Microsoft PowerPoint - ch07 - 포인터 pm0415

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1 함수의인수 (argument) 전달방법 C 에서함수의인수전달방법 값에의한호출 (call-by-value): 기본적인방법 포인터에의한호출 (call-by-pointer): 포인터이용 참조에의한호출 (call-by-reference): 참조 (reference) 이용 7-35

2 값에의한호출 (call-by-value) 함수호출시에변수의값을함수에복사본으로전달 복사본이전달되며, 호출하는 (calling) 함수의변수와호출된 (called) 함수의인수 (argument) 는별도의변수로관리됨 호출된함수의인수가변경되어도, 호출한함수의변수는변경없음 값에의한호출은값만을복사해요. 100 int main(void) int i = 100; 100 i int sub( int v ) 100 v... sub( i );

3 Argument passing in Call-by-Value double average(int i, int j); void main(int argc, char *argv[]) int x, y; double d; x = 3; y = 5; d = average(x, y); printf( Average: %f n, d ); double average(int i, int j) double avg; Function Call: Function average() Return Function Call: main() stack frame for average( ) - arguments: int i, int j - local variables: double avg copy copy stack frame for main( ) - arguments: int argc, char * argv[] - local variables: int x, int y, double d Memory Stack return copy avg = (i + j)/2.0; return avg; 7-37

4 포인터에의한호출 (call-by-pointer) 함수호출시에변수의주소정보 ( 포인터 ) 를함수의매개변수로전달 참조에의한호출은주소를복사합니다. 96 int main(void) int i = 100;... sub( &i ); int sub( int *p ) i p 7-38

5 Argument passing in Call-by-Pointer double average(int *pi, int *pj); void main(int argc, char *argv[]) int x, y; double d; x = 3; y = 5; d = average(&x, &y); printf( Average: %f n, d ); double average(int *pi, int *pj) double avg; Function Call: Function average() Return Function Call: main() stack frame for average( ) - arguments: int *pi, int *pj - local copy variables: of double avg return addr copy copy of stack frame for main( ) addr - arguments: int argc, char * argv[] - local variables: int x, int y, double d Memory Stack avg = (*pi + *pj)/2.0; return avg; 7-39

6 참조에의한호출 (call-by-reference) 함수호출시에변수의주소정보 ( 참조 ) 를함수의매개변수로전달 함수의호출시에 calling 함수에서의호출은 call-by-value에서와동일 호출된함수에서의 parameter에는 & 표시가데이터유형다음에표시됨 call-by-reference의경우, 호출된함수에서호출한함수의변수값을변경할수있음 예 double average(int i, int j); // call-by-value double average(int& i, int& j); // call-by-reference void main(int argc, char *argv[]) int x, y; double d;..... d = average(x, y);

7 Argument passing in Call-by-Reference void average(int i, int j, int& sum, double& avg); void main(int argc, char *argv[]) int x, y, sum; double avg; x = 3; y = 5; average(x, y, sum, avg); cout << Sum: << sum; cout <<, Average: << avg; void average(int i, int j, int& sum, double& avg) sum = i + j; avg = sum/2.0; Function Call: Function average() Return Function Call: main() 7-41 stack frame for average( ) - arguments: int i, j, int&sum, double& avg - local variables: copy ref ref stack frame for main( ) - arguments: int argc, char * argv[] - local variables: int x, y, sum, double avg Memory Stack

8 swap() 함수 #1 call-by-value 변수 2 개의값을바꾸는작업을함수로작성 #include <stdio.h> void swap(int x, int y); int main(void) int a = 100, b = 200; printf("a=%d b=%d\n",a, b); swap(a, b); printf("a=%d b=%d\n",a, b); return 0; 100 a <main> b 함수호출시에값만복사된다. x y <swap> 7-42 void swap(int x, int y) int tmp; printf("x=%d y=%d\n",x, y); tmp = x; x = y; y = tmp; printf("x=%d y=%d\n",x, y); a=100 b=200 x=100 y=200 x=200 y=100 a=100 b=200

9 swap() 함수 #2 - call-by-pointer 포인터를이용 #include <stdio.h> void swap(int x, int y); int main(void) int a = 100, b = 200; printf("a=%d b=%d\n",a, b); swap(&a, &b); printf("a=%d b=%d\n",a, b); return 0; 함수호출시에주소가복사된다. void swap(int *px, int *py) int tmp; printf("*px=%d *py=%d\n", *px, *py); tmp = *px; *px = *py; *py = tmp; printf("*px=%d *py=%d\n", *px, *py); &a a &b b <main> px py <swap> 7-43 a=100 b=200 *px=100 *py=200 *px=200 *py=100 a=200 b=100

10 swap() 함수 #3 - call-by-reference 포인터를이용 #include <stdio.h> void swap(int& x, int& y); int main(void) int a = 100, b = 200; printf("a=%d b=%d n",a, b); swap(a, b); printf("a=%d b=%d n",a, b); return 0; 함수호출시에주소정보가전달된다. void swap(int & x, int &y) int tmp; printf("x=%d y=%d n", x, y); tmp = x; x = y; y = tmp; printf("x=%d y=%d n", x, y); a b <main> x y <swap> 7-44 a=100 b=200 x=100 y=200 x=200 y=100 a=200 b=100

11 파라메터전달방식의비교 /* TestParameterPassing.c */ #include <stdio.h> void swap_call_by_value (int x, int y); void swap_call_by_pointer(int *px, int *py); void swap_call_by_reference(int &x, int &y); void main() int x, y; x = 10; y = 30; printf(" nbefore call-by-value: x = %d, y = %d n", x, y); swap_call_by_value(x, y); printf("after call-by-value: x = %d, y = %d n", x, y); x = 5; y = 7; printf(" nbefore call-by-pointer: x = %d, y = %d n", x, y); swap_call_by_pointer(&x, &y); printf("after call-by-pointer: x = %d, y = %d n", x, y); x = 25; y = 50; printf(" nbefore call-by-reference: x = %d, y = %d n", x, y); swap_call_by_reference(x, y); printf("after call-by-reference: x = %d, y = %d n", x, y); printf(" n"); void swap_call_by_value(int a, int b) int temp; temp = a; a = b; b = temp; void swap_call_by_pointer(int *pa, int *pb) int temp; temp = *pa; *pa = *pb; *pb = temp; void swap_call_by_reference(int &a, int &b) int temp; temp = a; a = b; b = temp; 7-45

12 scanf() 함수 변수에값을저장하기위하여변수의주소를받는다. 7-46

13 2 개이상의결과를반환 #include <stdio.h> // 기울기와 y절편을계산 int get_line_parameter(int x1, int y1, int x2, int y2, float *slope, float *yintercept) if( x1 == x2 ) 기울기와 Y절편을인수로전달 return -1; else *slope = (float)(y2 - y1)/(float)(x2 - x1); *yintercept = y1 - (*slope)*x1; return 0; int main(void) float s, y; if( get_line_parameter(3,3,6,6,&s,&y) == -1 ) printf(" 에러 n"); 기울기는 , y절편은 else printf(" 기울기는 %f, y절편은 %f n", s, y); return 0; 7-47

14 일반변수 vs 배열 배열이함수인수인경우 // 매개변수 x에기억장소가할당 void sub(int x)... // b[] 에기억장소가할당되지않는다. void sub(int b[], int n)... 배열의경우, 크기가큰경우에복사하려면많은시간소모 배열의경우, 배열의주소를전달 7-48

15 예제 #include <stdio.h> void sub(int b[], int n); int main(void) int a[3] = 1,2,3 ; a[0] a[1] a[2] printf("%d %d %d\n", a[0], a[1], a[2]); sub(a, 3); printf("%d %d %d\n", a[0], a[1], a[2]); return 0; void sub(int b[], int n) b[0] = 4; b[1] = 5; b[2] = 6;

16 포인터를반환할때주의점 함수가종료되더라도남아있는변수의주소를반환하여야한다. 지역변수의주소를반환하면, 함수가종료되면사라지기때문에오류 int *add(int x, int y) int result; result = x + y; return &result; 지역변수 result 는함수가종료되면소멸되므로그주소를반환하면안된다! 7-50

17 이중포인터 (double pointer) 이중포인터 (double pointer) : 포인터를가리키는포인터 int i = 10; int *p = &i; int **q = &p; // i 는 int 형변수 // p 는 i 를가리키는포인터 // q 는포인터 p 를가리키는이중포인터 7-51

18 이중포인터 이중포인터의해석 7-52

19 이중포인터 // 이중포인터프로그램 #include <stdio.h> *q int main(void) int i = 100; int *p = &i; int **q = &p; **q p 포인터 *p = 200; printf("i=%d *p=%d **q=%d n", i, *p, **q); i 변수 i q 이중포인터 **q = 300; printf("i=%d *p=%d **q=%d n", i, *p, **q); return 0; **q == *(*q) i=200 *p=200 **q=200 i=300 *p=300 result **q=

20 예제 #2 #include <stdio.h> void set_pointer(char **q); char *proverb="all that glisters is not gold."; "All that glisters is not gold." int main(void) char *p="zzz"; set_pointer(&p); printf("%s \n", p); return 0; p *q q void set_pointer(char **q) *q = proverb; All that glisters is not gold. result 7-54

21 포인터배열 (array of pointers) 포인터배열 (array of pointers): 포인터를모아서배열로만든것 7-55

22 정수형포인터배열 int a = 10, b = 20, c = 30, d = 40, e = 50; int *pa[5] = &a, &b, &c, &d, &e ; 7-56

23 2 차원배열에문자열을저장 char fruits[4 ][10] = "apple", "blueberry", "orange", melon" ; a p p l e \0 b l u e b e r r y \0 2 차원배열을사용하면낭비되는공간이생성되죠. o r a n g e \0 낭비되는공간! m e l o n \0 7-57

24 문자형포인터배열 char *fruits[ ] = "apple", "blueberry", "orange", melon" ; a p p l e \0 fruits[0] fruits[1] fruits[2] fruits[3] b l u e b e r r y \0 o r a n g e \0 m e l o n \0 7-58

25 예제 // 문자열배열 #include <stdio.h> 각각의문자열의길이가달라도메모리의낭비가발생하지않는다. int main(void) int i, n; char *fruits[ ] = "apple", "blueberry", "orange", "melon" ; fruits[0] fruits[1] fruits[2] fruits[3] a p p l e \0 b l u e b e o r a n g m e l o n \0 r e \0 r y \0 // 배열원소개수계산 n = sizeof(fruits)/sizeof(fruits[0]); for(i = 0; i < n; i++) printf("%s \n", fruits[i]); apple result blueberry orange melon return 0; 7-59

26 배열포인터 배열포인터 (a pointer to an array) 는배열을가리키는포인터 7-60

27 예제 #include <stdio.h> int main(void) int a[5] = 1, 2, 3, 4, 5 ; int (*pa)[5]; int i; pa = &a; for(i=0 ; i<5 ; i++) printf("%d n", (*pa)[i]); return 0; result 7-61

28 다차원배열과포인터 2차원배열 int m[3][3] 1행->2행->3행->... 순으로메모리에저장 ( 행우선방법 ) 하나의열 m m[0][0] m[0][0] m[0][1] m[0][1] 1 행 m[0] 하나의행 m[0][2] m[0][2] m[1][0] m[1][0] m[1] m[0][0] m[0][0] m[0][1] m[0][1] m[0][2] m[0][2] m[1][1] m[1][1] 2 행 열 (column) m[1][0] m[1][0] 행m[2][0] m[2][0] (row) m[1][1] m[1][1] m[2][1] m[2][1] m[1][2] m[1][2] m[2][2] m[2][2] m[1][2] m[1][2] m[2][0] m[2][0] m[2] m[2][1] m[2][1] 3 행 7-62 m[2][2] m[2][2]

29 배열이름 m은 &m[0][0] m[0] 는 1행의시작주소 m[1] 은 2행의시작주소... 2 차원배열과포인터 m m[0] m[0] m[0][0] m[0][0] m[0][1] m[0][1] m[0][2] m[0][2] m[1] m[1] m[1][0] m[1][0] m[1][1] m[1][1] m[1][2] m[1][2] m[2] m[2] m[2][0] m[2][0] m[2][1] m[2][1] m[2][2] m[2][2] 7-63

30 2 차원배열의해석 m 은세개의원소를가지는배열이다. int m[3][3]; 해석의방향 그원소들은다시세개의원소로되어있다. 7-64

31 multi_array.c // 다차원배열과포인터 #include <stdio.h> int main(void) int m[3][3] = 10, 20, 30, 40, 50, 60, 70, 80, 9 0 ; printf("m = %p\n", m); printf("m[0] = %p\n", m[0]); printf("m[1] = %p\n", m[1]); printf("m[2] = %p\n", m[2]); printf("&m[0][0] = %p\n", &m[0][0]); printf("&m[1][0] = %p\n", &m[1][0]); printf("&m[2][0] = %p\n", &m[2][0]); return 0; m m[0] m[1] m[2] m = m[0] = m[1] = m[2] = &m[0][0] = &m[1][0] = &m[2][0] = m[0][0] m[0][1] m[0][2] m[1][0] m[1][1] m[1][2] m[2][0] m[2][1] m[2][2] result 7-65

32 Multidimensional Dynamic Arrays 2-dimensional Dynamic Array of double type (1) double DA[ROWS][COLS]; ppda step-2: one-dimensional array of COLS double elements this element can be accessed as ppda[0][0] step-1: one-dimensional array of ROWS pointers to 4 rows (4 one-dimensional array) this element can be accessed as ppda[3][2] can be considered as four rows of one dimensional array: DA[i][0..4] each row is pointed by a pointer to 1-dimension array: Array of pointers to the four 1-dimension arrays of pointers double **ppda = (double **)malloc(sizeof(double *) * ROWS); To make the 2-dimensional array ppda[i] = (double *)malloc(sizeof(double) * COLS); 7-66

33 Multidimensional Dynamic Arrays Multi-dimensional array is "arrays of arrays" Type definitions help "see it": #define NUM_ROWS 3 #define NUM_COLS 4 int **ma; ma = (int **)malloc(sizeof(int *) * NUM_ROWS); // Creates array of three pointers // We can make each m[i] to point an dynamically allocated array of 4 integers for (int i = 0; i < NUM_ROWS; i++) ma[i] = (int *)malloc(sizeof(int) * NUM_COLS); // Results in 3 x 4 dynamic array! 7-67

34 2-dimensional Dynamic Array of double type (2) double **ppda = (double **)malloc (sizeof(double*) * NUM_ROW); for (int i=0; i<num_row; i++) ppda[i] = (double *) malloc (sizeof(double) * NUM_COLUMN); ppda[2][3] = 1.0; typedef double* DblPtr DblPtr *ppdb = (DblPtr *)malloc(sizeof(dblptr) * NUM_ROW); for (int i=0; i<num_row; i++) ppdb[i] = (DblPtr) malloc (sizeof (double) * NUM_COLUMN); ppdb[2][3] = 1.0; 7-68

35 2 차원배열과포인터연산 2 차원배열 m[][] 에서 m 에 1 을더하거나빼면어떤의미일까? 7-69

36 포인터를이용한배열원소방문 행의평균을구하는경우 double get_row_avg(int m[][cols], int r) int *p, *endp; double sum = 0.0; m[0][0] m[0][0] m[0][1] m[0][1 ] m[0][2] m[0][2] p = &m[r][0]; endp = &m[r][cols]; while( p < endp ) sum += *p++; 열 (column) m[1][0] m[1 ][0] 행m[2][0] m[2][0] (row) m[3][0] m[3][0] m[1][1] m[1 ][1 ] m[2][1] m[2][1 ] m[3][1] m[3][1 ] m[1][2] m[1][2] m[2][2] m[2][2] m[3][2] m[3][2] sum /= COLS; return sum; p endp endp 7-70

37 포인터를이용한배열원소방문 전체원소의평균을구하는경우 double get_total_avg(int m[][cols]) int *p, *endp; double sum = 0.0; m[0][0] m[0][0] m[0][1 m[0][1 ] ] m[0][2] m[0][2] p = &m[0][0]; endp = &m[rows-1][cols]; m[1][0] m[1][0] m[1][1 m[1 ][1 ] ] m[1][2] m[1][2] while( p < endp ) sum += *p++; sum /= ROWS * COLS; return sum; p m[2][0] m[2][0] m[3][0] m[3][0] m[2][1 m[2][1 ] ] m[3][1] m[3][1] 열 (column) 행(row) m[2][2] m[2][2] m[3][2] m[3][2] endp endp 7-71

38 const 포인터 const 를붙이는위치에따라서의미가달라진다. p 가가리키는내용이변경되지않음을나타낸다. 포인터 p 가변경되지않음을나타낸다. const char *p; char * const p; 7-72

39 예제 #include <stdio.h> int main(void) char s[] = "Barking dogs seldom bite."; char t[] = "A bad workman blames his tools"; const char * p=s; char * const q=s; //p[3] = 'a'; p 가가리키는곳의내용을변경할수없다. p = t; q[3] = 'a ; 하지만 p 는변경이가능하다. q 가가리키는곳의내용은변경할수있다. //q = t; 하지만 q 는변경이불가능하다. return 0; 7-73

40 main() 함수의인수 지금까지의 main() 함수형태 int main(void).. 외부로부터입력을받는 main() 함수형태 int main(int argc, char *argv[])

41 인수전달방법 C: \cprogram> mycopy src dst m y c c o o p y \0 \0 argv[0] s s r r c c \0 \0 argv[1] d s s t t \0 \0 3 3 argv[2] argc argv 배열 7-75

42 비주얼 C++ 프로그램인수입력방법 Project -> <YourProjectName> Properties -> Configuration Properties -> Debugging -> Command Arguments (Visual Studio 2015) 7-76

43 /* Power.cpp */ power.c #include <stdio.h> #include <stdlib.h> int main(int argc, char *argv[]) char mode; if (argc < 4) printf("usage: >power r (or i) base exponent"); exit(-1); printf("argc: %d n", argc); for (int i = 0; i < argc; i++) printf("argv[%d] : %s n", i, argv[i]); if (*argv[1] == 'r') printf("power(base, exponent) calculation with recursive mode n"); else if (*argv[1] == 'i') printf("power(base, exponent) calculation with recursive mode n"); 7-77

44 main 함수로 arguments 전달프로그램실행예제 (1) 7-78

45 main 함수로 arguments 전달프로그램실행예제 (2) 7-79