Computer Programming Practice (2008 Winter) Practice 10 C Scoping & Pointer

Transcription

1 Computer Programming Practice (2008 Winter) Practice 10 C Scoping & Pointer

2 2/14 Contents C Scoping Rule Declaration / Definition Single Definition Rule C Pointer & Array Stack implementation Pointer Basic Dynamic Memory Allocation

3 3/14 C Scoping - Declaration / Definition (1/2) /* sub.h */ int i; // dec /* sub.c */ #include <stdio.h> #include "sub.h int j, k; // dec int j = 1; // def /* main.c */ #include <stdio.h> #include "sub.h" main() { printf("(main) i's address : %x\n", &i); printf("i = %d\n",i); sub1(); sub2(); void sub1() { int j = 2; // def printf("(sub1) j's address : %x\n", &j); printf("j = %d\n", j); printf("(sub1) k's address : %x\n", &k); printf("k = %d\n", k); int k = 2; // def void sub2() { printf("(sub2) j's address : %x\n", &j); printf("j = %d\n",j);

4 C Scoping - Single Definition Rule (2/2) /* sub.h */ int i; // dec /* sub.c */ #include <stdio.h> #include "sub.h" int i = 7; // def int j = 1; // def /* main.c */ #include <stdio.h> #include "sub.h" int i; // dec int k = 5; // def int main() { printf("(main) i's address : %x\n", &i); printf("(main) i = %d\n", i); printf("(main) k's address : %x\n", &k); printf("(main) k = %d\n", k); sub1(); sub2(); sub3(); sub4(); sub4(); return 0; 4/14 static int k = 2; // def (static) void sub1() { printf("(sub1) i's address : %x\n", &i); printf("(sub1) i = %d\n", i); void sub2() { printf("(sub2) j's address : %x\n", &j); printf("(sub2) j = %d\n", j); void sub3() { int i = 10; // def printf("(sub3) k's address : %x\n", &k); printf("(sub3) k = %d\n", k); printf("(sub3) i's address : %x\n", &i); printf("(sub3) i = %d\n", i); void sub4() { static j = 10; // def (static) printf("(sub4) j's address : %x\n", &j); printf("(sub4) j = %d\n", j); j++;

5 5/14 Stack (1/2) Stack 한쪽끝에서만새로운항목을삽입, 삭제가능한자료구조 Last In, First Out (LIFO) 삽입과삭제는 top 에서만일어남 top F E D C B A top top top top top top

6 6/14 Stack (2/2) Stack Operatioin push pop 데이타항목을삽입하려면스택포인터를하나만큼증가시켜주고스택의 top 에데이타항목을저장한다 데이타항목을삽입하기전에새로운항목을저장할빈공간이있는지검사해야한다 데이타항목을삭제하려면스택의 top 에있는데이타항목을제거하고스택포인터를하나만큼감소시켜준다 데이타항목을삭제하기전에스택이비어있는지를검사해야한다 full (overflow) 스택이가득차있으면새로운데이터항목을삽입불가 데이터항목을삽입하기전에먼저, 스택포인터가스택의한계에도달해있는지검사해야한다 empty (underflow) 스택이비어있으면, 데이터항목삭제불가 삭제하기전에스택포인터가기저에도달해있는지를검사해야한다

7 7/14 Array 를이용한 Stack 구현 (1/3) /* stack.h */ void make_empty(void); int is_empty(void); void push(int); int pop(void); /* test_stack.c */ #include <stdio.h> #include stack.h int main() { make_empty(); return 0; /* stack.c */ #include <stdio.h> #include stack.h static int contents[100]; static int top = 0; void make_empty(void) { int is_empty(void) { static int is_full(void) { void push(int i) { int pop(void) {

8 8/14 Array 를이용한 Stack 구현 (2/3) 헤더파일 (stack.h) 에는각함수선언 (interface) 스택파일 (stack.c) 에는각함수의기능을구현 (Implementation) make_empty : 스택을비움 top = 0 으로초기화 is_empty : 스택이비었는지검사 비교연산자 == 을사용 비었으면 1 리턴, 비어있지않으면 0 리턴 is_full : 스택이다찼는지검사 push pop 다찼으면 1 리턴, 다차지않았으면 0 리턴 스택이다찼으면 (is_full 호출 ) 에러메시지를출력하고리턴 그렇지않으면아이템을 push하고, 배열 ( 스택 ) 의인덱스를증가 스택이비었으면 (is_empty 호출 ) 에러메시지를출력하고리턴 그렇지않으면배열 ( 스택 ) 의인덱스를감소시키고해당배열아이템을리턴

9 9/14 Array 를이용한 Stack 구현 (3/3) 테스트파일 (test_stack.c) 에서는 push, pop 루틴을호출하고결과를출력한다. make_empty 를이용하여배열을초기화 3, 7, 및 9 를 push 하고 pop 루틴을 2 번수행하여각각 pop 된값을출력 is_empty 루틴을수행하여그결과를출력 pop 루틴을한번더수행한후 is_empty 루틴을수행하여그결과를출력 Makefile 을작성하여컴파일한다. File 들의 Dependency 를고려

10 10/14 Pointer Basic Pointer Operators &: Address of Operator Get the address of the variable *: Indirect Operator Get the value at the address p = &var; *p = 3; -> : Member variable of Structure 996 var p

11 11/14 Dynamic Memory Allocation malloc Allocate a Specified Number of Bytes of Memory (w/ Indeterminate Initial Values) calloc Allocate (Zero-Set) Space for a Specific Number of Objects of a Specified Size realloc Change the Size of a Previous Allocated Area (w/ Indeterminate-Valued Added Area) free Deallocate the Specified Space

12 12/14 Dynamic Memory Allocation Standard Library Function Prototype #include <stdlib.h> void *malloc(size_t size); void *calloc(size_t nobj, size_t size); void *realloc(void *ptr, size_t newsize); void free(void *ptr); Example Allocation & Deallocation should match struct node *new_node; int *pa, n = 10; new_node = malloc(sizeof(struct node)); pa = calloc(n, sizeof(int)); free(new_node); free(pa);

13 Dynamic Memory Allocation Example /* mem.c */ #include <stdio.h> #include <stdlib.h> struct node { int data; struct node *next; ; int main() { struct node *a; struct node *b; struct node *c; struct node *p; a = malloc(sizeof(struct node)); b = malloc(sizeof(struct node)); c = malloc(sizeof(struct node)); b->data = 6; b->next = c; c->data = 9; c->next = NULL; p = a; while ( p!= NULL ) { printf("%d\n", p->data); p = p->next; free(a); free(b); free(c); printf("%d\n", p->data); return 0; a->data = 3; a->next = b; 13/14 a b c NULL

14 14/14 Dynamic Memory Allocation Example 앞예제는 Segmentation fault 발생 gdb 를이용해서 Error 가발생한위치를찾고, 문제점을해결