Functions Pointers in C Programming with Examples - Guru99

Pointers give greatly possibilities to 'C' functions which we are limited to return one value. With pointer parameters, our functions now ... Skiptocontent Pointersgivegreatlypossibilitiesto‘C’functionswhichwearelimitedtoreturnonevalue.Withpointerparameters,ourfunctionsnowcanprocessactualdataratherthanacopyofdata. Inordertomodifytheactualvaluesofvariables,thecallingstatementpassesaddressestopointerparametersinafunction. Inthistutorial,youwilllearn- FunctionsPointersExample FunctionswithArrayParameters FunctionsthatReturnanArray FunctionPointers ArrayofFunctionPointers FunctionsUsingvoidPointers FunctionPointersasArguments FunctionsPointersExample Forexample,thenextprogramswapstwovaluesoftwo: voidswap(int*a,int*b); intmain(){ intm=25; intn=100; printf("mis%d,nis%d\n",m,n); swap(&m,&n); printf("mis%d,nis%d\n",m,n); return0;} voidswap(int*a,int*b){ inttemp; temp=*a; *a=*b; *b=temp;} } Output: mis25,nis100 mis100,nis25 Theprogramswapstheactualvariablesvaluesbecausethefunctionaccessesthembyaddressusingpointers.Herewewilldiscusstheprogramprocess: Wedeclarethefunctionresponsibleforswappingthetwovariablevalues,whichtakestwointegerpointersasparametersandreturnsanyvaluewhenitiscalled. Inthemainfunction,wedeclareandinitializetwointegervariables(‘m’and‘n’)thenweprinttheirvaluesrespectively. Wecalltheswap()functionbypassingtheaddressofthetwovariablesasargumentsusingtheampersandsymbol.Afterthat,weprintthenewswappedvaluesofvariables. Herewedefinetheswap()functioncontentwhichtakestwointegervariableaddressesasparametersanddeclareatemporaryintegervariableusedasathirdstorageboxtosaveoneofthevaluevariableswhichwillbeputtothesecondvariable. Savethecontentofthefirstvariablepointedby‘a’inthetemporaryvariable. Storethesecondvariablepointedbybinthefirstvariablepointedbya. Updatethesecondvariable(pointedbyb)bythevalueofthefirstvariablesavedinthetemporaryvariable. FunctionswithArrayParameters InC,wecannotpassanarraybyvaluetoafunction.Whereas,anarraynameisapointer(address),sowejustpassanarraynametoafunctionwhichmeanstopassapointertothearray. Forexample,weconsiderthefollowingprogram: intadd_array(int*a,intnum_elements); intmain(){ intTab[5]={100,220,37,16,98}; printf("Totalsummationis%d\n",add_array(Tab,5)); return0;} intadd_array(int*p,intsize){ inttotal=0; intk; for(k=0;k int*build_array(); intmain(){ int*a; a=build_array();/*getfirst5evennumbers*/ for(k=0;k<5;k++) printf("%d\n",a[k]); return0;} int*build_array(){ staticintTab[5]={1,2,3,4,5}; return(Tab);} Output: 1 2 3 4 5 Andhere,wewilldiscusstheprogramdetails Wedefineanddeclareafunctionwhichreturnsanarrayaddresscontaininganintegervalueanddidn’ttakeanyarguments. Wedeclareanintegerpointerwhichreceivesthecompletearraybuiltafterthefunctioniscalledandweprintitscontentsbyiteratingtheentirefiveelementarray. Noticethatapointer,notanarray,isdefinedtostorethearrayaddressreturnedbythefunction.Alsonoticethatwhenalocalvariableisbeingreturnedfromafunction,wehavetodeclareitasstaticinthefunction. FunctionPointers Asweknowbydefinitionthatpointerspointtoanaddressinanymemorylocation,theycanalsopointtoatthebeginningofexecutablecodeasfunctionsinmemory. Apointertofunctionisdeclaredwiththe*,thegeneralstatementofitsdeclarationis: return_type(*function_name)(arguments) Youhavetorememberthattheparenthesesaround(*function_name)areimportantbecausewithoutthem,thecompilerwillthinkthefunction_nameisreturningapointerofreturn_type. Afterdefiningthefunctionpointer,wehavetoassignittoafunction.Forexample,thenextprogramdeclaresanordinaryfunction,definesafunctionpointer,assignsthefunctionpointertotheordinaryfunctionandafterthatcallsthefunctionthroughthepointer: #include voidHi_function(inttimes);/*function*/ intmain(){ void(*function_ptr)(int);/*functionpointerDeclaration*/ function_ptr=Hi_function;/*pointerassignment*/ function_ptr(3);/*functioncall*/ return0;} voidHi_function(inttimes){ intk; for(k=0;k intsum(intnum1,intnum2); intsub(intnum1,intnum2); intmult(intnum1,intnum2); intdiv(intnum1,intnum2); intmain() {intx,y,choice,result; int(*ope[4])(int,int); ope[0]=sum; ope[1]=sub; ope[2]=mult; ope[3]=div; printf("Entertwointegernumbers:"); scanf("%d%d",&x,&y); printf("Enter0tosum,1tosubtract,2tomultiply,or3todivide:"); scanf("%d",&choice); result=ope[choice](x,y); printf("%d",result); return0;} intsum(intx,inty){return(x+y);} intsub(intx,inty){return(x-y);} intmult(intx,inty){return(x*y);} intdiv(intx,inty){if(y!=0)return(x/y);elsereturn0;} Entertwointegernumbers:1348 Enter0tosum,1tosubtract,2tomultiply,or3todivide:2 624 Here,wediscusstheprogramdetails: Wedeclareanddefinefourfunctionswhichtaketwointegerargumentsandreturnanintegervalue.Thesefunctionsadd,subtract,multiplyanddividethetwoargumentsregardingwhichfunctionisbeingcalledbytheuser. Wedeclare4integerstohandleoperands,operationtype,andresultrespectively.Also,wedeclareanarrayoffourfunctionpointer.Eachfunctionpointerofarrayelementtakestwointegersparametersandreturnsanintegervalue. Weassignandinitializeeacharrayelementwiththefunctionalreadydeclared.Forexample,thethirdelementwhichisthethirdfunctionpointerwillpointtomultiplicationoperationfunction. Weseekoperandsandtypeofoperationfromtheusertypedwiththekeyboard. Wecalledtheappropriatearrayelement(Functionpointer)witharguments,andwestoretheresultgeneratedbytheappropriatefunction. Theinstructionint(*ope[4])(int,int);definesthearrayoffunctionpointers.Eacharrayelementmusthavethesameparametersandreturntype. Thestatementresult=ope[choice](x,y);runstheappropriatefunctionaccordingtothechoicemadebytheuserThetwoenteredintegersaretheargumentspassedtothefunction. FunctionsUsingvoidPointers Voidpointersareusedduringfunctiondeclarations.Weuseavoid*returntypepermitstoreturnanytype.Ifweassumethatourparametersdonotchangewhenpassingtoafunction,wedeclareitasconst. Forexample: void*cube(constvoid*); Considerthefollowingprogram: #include void*cube(constvoid*num); intmain(){ intx,cube_int; x=4; cube_int=cube(&x); printf("%dcubedis%d\n",x,cube_int); return0;} void*cube(constvoid*num){ intresult; result=(*(int*)num)*(*(int*)num)*(*(int*)num); returnresult;} Result: 4cubedis64 Here,wewilldiscusstheprogramdetails: Wedefineanddeclareafunctionthatreturnsanintegervalueandtakesanaddressofunchangeablevariablewithoutaspecificdatatype.Wecalculatethecubevalueofthecontentvariable(x)pointedbythenumpointer,andasitisavoidpointer,wehavetotypecastittoanintegerdatatypeusingaspecificnotation(*datatype)pointer,andwereturnthecubevalue. Wedeclaretheoperandandtheresultvariable.Also,weinitializeouroperandwithvalue“4.” Wecallthecubefunctionbypassingtheoperandaddress,andwehandlethereturningvalueintheresultvariable FunctionPointersasArguments Anotherwaytoexploitafunctionpointerbypassingitasanargumenttoanotherfunctionsometimescalled“callbackfunction”becausethereceivingfunction“callsitback.” Inthestdlib.hheaderfile,theQuicksort“qsort()”functionusesthistechniquewhichisanalgorithmdedicatedtosortanarray. voidqsort(void*base,size_tnum,size_twidth,int(*compare)(constvoid*,constvoid*)) void*base:voidpointertothearray. size_tnum:Thearrayelementnumber. size_twidthTheelementsize. int(*compare(constvoid*,constvoid*):functionpointercomposedoftwoargumentsandreturns0whentheargumentshavethesamevalue,<0whenarg1comesbeforearg2,and>0whenarg1comesafterarg2. Thefollowingprogramsortsanintegersarrayfromsmalltobignumberusingqsort()function: #include #include intcompare(constvoid*,constvoid*); intmain(){ intarr[5]={52,14,50,48,13}; intnum,width,i; num=sizeof(arr)/sizeof(arr[0]); width=sizeof(arr[0]); qsort((void*)arr,num,width,compare); for(i=0;i<5;i++) printf("%d",arr[i]); return0;} intcompare(constvoid*elem1,constvoid*elem2){ if((*(int*)elem1)==(*(int*)elem2))return0; elseif((*(int*)elem1)0whenarg1comesafterarg2.Theparametersareavoidpointerstypecastedtotheappropriatearraydatatype(integer) WedefineandinitializeanintegerarrayThearraysizeisstoredinthenumvariableandthesizeofeacharrayelementisstoredinwidthvariableusingsizeof()predefinedCoperator. Wecalltheqsortfunctionandpassthearrayname,size,width,andcomparisonfunctiondefinedpreviouslybytheuserinordertosortourarrayinascendingorder.Thecomparisonwillbeperformedbytakingineachiterationtwoarrayelementsuntiltheentirearraywillbesorted. Weprintthearrayelementstobesurethatourarrayiswellsortedbyiteratingtheentirearrayusingforloop. YouMightLike: CTutorialforBeginners:LearnCProgrammingLanguageBasics CConditionalStatement:IF,IFElseandNestedIFElsewithExample LoopsinC:For,While,DoWhileloopingStatements[Examples] Differencebetweenstrlen()andsizeof()forstringinC 20+BestCIDEforWindows,Mac&Linux(2022Editors) Postnavigation ReportaBug Previous PrevNextContinue Scrolltotop ToggleMenuClose Searchfor: Search