嵌入式面试问题及解答英文Word格式文档下载.docx

嵌入式面试问题及解答英文Word格式文档下载.docx

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{

c5=c4=analysis;

++c4;

c3=&

analysis[6];

c2=c5+2;

c1=&

analysis[7]-3;

printf（"

%c\t%c\t%c\t%c\t%c"

*c1,*c2,*c3,*c4,*c5）;

return0;

}

c1,c2,c3,c4andc5arepointers（whichcanholdaddresses）.

analysisisanarrayvariablewhichisholdingthestring"

analysis"

.

>

Thestartingaddressofthearrayisgiventoc5andc4.Hencetheypointtofirstcharacter'

inthearray.

c4isincrementedby1.Hencepointsto'

c3isgiventheaddressof7thcharacter（countfrom0）ofthearray.Hencec3pointstocharacter'

c5pointstofirstcharacter.plus2means,c2pointsto3rdcharacter'

（second'

inthestring）.

c1pointsto3rdcharacterfromtheend（notcountingthelastcharacter）.

c1holdstheaddress.*c1meansthedatastroredatc1.Sincec1pointsto3rdcharacterfromtheend（thatis5thcharacter-countstartsfrom0）,*choldscharacter'

Hence*c1willprint'

onthescreen.

Similarlyforotherpointervariables*c2,*c3,*c4and*c5

3.

a=5b=10c=7

（a>

c）?

a:

（（b>

b:

c）

Answer:

10

4

Question:

HowdoyoudeclareanarrayofNpointerstofunctionsreturning

pointerstofunctionsreturningpointerstocharacters?

A.char*（*（*a[N]）（））（）;

B.Buildthedeclarationupincrementally,usingtypedefs:

C.Usethecdeclprogram,whichturnsEnglishintoCandvice

versa:

D.Alloftheabove.

Answer:

D

5

voidmain（）

{

intcount=10,*temp,sum=0;

temp=&

count;

*temp=20;

sum;

*temp=count;

printf（"

%d%d%d"

count,*temp,sum）;

}

Answer:

20;

6

inti=7;

%d"

i++*i++）;

49.

Note:

Don’tchangeavariabletwiceinoneexpression.

7

Thenumberofsyntaxerrorsintheprogram?

intf（）

f

（1）;

f（1,2）;

f（1,2,3）;

f（inti,intj,intk）

%d%d%d"

i,j,k）;

None.

8

voidmain（）

floatj;

j=1000*1000;

%f"

j）;

A.1000000

B.Overflow

C.Error

D.Noneoftheabove

9

Givetheoutputoftheprogram

unsignedi=1;

/*unsignedchark=-1=>

k=255;

*/

signedj=-1;

/*chark=-1=>

k=65535*/

/*unsignedorsignedintk=-1=>

k=65535*/

if（i<

j）

less"

）;

else

if（i>

greater"

if（i==j）

equal"

less

10

Givetheoutputoftheprogram

char*s="

12345sn"

;

sizeof（s））;

4

11

inti;

for（i=1;

i<

4,i++）

switch（i）

case1:

printf（"

i）;

break;

case2:

case3:

switch（i）case4:

1,2,3,4

12.

Howtopasstwoargumentstoafunctionpromptedtobyfunctionpointer

A.g->

（1,2）

B.*g（1,2）

C.（*g）（1,2）

D.g（1,2）

C

13

Canyouhaveconstantvolatilevariable?

YES.Wecanhaveaconstvolatilevariable.

avolatilevariableisavariablewhichcanbechangedbytheextrenalevents（likeaninterrputtimerswillincrementthevoltilevarible.Ifyoudontwantyouvolatilevaribaletobechangedthendeclarethemas“constvolatile”.

14.

studythecode:

#include<

stdio.h>

constinta=100;

int*p;

p=&

a;

（*p）++;

a=%d\n（*p）=%d\n"

a,*p）;

Whatisprinted?

A）100,101B）100,100C）101,101D）Noneoftheabove

AnswerC

EmbeddedC

1.Usingthe#definestatement,howwouldyoudeclareamanifestconstantthatreturnsthenumberofsecondsinayear?

Disregardleapyearsinyouranswer.

#defineSECONDS_PER_YEAR（60*60*24*365）UL

I'

mlookingforseveralthingshere:

Basicknowledgeofthe#definesyntax（forexample,nosemi-colonattheend,theneedtoparenthesize,andsoon）

Anunderstandingthatthepre-processorwillevaluateconstantexpressionsforyou.Thus,itisclearer,andpenalty-free,tospellouthowyouarecalculatingthenumberofsecondsinayear,ratherthanactuallydoingthecalculationyourself

Arealizationthattheexpressionwilloverflowanintegerargumentona16-bitmachine-hencetheneedfortheL,tellingthecompilertotreatthevariableasaLong

Asabonus,ifyoumodifiedtheexpressionwithaUL（indicatingunsignedlong）,thenyouareofftoagreatstart.Andremember,firstimpressionscount!

2.Writethe"

standard"

MINmacro-thatis,amacrothattakestwoargumentsandreturnsthesmallerofthetwoarguments.

#defineMIN（A,B）（（A）<

=（B）?

（A）:

（B））

Thepurposeofthisquestionistotestthefollowing:

Basicknowledgeofthe#definedirectiveasusedinmacros.ThisisimportantbecauseuntiltheinlineoperatorbecomespartofstandardC,macrosaretheonlyportablewayofgeneratinginlinecode.Inlinecodeisoftennecessaryinembeddedsystemsinordertoachievetherequiredperformancelevel

Knowledgeoftheternaryconditionaloperator.ThisoperatorexistsinCbecauseitallowsthecompilertoproducemoreoptimalcodethananif-then-elsesequence.Giventhatperformanceisnormallyanissueinembeddedsystems,knowledgeanduseofthisconstructisimportant

Understandingoftheneedtoverycarefullyparenthesizeargumentstomacros

Ialsousethisquestiontostartadiscussiononthesideeffectsofmacros,forexample,whathappenswhenyouwritecodesuchas:

least=MIN（*p++,b）;

3.Infiniteloopsoftenariseinembeddedsystems.HowdoesyoucodeaninfiniteloopinC?

Thereareseveralsolutionstothisquestion.Mypreferredsolutionis:

while

（1）

?

5.Usingthevariablea,givedefinitionsforthefollowing:

a）Aninteger

b）Apointertoaninteger

c）Apointertoapointertoaninteger

d）Anarrayof10integers

e）Anarrayof10pointerstointegers

f）Apointertoanarrayof10integers

g）Apointertoafunctionthattakesanintegerasanargumentandreturnsaninteger

h）Anarrayoftenpointerstofunctionsthattakeanintegerargumentandreturnaninteger

Answers:

a）inta;

//Aninteger

b）int*a;

//Apointertoaninteger

c）int**a;

//Apointertoapointertoaninteger

d）inta[10];

//Anarrayof10integers

e）int*a[10];

//Anarrayof10pointerstointegers

f）int（*a）[10];

//Apointertoanarrayof10integers

g）int（*a）（int）;

//Apointertoafunctionathattakesanintegerargumentandreturnsaninteger

h）int（*a[10]）（int）;

//Anarrayof10pointerstofunctionsthattakeanintegerargumentandreturnaninteger

Peopleoftenclaimthatacoupleofthesearethesortsofthingthatonelooksupintextbooks-andIagree.Whilewritingthisarticle,Iconsultedtextbookstoensurethesyntaxwascorrect.However,Iexpecttobeaskedthisquestion（orsomethingclosetoit）whenI'

mbeinginterviewed.Consequently,ImakesureIknowtheanswers,atleastforthefewhoursoftheinterview.Candidateswhodon'

tknowalltheanswers（oratleastmostofthem）aresimplyunpreparedfortheinterview.Iftheycan'

tbepreparedfortheinterview,whatwilltheybepreparedfor?

6.Whataretheusesofthekeywordstatic?

StatichasthreedistinctusesinC:

Avariabledeclaredstaticwithinthebodyofafunctionmaintainsitsvaluebetweenfunctioninvocations

Avariabledeclaredstaticwithinamodule,（butoutsidethebodyofafunction）isaccessiblebyallfunctionswithinthatmodule.Itisnotaccessiblebyfunctionswithinanyothermodule.Thatis,itisalocalizedglobal

Functionsdeclaredstaticwithinamodulemayonlybecalledbyotherfunctionswithinthatmodule.Thatis,thescopeofthefunctionislocalizedtothemodulewithinwhichitisdeclared

Mostcandidatesgetthefirstpartcorrect.Areasonablenumbergetthesecondpartcorrect,whileapitifulnumberunderstandthethirdanswer.Thisisaseriousweaknessinacandidate,sinceheobviouslydoesn'

tunderstandtheimportanceandbenefitsoflocalizingthescopeofbothdataandcode.

7.Whatdothefollowingdeclarationsmean?

constinta;

intconsta;

constint*a;

int*consta;

intconst*consta;

Answer

Thefirsttwomeanthesamething,namelyaisaconst（read-only）integer.Thethirdmeansaisapointertoaconstinteger（thatis,theintegerisn'

tmodifiable,butthepointeris）.Thefourthdeclaresatobeaconstpointertoaninteger（thatis,theintegerpointedtobyaismodifiable,butthepointerisnot）.Thefinaldeclarationdeclaresatobeaconstpointertoaconstinteger（thatis,neithertheintegerpointedtobya,northepointeritselfmaybemodified）.

8.Whatdoesthekeywordvolatilemean?

Givethreedifferentexamplesofitsuse.

Avolatilevariableisonethatcanchangeunexpectedly.Consequently,thecompilercanmakenoassumptionsaboutthevalueofthevariable.Inparticular,theoptimizermustbecarefultoreloadthevariableeverytimeitisusedinsteadofholdingacopyinaregister.Examplesofvolatilevariablesare:

Hardwareregistersinperipherals（forexample,statusregisters）

Non-automaticvariablesreferencedwithinaninterruptserviceroutine

Variablessharedbymultipletasksinamulti-threadedapplication

9.

Canapointerbevolatile?

Explain.