Structures (1A) Young Won Lim 12/4/17

Transcription

1 Structures (1A)

2 Copyright (c) Young W. Lim. Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.2 or any later version published by the Free Software Foundation; with no Invariant Sections, no Front-Cover Texts, and no Back-Cover Texts. A copy of the license is included in the section entitled "GNU Free Documentation License". Please send corrections (or suggestions) to youngwlim@hotmail.com. This document was produced by using LibreOffice.

3 Structure Variable Declaration accessing a structure variable definition &var var struct aaa var; var declaration &var = &var.i &var.s &var.c var.i var.s var.c accessing its members 3

4 Compare with function definitions function type int add (int x, int y) ; prototype definition int add (int x, int y) { return (x + y); } definition struct aaa var; var declaration var.i = 100; member access sum = add (30, 20) ; function call 4

5 Struct Variable Declaration (1) definition } var ; struct aaa var; var declaration 5

6 Struct Variable Declaration (2) definition } var ; struct aaa var; var declaration definition + variable declaration 6

7 Struct Variable Declaration (3) typedef } ATYPE ; typedef struct aaa ATYPE ; ATYPE var; ATYPE var; 7

8 Struct Variable Declaration (4) typedef } ATYPE ; typedef struct aaa ATYPE ; ATYPE var; ATYPE var; 8

9 Struct Variable Declaration Summary struct aaa var; typedef struct aaa ATYPE ; ATYPE var; } var ; typedef } ATYPE ; ATYPE var; 9

10 Initialization &v1.s &v1.i &v1.c v1.s v1.i v1.c =100 =10 = A &v2.s &v2.i &v2.c v2.s v2.i v2.c struct aaa v1 = { 100, 10, 'A' struct aaa v2; 10

11 Assignments &v1.s &v1.i &v1.c v1.s v1.i v1.c =100 =10 = A &v2.s &v2.i &v2.c v2.s v2.i v2.c v2 = v1 ; v1 v2 v2.i = v1.i ; v2.s = v1.s ; v2.c = v1.c ; v1.s v1.i v1.c =100 =10 = A v2.s v2.i v2.c =100 =10 = A 11

12 Variable Declaration Allocates Memory definition struct aaa v1 = { 100, 10, 'A' &v1 v1.s =100 v1.i =10 v1.c = A 12

13 Pointer to Structure Variable Declaration p struct aaa *p ; &v1 v1.s =100 v1.i =10 v1.c = A pointer variable assignment p p = &v1; &v1 p->s p->i p->c 13

14 Dereferencing Pointers to Structures (1) (*p).mem p->mem &var var &var = &var.i var.i &var.s var.s &var.c var.c p p (*p) (*p)->s (*p)->i (*p)->c = p->s = p->i = p->c = v1.s = v1.i = v1.c 14

15 Dereferencing Pointers to Structures (2) *p.mem *(p.mem) p : a struct variable mem : another pointer variable &p p &p = &p.i p.i &p.s p.s &p.q p.q *p.q 15

16 Dereferencing Pointers to Structures (3) *p->mem *(p->mem) p : a pointer to a struct variable mem: another pointer variable p p (*p) (*p)->s (*p)->i (*p)->q = p->s = p->i = p->q = v1.s = v1.i = v1.q *p->q 16

17 Dereferencing Pointers to Structures definition (*p).mem p->mem struct aaa v1 = { 100, 10, 'A' *p.mem *(p.mem) struct aaa *p = &v1; *p->mem *(p->mem) 17

18 Memory Layout (1) definition sizeof (int) = 4 bytes sizeof (short) = 2 bytes sizeof (char) = 1 bytes &var.i (int) var.i struct aaa var; var declaration &var.s (short) var.s address data &var.c (char) var.i &var.i &var.s &var.c var.i var.s var.c sizeof (var) = 8 bytes 18

19 Memory Layout (2) definition &var.s (short) var.s struct aaa var; var declaration &var.i (int) var.i address data &var.c (char) var.i &var.s &var.i &var.c var.s var.i var.c sizeof (var) = 12 bytes 19

20 Struct Definition and Declarations definition 8 bits var 8 bits struct aaa var; var declaration var.i var.c struct aaa *ptr; var declaration ptr 20

21 Nested Structures struct point { int x ; int y ; struct rect { struct point p1 ; struct point p2 ; address data &r.p1 r.p1 &r.p2 r.p2 struct point pa ; struct rect r ; struct point pb ; &r.p1.x r.p1.x &r.p1.y r.p1.y pa.x = 10 ; pa.y = 20 ; pb.x = 300 ; pb.y = 400 ; r.p1 = pa ; r.p2 = pb ; &r.p2.x &r.p2.y r.p2.x r.p2.y 21

22 Array Implementation // within main() int i ; char * name[3] = { John, Mary, Baker }; int stid[3] = { , , }; int eng[3] = { 94, 85, 90 }; int math[3] = { 88, 92, 98 }; double gpa[3]; for (i=0; i<3; ++i) printf( \n ); printf( name: %s \n, name[i] ); printf( stid: %d \n, stid[i] ); printf( eng: %d \n, eng[i] ); printf( math: %d \n, math[i] ); printf( gpa: %f \n, (eng[i] + math[i]) / 2. ); } 22

23 Struct Implementation // outside main() struct srec { char * name ; int stid ; int eng ; int math ; double gpa ; // within main() struct srec S[3] = { { John, , 94, 88 }, { Mary, , 85, 92 }, { Baker, , 90, 98 } }; for (i=0; i<3; ++i) printf( \n ); printf( name: %s \n, S[i].name ); printf( stid: %d \n, S[i].stid ); printf( eng: %d \n, S[i].eng ); printf( math: %d \n, S[i].math ); printf( gpa: %f \n, (S[i].eng + S[i].math) / 2. ); } 23

24 Struct as a function argument // outside main() struct srec { char * name ; int stid ; int eng ; int math ; double gpa ; double compute_gpa (struct srec R) { return (R.eng + R.math) / 2. ; } // within main() struct srec S = { John, , 94, 88 }; gpa = compute_gpa ( S ); double compute_gpa (struct srec R) gpa = compute_gpa ( S ); S.name, S.stid, S.eng, S.math, S.gpa char *, int, int, int, double R.name, R.stid, R.eng, R.math, R.gpa double compute_gpa (struct srec R) double gpa; gpa = compute_gpa ( S ); 24

25 Struct returning function // outside main() struct srec { char * name ; int stid ; int eng ; int math ; double gpa ; struct srec calc_gpa (struct srec R) { R.gpa = (R.eng + R.math) / 2. ; return R; } // within main() struct srec S = { John, , 94, 88 }; gpa = calc_gpa ( S ); struct srec calc_gpa (struct srec R) S = calc_gpa ( S ); S.name, S.stid, S.eng, S.math, S.gpa char *, int, int, int, double R.name, R.stid, R.eng, R.math, R.gpa struct srec calc_gpa (struct srec R) double gpa; S = calc_gpa ( S ); 25

26 Struct pointer as a function argument // outside main() struct srec { char * name ; int stid ; int eng ; int math ; double gpa ; void fill_gpa (struct srec * R) { (*R).gpa = ((*R).eng + (*R).math) / 2. ; } // within main() struct srec S = { John, , 94, 88 }; &S R gpa = fill_gpa ( &S ); void fill_gpa (struct srec * R) ; S.name, S.stid, S.eng, S.math, S.gpa gpa = fill_gpa ( &S ); void fill_gpa (struct srec * R) ; double gpa; gpa = fill_gpa ( &S ); (*R).eng (*R).math (*R).gpa R->eng R->math R->gpa 26

27 References [1] Essential C, Nick Parlante [2] Efficient C Programming, Mark A. Weiss [3] C A Reference Manual, Samuel P. Harbison & Guy L. Steele Jr. [4] C Language Express, I. K. Chun 27