Contents. Custom data type struct data type Fixed length memory Alias data type

Transcription

1 Complex Data Type

2 Contents Custom data type struct data type Fixed length memory Alias data type

3 Custom data type

4 Terminology primitive data type the data type that don't need to be defined; they are already known by C language. int, float, double, char and pointer custom data type the data type that be defined. come from library or user-defined. predefined data type the custom data type that be defined with in C standard header. FILE, size_t and etc.

5 Custom data type we can define data type in several way include structure data type the data type that is the combination of other data type ( include another custom data type) struct is non-overlapped memory space structure data type union is overlapped memory space structure data type alias data type the data type that don't define anything except its name. it is alias name of other data type.

6 Custom data type using usually, we can use custom data type in the same way that we can do with primitive data type; except: we cannot use arithmetic operations with structure data type or other data type that be defined from it. that means we can: create array of custom data type create pointer of custom data type pass custom data type as argument to function return custom data type from function and so on

7 struct data type

8 struct definition phrase syntax struct [tag_name]{ data-type member_name; data-type another_member_name;... } tag_name can be ignored when use with variable declaration or typedef definition otherwise we can't refer to defined struct variables were declared with in struct are called members

9 struct definition (cont.) example define for use later (; is necessary) struct st01{ long int a; char b; }; single use with variable declaration (tag_name isn't necessary) struct{ long int a; char b; } st_var; // st_var is a variable

10 struct definition (cont.) example (cont.) self reference (tag_name is necessary) struct linked_node{ long int value; struct linked_node *next; }; // self reference must define in pointer term // unless it can't determine the memory size

11 accessing struct member we can access member of struct in variable by using. operator and treat it as normal variable. struct st01{ long int a; char b; }; struct st01 x; x.a = 123; x.b = 'c'; printf("%d, %c\n", x.a, x.b); printf("address of x.b = %p\n", &x.b);

12 Memory allocation of struct consider following code struct st01{ long int a; char b; }; struct st01 x; x.a = 1; x.b = 'c';

13 Memory allocation of struct (cont.) the allocated memory for x variable shown below assume x variable got memory address at 0xAB10 x refer to -> 0xAB10 0xAB11 0xAB12 0xAB13 0xAB14 0xAB15 0xAB16 1 c size of long int (a) size of char (b) size of struct st01 (x)

14 Basics of struct Let us create a few structures suitable for graphics. The basic object is a point, which we will assume has an x coordinate and a y coordinate, both integers.

15 Basics of struct (cont.) The two components can be placed in a structure declared like this: struct point{ int x; int y; }; Now we can declare pt variable with struct point data type struct point pt; pt.x = 4; pt.y = 3; or we can declare and initial it (will be explained later in the end of this section) struct point pt = {4, 3};

16 Basics of struct (cont.) To compute the distance from the origin (0,0) to pt double dist; dist = sqrt( (double)pt.x * pt.x + (double)pt.y * pt.y );

17 Basics of struct (cont.) For now we will create rectangular object that contain two point

18 Basics of struct (cont.) We define rectangular structure with the following struct struct rect { struct point pt1; struct point pt2; }; And we declare screen variable and assign pt1 and pt2 member struct rect screen; struct point start_pt = {4, 3} struct point end_pt = {6, 5}; screen.pt1 = start_pt; screen.pt2 = end_pt;

19 Basics of struct (cont.) Or we can assign x and y directly to screen variable screen.pt1.x = 4; screen.pt1.y = 3; screen.pt2.x = 6; screen.pt2.y = 5; We can't assign struct value in the way of initialization screen.pt1 = {4, 3}; // Syntax error!!! Both previous assignment is verbose code; in the next content will use function to make this process easer.

20 Structures and Functions The first function, makepoint, will take two integers and return a struct point /* makepoint: make a point from x and y components */ struct point makepoint(int x, int y){ struct point temp; temp.x = x; temp.y = y; return temp; }

21 Structures and Functions (cont.) makepoint can now be used to initialize any structure dynamically, or to provide structure arguments to a function: struct rect screen; struct point middle; // middle point of screen screen.pt1 = makepoint(4,3); screen.pt2 = makepoint(6, 5); middle = makepoint((screen.pt1.x + screen.pt2.x)/2, (screen.pt1.y + screen.pt2.y)/2); printf("middle point of (%d, %d), (%d, %d) = (%d, %d)\n", screen.pt1.x, screen.pt1.y, screen.pt2.x, screen.pt2.y, middle.x, middle.y); // middle point of (4, 3), (6, 5) = (5, 4)

22 Structures and Functions (cont.) As another example, the function ptinrect tests whether a point is inside a rectangle, where we have adopted the convention that a rectangle includes its left and bottom sides but not its top and right sides: /* ptinrect: return 1 if p in r, 0 if not */ /* r.pt1 is left-bottom and r.pt2 is right-top */ int ptinrect(struct point p, struct rect r){ return p.x >= r.pt1.x && p.x < r.pt2.x && p.y >= r.pt1.y && p.y < r.pt2.y; }

23 Structures and Functions (cont.) Now we use ptinrect by following code: struct point pt = makepoint(5, 3); printf("(%d, %d) is%s in (%d, %d), (%d,%d)\n", pt.x, pt.y, (ptinrect(pt, screen))? "" : " not", screen.pt1.x, screen.pt1.y, screen.pt2.x, screen.pt2.y); // (5, 3) is in (4, 3), (6,5)

24 Full Example #include <stdio.h> struct point{ int x; int y; }; struct rect{ struct point pt1; struct point pt2; }; //next

25 Full Example (cont.) struct point makepoint(int x, int y); int ptinrect(struct point p, struct rect r); int main(int argc, char *argv[]){ struct rect screen; struct point middle; // middle point of screen // next

26 Full Example (cont.) screen.pt1 = makepoint(4, 3); screen.pt2 = makepoint(6, 5); middle = makepoint((screen.pt1.x + screen.pt2.x)/2, (screen.pt1.y + screen.pt2.y)/2); printf("middle point of (%d, %d), (%d, %d) = (%d, %d)\n", screen.pt1.x, screen.pt1.y, screen.pt2.x, screen.pt2.y, middle.x, middle.y); // next

27 Full Example (cont.) struct point pt = makepoint(5, 3); printf("(%d, %d) is%s in (%d, %d), (%d,%d)\n", pt.x, pt.y, (ptinrect(pt, screen))? "" : " not", screen.pt1.x, screen.pt1.y, screen.pt2.x, screen.pt2.y); } // next return 0;

28 Full Example (cont.) /* makepoint: make a point from x and y components */ struct point makepoint(int x, int y){ struct point temp; temp.x = x; temp.y = y; return temp; } // next

29 Full Example (cont.) /* ptinrect: return 1 if p in r, 0 if not */ /* r.pt1 must be left-bottom and r.pt2 must be right-top */ int ptinrect(struct point p, struct rect r){ return p.x >= r.pt1.x && p.x < r.pt2.x && p.y >= r.pt1.y && p.y < r.pt2.y; }

30 struct initialization struct initialization aka automatic structure we can initial struct in the same way that initial array by using braces and assign value to specific data type struct st01{ long int a; char b; } struct st01 x = {1, 'c'};

31 struct initialization for nested struct sush as stuct rect in the previous example we can use nested braces to assign that value struct rect screen = { {4, 3}, {6, 5} }; the braces just assign value that span memory length so nested braces may be ignore (but cause a warning on compile time) struct rect screen = {4, 3, 5, 6};

32 struct initialization (cont.) Indeed, braces initialization do the same task on both struct and array it assigns given value to span memory length so initialization of 2-dimensional array or multi-dimensional array can ignore nested braces too int ar1[3][2] = {1, 2, 3, 4, 5, 6}; // same as int ar2[3][2] = {{1, 2}, {3, 4}, {5, 6}}; // same as int ar3[][2] = {1, 2, 3, 4, 5, 6}; // this is automatic array // the leftmost dimension size be calculated automatically

33 Notable struct and array have some same advantage they can contain multiple value. but they have some deference too. struct can contain multiple data type, but array can contain just single data type. we can loop through array elements but we can't do that with struct members and keep in your mind struct is data type. array is not data type, it is type of variable.

34 Notable (cont.) bit length in struct definition, we can specific member size in unit of bit by suffix member_name with : number_of_bit struct flags{ unsigned int is_keyword : 1; unsigned int is_extern : 1; unsigned int is_static : 1; }; // used memory is 3 bit of unsinged int // so total allocated memory = sizeof (unsigned int) it often used in system programming or hardware programming but rarely used in application programming.

35 Notable (cont.) for gcc (C compiler that used in this course), we can cast braces constant to assign struct value; but it isn't part of ANSI-C standard (don't use it) screen.pt1 = (struct point){4, 3};

36 Fixed length memory

37 Fixed length memory struct is fixed length memory it uses equal memory length for all variable that have it as data type. stuct st{ long int a; double b; } // used memory = sizeof (long int) + sizeof (double) // = = 12 bytes this behavior is same as primitive data type such as int, char, double and etc. so we can assign struct value by struct st x = {1, 2.1}; struct st y; y = x; // this expression is OK and copy value from x to y

38 Fixed length memory (cont.) we know long that we can't copy array by using = operator long int ar1[4] = {1, 2, 3, 4}; long int ar2[4]; ar2 = ar1; // ERROR: assignment to expression with array type but for struct struct st{ long int ar[4]; } // used memory = 4 * sizeof (long int) = 4 * 4 = 16 bytes struct st x = {{1, 2, 3, 4}}; struct st y; y = x; // this expression works!!! it copy x.ar to y.ar WHY??? just put array in struct and we can copy it.

39 Fixed length memory (cont.) fixed length memory come to handle this, C handle = operator for struct by following process. because it is fixed length memory it guarantees two variable have equal memory length. and each member have the same data type. it will copy memory value byte-by-byte to another; similarly to following code memcpy(&y, &x, sizeof (struct st)); will explain memcpy later in the chapter of dynamic memory allocation that why we can copy array in struct

40 Fixed length memory (cont.) Indeed, we can copy array in the way of C handle struct memcpy(ar2, ar1, 4 * sizeof (long int)); in the previous example case, we know exactly ar1 and ar2 have equal memory length and same data type. but in the other case, it doesn't guarantee that both variables have equal memory length and same data type, so you may got junk data in ar2 variable.

41 Fixed length memory (cont.) In conclusion, because of fixed length memory, we can treat stuct as primitive data type such as: pass them by value to function; unlike array that must be passed by reference return them from function and assign (copy value) them to another variable and so on

42 Alias data type

43 typedef definition syntax typedef existed_data_type alias_name; It must be emphasized that a typedef definition does not create a new data type in any sense; it merely adds a new name for some existing data type

44 typedef definition (cont.) example typedef char int8; typedef short int int16; typedef long int int32; typedef long long int int64; printf("%d, %d, %d, %d\n", (int)sizeof (int8), (int)sizeof (int16), (int)sizeof (int32), (int)sizeof (int64)); // 1, 2, 4, 8

45 typedef definition (cont.) example typedef for struct typedef struct st01{ long int a; char b; } type_st01; // define type_st01 as struct st01 type_st01 x = {1, 'c'};

46 typedef definition (cont.) example typedef name same as tag_name typedef struct st01{ long int a; char b; } st01; // define st01 as struct st01 // we can define typedef name same as struct tag_name st01 x = {1, 'c'}; // with out struct keyword

47 typedef definition (cont.) example typedef for anonymous struct typedef struct{ long int a; char b; } st01; // define st01 as anonymous struct st01 x = {1, 'c'}; // with out struct keyword

48 typedef definition (cont.) example typedef for struct that have self reference must specific tag_name typedef struct linked_node{ long int value; struct linked_node *next; // must use struct } linked_node; // define linked_node as struct linked_node liked_node x; // with out struct keyword

49 References Brian W., Dennis M., C Programming Language: second edition.