Advanced Use of Pointers. CS2023 Winter 2004

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1 Advancd Us f Pintrs CS2023 Wintr 2004

2 Outcms: Advancd us f Pintrs C fr Java Prgrammrs, Chaptr 8, sctin 8.11, 8.15 Othr txtbks n C n rsrv Aftr th cnclusin f this sctin yu shuld b abl t Allcat and dallcat blcks f mmry dynamically n th had Us pintrs t functins in rdr t pass a functin as a paramtr t anthr functin Us gnric pintrs t rit mr gnral functins

3 Dynamic Mmry Allcatin C's data structurs nrmally fixd in siz C supprts dynamic mmry allcatin t allcat strag during xcutin ndd fr dynamic arrays, lists, strings,... Dynamically allcatd mmry strd n th hap

4 Rcall: Mmry Managmnt Dynamically allcatd variabls Mmry allcatd and dstryd at run tim, undr cntrl f prgrammr! N guarant that first variabl t b dstryd is last cratd This ara f mmry can hav hls and is calld th hap

5 Rcall: Mmry Managmnt Usually hap and stack bgin at ppsit nds f th prgram's mmry, and gr tards ach thr

6 !!!!!! * #. ',, #, + Dynamic Mmry Allcatin Allcats a blck f mmry, but dsn't initializ it Allcats a blck f mmry and clars it and f typ, hich is typ rturnd by sizf pratr (nrmally ) " Nt: argumnts f $&% ')( $

7 2 < E 2 < < : I J : 80 6 J G Dynamic Mmry Allcatin T primary mthds f allcating mmry: C&D < 1&; 1&; 9 : 354 :< 0 / <)= 1&; 9 : HG F A :< 0 / <)= C&D < 1&; :< 1&; <)= D 35J C D C I 9 L 0 < 1 ; 9 :?M 0 4 K C&D C I 9 L 0 < 1&; 9N 8 K u shuld alays rmmbr t chck if a call t a mmry allcatin functin as succssful.

8 Dynamic Mmry Allcatin OP RS T U R V XW Z [ ] ^ P ^ O P R U O _` ` S a cb X X Z ` Od ^ _` O P a a gf h h ^i O ` kj ml n V l gh p j T R S a q r T OP Rs T U R c XW Z [ ] ^ t O P R U O _` ` s a cb X X Z ` t R Od ^ _` O P a a gf h h ^i O ` kj ml n V l gh p j T R s a u T 5 s

9 v ~ ƒ { } zy x Œ Š Ž Œ Š ˆ ~ ƒ v ~ ƒ { } zy ~œ { } zy Dynamic Mmry Allcatin Nt that mallc rturns vid*, hras th lft hand sid f is f typ. Sm prgrammrs us an xplicit cast, but this is nt rquird: { ~ & Š Alays pass rathr than th abslut valu us { { ~ š as a paramtr t mallc, instad f

10 Ÿ Ÿ ª ¹ µ ³ Ÿ ² Ã Ë Á Ã ÇÁ ÂÁ À À Mmry Dallcatin Mmry shuld b dallcatd nc th task it as allcatd fr has bn cmpltd. ž ± ± ž «³ º ± µ ¼» ½ ½ ½ ¾ É Â È Í Ì É&Ê È Å Æ Ä

11 Ñ Ð Ï Ï Î Ô Ó Ò Mmry Dallcatin Alays fll th call t ith Ô

12 ÚÙ Ø Ø Õ ÚÙ Ý ß ÜÛ â ç à é æ è î ì ì ç ï ð ø ý õ ÿ öü ôó ñ ò ø ý õ ÿ öü ôó ñ ò Errrs Mmry dallcatin using shuld nly b usd if mmry has bn prviusly allcatd ith : Ý Þ Ö& åæ ç àäã àá í æ êë alays rmmbr hr mmry cam frm: hap r stack Dn't crat garbag bjcts! úþ úû øù õö úþ úû øù õö Th first bjct cratd is n inaccssibl

13 Errrs Givn t pintrs and, th assignmnt nt cpy th blck f mmry pintd t by blck f mmry pintd t by ds int a Rmmbr that aftr if yu call yu must nt call ; and shar th valu; this uld als dallcat, n

14 ! Pintrs t lcks Cntaining Pintrs A blck cntaining thr pintrs t dubl bjcts. In rdr t accss a singl bjct, th cd has t apply drfrncing tic blck

15 Pintrs t lcks Cntaining Pintrs "$# % '& ( ) ) '& # * +,. " ( /0 1 ( / '& # * +98 :* ' ' # * ; < 0 = #( / "$# % '& ( ) 8 A A C C CD E FHG I KJ L MON K P R TS N K U U V K F J WJ X G [Z K L ] X X G J^ _ ` K a Gb F cj G d W X b V V V L L f g g V ih i ij k l m l n qp sr t uv x k n qp yr z y{ z { t uv x k

16 ˆ ~ ƒ Œ Š Ž } ƒ œ š «š Pintrs t lcks Cntaining Pintrs Th cmplt cd t initializ th blck: Š Š ƒ } T fr mmry : žÿ œ œ ª œ œ

17 ± ²³ µ ¹ º» ¼¾½ ³ À Á Â ½ Ã Â±Ä Å Æ Ä ² Ç ÄÇ ½ È» º ³ ²É É Ã Â Ä Å ÆËÊ Å Â Â Ä Å É µ Ì Í ³ Î Ä ²É Ä Á Ã Â» Ï Ï Ï Ê Ê ÑÐ Ò Ò Ï ÔÓ Ô ÔÕ Ö Ø ÚÙ Û ÜÞÝ Ú ß àá ãâ Ý Ú ä ä å Ú Ö Ù æù ç è êé Ú ë Û ìè ç ç è ÚÙ ä íïî ð Ú ñ ò Ö óù ô æ ç ò å å å Û Û öõ å øù úù ù ûü þý ÿ ÿ þ ü û ý ûü ý þ ÿ ý ü û ý ÿ "! # " # $ % '& ' '( )* +,. / * ) +5 6, 8 9;: <, =? A@ <, C +5 6 D 8 9 < D = 8, < D C FE 5 G IH, IJ D J <

18 K [ XW P N UV [ XW TO P _ ] UV a f kj p sl r d d i v xy z ~ Pintrs t Functins A pintr t a functin dtrmins th prttyp f this functin, but it ds nt spcify its implmntatin: MU L N ^ M V LM U [P SZ TO S R OP U N ] N LM R LM MU L N ^ M V [P M ] N V S Z R P N LM ` ` ` u can assign an xisting functin t th pintr as lng as bth hav idntical paramtr lists and rturn typs: b h c d t p mn l gh bc ci h cq n u : {} thrugh th pintr u can call th functin ˆ ƒ ~

19 Œ ž Ÿ ž Ž Ÿ ž ««Functins as Paramtrs Œ Ž Ž Š ž ž œ Ž š Ž š Œ ž ž «ª;«Œ Ž ž ²± Ž «Ž

20 À À ¹» ¹ ½ µ ³ º ¾ º ÅÆ ¹ ½ ½Ä ¹ ¹ º º Ã Â º È ÑÐ ÙØ Functins as Paramtrs µá» ¼» ¼ ¼» ¹º Ç Æ Æ» ¼» ¼ ¼» ¼ is calld: a virtual functin; its implmntatin is nt knn t but ill b prvidd hn is calld. ÉËÊ ÒËÓ Ì}Í Ô}Õ Î Ê Ö Ó ÉËÏ ÒË a callback functin, bcaus it calls back th functin supplid by th clint.

21 ÝÜ Þ ìß é á ê æ åä ãâ ï ìß í á ñ ô ï ì ãü âý âý ù ìß é á á ê æ åä ãâ ñ ô ìß ï ìß í í á ñ ñ ìß Gnric Sarch C ds nt supprt plymrphic prgramming, but it can b ). Û Ú simulatd using gnric pintrs (i.. A functin prttyp may spcify that a blck f mmry and th valu it is lking fr ar nt typd: ðòñ æ ïî í çè á â ßà êë à êæ à ã ö õ ã ä ë êë ã ßó â ã ßó â ø í á ã å ãÿ ä åä ü ã å êÿ ì þ ã ã õ ã ä ë áûú à ê à í ø ã ß ó â ã ß ó â ðòñ æ ïî í çè á â ßà êë à êæ à ã é ö á â êë à êæ ã åä ü ÿ êæ í é ßà ãõ ä ë êë ö ö í êë á â à êæ

22 Implmntatin f Gnric Sarch (incrrct)! " " # $ &% % % ' # (

23 Implmntatin f Gnric Sarch ) * +, / * 3 40 *, ) :;, )< = +, )< ; 5 4 6) 5. 9 ;, ) < = + 9? ) < ; ) * A@ / *, ) ; 40 *, ) C 5 4 6) A D ) E : F F HG I I / + / * J D E 4 / 3 A F : D A K : L, ) < 9? ) < D A L F 9? ) < ) E 3 40 A@ /. 3 A ; 5. 9 / + / * M D / + / * J D N

24 c b [Z [Z V UT SR ` f g c b V UT SR ` [Z [Z f g Applicatin f Gnric Sarch Th clint's rspnsibilitis: ]_a X S W ]_^ X S W O P P SR P SR ] a ] ^ Pd d X O X O ]_a W ] ^ W O P Sh P SR Sh P SR b a ] X S V ] b ^ ] X S V ] Pd d Nt that this callback is sufficint fr sarch, but nt fr srt.

25 ij kml l n qp r ts s u q v t x p y q x p z j i { u t }~ sƒ n j sƒ n ˆ Š t r uœ Œ q n n s p Œ }~ j y Ž s uœ sƒ n r Œ ~ ~k u s x Œ }~ š š ij t r q n Ž j i uœ y qp t uœ œ n u ž Ÿ u x Œ r Œ ~ ~k l x t r uœ œ u q y œ y ts s u r z q n ƒ y t y q x p z t Œ }~ ž y Ž s uœ sƒ n p s l t s r

26 NAME qsrt srts an array SNOPSIS #includ <stdlib.h vid qsrt(vid *bas, siz_t nmmb, siz_t siz, int(*cmpar)(cnst vid *, cnst vid *)); DESCRIPTION Th qsrt() functin srts an array ith nmmb lmnts f siz siz. Th bas argumnt pints t th start f th array. Th cntnts f th array ar srtd in ascnding rdr accrding t a cmparisn functin pintd t by cmpar, hich is calld ith t argumnts that pint t th bjcts bing cmpard. Th cmparisn functin must rturn an intgr lss than, qual t, r gratr than zr if th first argumnt is cnsidrd t b rspctivly lss than, qual t, r gratr than th scnd. If t mmbrs cmpar as qual, thir rdr in th srtd array is undfind.

An Example file... log.txt

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