most important faq in c

7/23/2019 Most Important Faq in c

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MOST IMPORTANT FAQ in C

1. Why would you use a structure

structure is to declare di!!erent data ty"es at a ti#e$ where as a arra y is a %rou" o! relateddata ty"es. the #ain di!!erence &'w structure ( union is in #e#ory re)uire#ent. In

structure s #e#ory is su# o! all the dataty"es declared in it$ where as in union #e#ory is

the one which holds the hi%hest &ytes. struct* int i+!loat %+,+here #e#ory re) is -/0

union*int i+!loat %+,+ here #e#ory re) is only / &ytes

-. 2i!!erence &etween class and structure

There is no #uch di!!erence &etween a class and a structure and the sli%ht

di!!erence is the de!ault sco"e o! class is "ri3ate where as the de!ault sco"e o! structure is%lo&al.

Class is a user de!ined data ty"e in o&4ect oriented "aradi%#. It consists o! &oth

data and code 5#ethods6.where as structure is also a user de!ined data ty"e &ut consists o!

only data #e#&ers. Not #ethods.Structures allow or%ani7ation o! data whereas class allows &oth or%ani7ation o!

data and data security.

8. whats is structure "addin% Say a %i3en structure

Struct*

int a+

char c+

!loat d+,

the si7e o! structure is 9 here. you can control "addin% usin% "ra%#a "ac: why you need "addin% . Ans is you need to ali%n your ;AR accordin% to word &oundary$ "addin% will#a:e your "ro%ra#ne wor: !ast $ I! you don<t ha3e "addin% $ use o! a&o3e struct will %i3e

&us error on so#e #achine. To understand that we need %o throu%h #ore docu#ent on

this

/. what is the di!!erence &etween #ethods and !unction

The #a4or di!!erence &etween #ethods and !unctions is that #ethods called &y there!erence 3aria&les called o&4ects where as the !unctions do not ha3in% any re!erence

3aria&les.

=. What is static #e#ory allocation and dyna#ic #e#ory allocation

Static #e#ory allocation> The co#"iler allocates the re)uired #e#ory s"ace !or adeclared 3aria&le. ?y usin% the address o! o"erator$ the reser3ed address is o&tained and

this address #ay &e assi%ned to a "ointer 3aria&le. Since #ost o! the declared 3aria&le

ha3e static #e#ory$ this way o! assi%nin% "ointer 3alue to a "ointer 3aria&le is :nown as

static #e#ory allocation. Me#ory is assi%ned durin% co#"ilation ti#e.

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in static #e#ory allocation #e#ory is assi%ned at co#"ile ti#e!or

e int arrDE 0 *1$-$8,+ co#"iler will allocate #e#ory !or 8 inte%er at co#"ile.

2yna#ic #e#ory allocation> It uses !unctions such as #alloc5 6 or calloc5 6 to %et#e#ory dyna#ically.I! these !unctions are used to %et #e#ory dyna#ically and the

3alues returned &y these !unctions are assin%ned to "ointer 3aria&les$ such assi%n#ents

are :nown as dyna#ic #e#ory allocation.#e#ory is assined durin% run ti#e.whil in dyna#ic #e#ory allocation #e#ory is assi%ned at run ti#e.

#alloc5-G6 co#"iler will si#"ly see its a !unction and is ar%u#ent. while the

#e#ory will &e allocated at run ti#e.

. What is indirection

I! you declare a 3aria&le$ its na#e is a direct re!erence to its 3alue. I! you ha3e a "ointer to a 3aria&le$ or any other o&4ect in #e#ory$ you ha3e an indirect re!erence to its

3alue.

9. ?etween a lon% "ointer and a char "ointer which one consu#es #ore #e#ory

16 As We All Hnow That Pointer56 Jolds AddressK-6 Address is Always INTLR 5-?ytes6

86 Jence$ -?ytes Are Allocated For Any 2ata Ty"esK

?oth will consu#e sa#e a#ount o! #e#ory. why &ecause they #eans lon% or char "ointer always stores the address o! the character or lon% inte%er.

. Is it &etter to use #alloc56 or calloc56

?oth the #alloc56 and the calloc56 !unctions are used to allocate dyna#ic #e#ory. ach

o"erates sli%htly di!!erent !ro# the other. #alloc56 ta:es a si7e and returns a "ointer to a

chun: o! #e#ory at least that &i%>3oid #alloc5 si7et si7e 6+

calloc56 ta:es a nu#&er o! ele#ents$ and the si7e o! each$ and returns a "ointer to a chun:

o! #e#ory at least &i% enou%h to hold the# all>3oid calloc5 si7et nu#le#ents$ si7et si7eO!le#ent 6+

There<s one #a4or di!!erence and one #inor di!!erence &etween the two !unctions. The

#a4or di!!erence is that #alloc56 doesn<t initiali7e the allocated #e#ory. The !irst ti#e

#alloc56 %i3es you a "articular chun: o! #e#ory$ the #e#ory #i%ht &e !ull o! 7eros. I! #e#ory has &een allocated$ !reed$ and reallocated$ it "ro&a&ly has whate3er 4un: was le!t

in it. That #eans$ un!ortunately$ that a "ro%ra# #i%ht run in si#"le cases 5when #e#ory

is ne3er reallocated6 &ut &rea: when used harder 5and when #e#ory is reused6.calloc56 !ills the allocated #e#ory with all 7ero &its. That #eans that anythin%

there you<re %oin% to use as a char or an int o! any len%th$ si%ned or unsi%ned$ is

%uaranteed to &e 7ero. Anythin% you<re %oin% to use as a "ointer is set to all 7ero &its.That<s usually a null "ointer$ &ut it<s not %uaranteed.Anythin% you<re %oin% to use as a

!loat or dou&le is set to all 7ero &its+ that<s a !loatin%"oint 7ero on so#e ty"es o!

#achines$ &ut not on all.

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The #inor di!!erence &etween the two is that calloc56 returns an array o! o&4ects+

#alloc56 returns one o&4ect. So#e "eo"le use calloc56 to #a:e clear that they want an

array.

. What is a const "ointer

There are cases when you need to de!ine a constant "ointer to a 3aria&le'o&4ect+

!or instance$ when ta:in% a !unction address$ or when you want to "rotect a "ointer !ro#unintended #odi!ications such as assi%n#ent o! new address$ "ointer arith#etic$ etc. In

!act$ an o&4ect<s this is a const"ointer. A constant "ointer is declared>

1G. What is the di!!erence &etween o3erloadin% and o3erridin%

O3erloadin%> &y o3erloadin% a !unction we can use the sa#e !unction !or "er!or#in%

si#ilar o"erations on di!!erent data ty"es.

O3erridin%> &y o3erridin% a !unction we can use the sa#e !unction na#e and "ara#eters

&ut "er!or# di!!erent o"erations on data ty"es.

1. O3erloadin%> It occurs when two #ethods &elon% to sa#e class.

-. O3erridin% occurs when there is inheritance.8. In o3erridin% the si%nature #ust &e sa#e &ut here 4ust the code chan%es.

/. O3erloaded #ethods should di!!er in any one o! the !ollowin% as"ects

a. Nu#&er o! ar%u#ents$

&. Ty"e o! ar%u#ents$c. Order o! ar%u#ents.

11. What is a null "ointer

When re!errin% to co#"uter #e#ory$ a null "ointer is a co##and used to direct a

so!tware "ro%ra# or o"eratin% syste# to an e#"ty location in the co#"uter #e#ory.Co##only$ the null "ointer is used to denote the end o! a #e#ory search or "rocessin%

e3ent. In co#"uter "ro%ra##in%$ a null "ointer is a "ointer that does not "oint to any

o&4ects or !unction. In the "ro%ra##in% lan%ua%e c$ N@@ is an a3aila&le co##and that

can &e used.

1-. "lain the need !or ;irtual 2estructor.

I! &oth the &ase class and deri3ed class can ha3e the constructors$ i! the deri3ed

class is to call the constructor o! its own usin% its o&4ect$ it can &ut when it calls its

destructor$ the co#"iler calls the destructor o! &ase class. That<s why the 3irtualdestructor conce"t is coined. ?ut there are no 3irtual constructors.

18. Jow #any le3els o! "ointers can you ha3e

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The answer de"ends on what you #ean &y le3els o! "ointers. I! you #ean Jow #any

le3els o! indirection can you ha3e in a sin%le declaration the answer is At least 1-.

int i 0 G+int i"G1 0 ( i+

int i"G- 0 ( i"G1+

int i"G8 0 ( i"G-+int i"G/ 0 ( i"G8+

int i"G= 0 ( i"G/+

int i"G 0 ( i"G=+int i"G9 0 ( i"G+

int i"G 0 ( i"G9+

int i"G 0 ( i"G+

int i"1G 0 ( i"G+int i"11 0 ( i"1G+

int i"1- 0 ( i"11+

i"1- 0 1+ ' i 0 1 '

The ANSI C standard says all co#"ilers #ust handle at least 1- le3els. our co#"iler #i%ht su""ort #ore.

1/. what is the di!!erence &etween #alloc and calloc

MALLOC ( )

1. #alloc ta:es only the si7e o! the #e#ory &loc: to &e allocated as in"ut "ara#eter.

-. #alloc allocates #e#ory as a sin%le conti%uous &loc:.

8. i! a sin%le conti%uous &loc: cannot &e allocated then #alloc would !ail.CALLOC ( )

1. calloc ta:es two "ara#eters> the nu#&er o! #e#ory &loc:s and the si7e o! each &loc:

o! #e#ory

-. calloc allocates #e#ory which #ay'#ay not &e conti%uous.8. all the #e#ory &loc:s are initiali7ed to G.

/. it !ollows !ro# "oint - that$ calloc will not !ail i! #e#ory can &eallocated in non

conti%uous &loc:s when a sin%le conti%uous &loc:cannot &e allocated.

1=. Jow do you use a "ointer to a !unction

The hardest "art a&out usin% a "ointerto!unction is declarin% it. Consider an ea#"le.ou want to create a "ointer$ "!$ that "oints to the strc#"56 !unction.

The strc#"56 !unction is declared in this way>

int strc#"5const char $ const char 6To set u" "! to "oint to the strc#"56 !unction$ you want a declaration that loo:s 4ust li:e

the strc#"56 !unction<s declaration$ &ut that has "! rather than strc#">

int 5"!65 const char $ const char 6+A!ter you<3e %otten the declaration o! "!$ you can Uinclude Vstrin%.h and assi%n the

address o! strc#"56 to "!> "! 0 strc#"+

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1 what is the di!!erence &etween !unction "ointer an "ointer to !unction

we can create a "ointer to !unction. so we can call the !unction with that "ointer.e%

let us ta:e two !unctions

3oid su#5int a$int &6+

3oid su&5int a$int &6+

we can create "ointer to these !unctions

3oid 5"65int$int6+

"0su# "58$-6%i3es the su# o! two nu#&ers

"0su& "58$-6 %i3es the di!!erence o! two nu#&ers

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most important faq in c

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