetypeofthecorrespondingfunctionargument.
iii.‘-Wunused’（includedin‘-Wall’）Thisoptionwarnsaboutunusedvariables.
iv.‘-Wimplicit’（includedin‘-Wall’）
Thisoptionwarnsaboutanyfunctionsthatareusedwithoutbeingdeclared.Themostcommonreasonforafunctiontobeusedwithoutbeingdeclaredisforgettingtoincludeaheaderfile.
v.‘-Wreturn-type’（includedin‘-Wall’）
Thisoptionwarnsaboutfunctionsthataredefinedwithoutareturntypebutnotdeclaredvoid.
e）Additionalwarningoptions
i.Theyarenotincludedin‘-Wall’becausetheyonlyindicatepossiblyproblematicor“suspicious”code
ii.Itismoreappropriatetousethemperiodicallyandreviewtheresults,checkingforanythingunexpected,ortoenablethemforsomeprogramsorfiles.
iii.‘-W’
Thisisageneraloptionsimilarto‘-Wall’whichwarnsaboutaselectionofcommonprogrammingerrors
Inpractice,theoptions‘-W’and‘-Wall’arenormallyusedtogether.
iv.‘-Werror’
Changesthedefaultbehaviorbyconvertingwarningsintoerrors,stoppingthecompilationwheneverawarningoccurs.
v.‘-Wconversion’
Thisoptionwarnsaboutimplicittypeconversionsthatcouldcauseunexpectedresults.Forexample:
unsignedintx=-1;
vi.‘-Wshadow’
Thisoptionwarnsabouttheredeclarationofavariablenameinascopewhereithasalreadybeendeclared.
vii.‘-Wcast-qual’
Thisoptionwarnsaboutpointersthatarecasttoremoveatypequalifier,suchasconst.
viii.-Wtraditional’
ThisoptionwarnsaboutpartsofthecodewhichwouldbeinterpreteddifferentlybyanANSI/ISOcompileranda“traditional”pre-ANSIcompiler.
Chapter4:
Usingthepreprocessor
1.Definingmacros
a）gcc-Wall-DTESTdtest.c
-DTEST:
defineamacrocalledTESTandassign1asitsvalue.
Thegccoption‘-DNAME’definesapreprocessormacroNAMEfromthecommandline.
2.Originofthemacros
a）Specifiedonthecommandlinewiththeoption‘-D’,
b）Inasourcefile（orlibraryheaderfile）with#define.
c）Automaticallydefinedbythecompiler—thesetypicallyuseareservednamespacebeginningwithadouble-underscoreprefix‘__’.
3.Macroswithvalues
a）Thisvalueisinsertedintothesourcecodeateachpointwherethemacrooccurs
b）Notethatmacrosarenotexpandedinsidestrings
c）gcc-Wall-DNUM=100dtestval.c
The‘-D’command-lineoptioncanbeusedintheform‘-DNAME=VALUE’.
d）Notethatitisagoodideatosurroundmacrosbyparentheseswhenevertheyarepartofanexpression.
e）Amacrocanbedefinedtoaemptyvalueusingquotesonthecommandline,-DNAME=""
4.Preprocessingsourcefiles
a）gcc-Etest.c-Eoption:
U
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