Structure Types Lecture Notes PDF

Lecture 9 Structure types 1. Concepts of structure types 2. Structures and pointers 3. Structures with functions 4. Structures and arrays 5. Bitwise structures 1. Concepts of structure types 1. A structure type (or simple structure) is a user-defined or application specific data type,...

Lecture 9 Structure types 1. Concepts of structure types 2. Structures and pointers 3. Structures with functions 4. Structures and arrays 5. Bitwise structures 1. Concepts of structure types 1. A structure type (or simple structure) is a user-defined or application specific data type, consisting of a list of data members (elements), each with its own data types. A structure type data is also called a record in applications. 2. The size of a structure type is the sum of sizes of all its members. A structure type value is stored in contiguous memory cells with its members one after another. Operations can be applied to each member. 3. A structure type is a composite data type, combining different data types. A structure type is used to construct structured hierarchical data types.  Syntax to define a structure type: struct struct_name { data_type1 v1; data_type2 v2;...... data_typek vk; }; – The data_type1, data_type2, …, data_typek, can be any data types which have been defined. – sizeof(struct struct_name) is equal to sizeof(data_type1) + sizeof(data_type2)+…+ sizeof(data_typek) – The structure definition does not allocate any memory. It defines a template that tells the compiler the types and ordering of structure members of the structure type.  Syntax to declare structure type variable: struct struct_name struct_var; This tells compiler to allocate a memory block of sizeof(struct struct_name) bytes Syntax to access structure members Use dot operator (or structure member operator). to represent each member as a variable, and be used to set/get values or get address. struct_var. v1, &struct_var.v1 struct_var.v2, & struct_var.v2 Syntax to initialize a structure variable struct struct_name struct_var = {constant1, constant2, …}; –Initializers should match their corresponding member types in the structure definition. The rest will be set as 0. Example score (4 bytes) struct student { int id; name char name; (20 bytes) float score; Id (4 bytes) }; – This defines a structure type named struct student struct student s1; – This declares a variable s1 of the struct student type. – sizeof(struct student) or sizeof(s1) is equal to sizeof(int) + sizeof(name) + sizeof(float) = 28 bytes – Compiler allocate a memory block of 28 bytes to s1, id has the lowest address, followed by name and score in the memory block. – Use s1.id, s1.name, s1.score to access members id, name and score. i.e. s1.id = 1234; strcpy(s1.name, “john”); s1.score = 88.0;  Keyword typedef is used to define a type name Rename an existing type typedef int INT; // this define a new type name INT for the int type. INT a = 10; // this is the same as int a = 10; Define new type name struct student { typedef struct student { typedef struct { int id; int id; int id; char name; char name; char name; float score; float score; float score; }; } STUDENT; } STUDENT; typedef struct student STUDENT; STUDENT s1; struct student s1; STUDENT s1; STUDENT s2; struct student s2; sizeof(STUDENT) gives 28 STUDENT s1; s1.id = 1234; strcpy(s1.name, “John”); // can not use s1.name = “John”; s1.score = 88.0 STUDENT s1 = {1234, “John“, 88.0}; // declare and initialization s1.id holds value 1234 s1.name stores string “John” s1.score holds value 88.0 STUDENT s2 = {5678, “William“}; s2.id holds value 5678 s2.name stores string “William” s2.score holds value 0 Example struct point { int x; int y; } p1; // define struct point and declare variable p1 struct point p2; // declare p2 typedef struct { int x; int y; } POINT; POINT p1, p2; What is the sizeof(POINT)? Declare and initialize POINT p1 = {320, 100}; POINT p2 = {200, 100}; Declare, set values, get values p1.x = 320; p1.y = 100; printf(“%d,%d”,p1.x, p1.y); p2.x = 300; p2.y = 300; printf(“%d,%d”,p2.x, p2.y); Structure types support assignment operations structure type variable can be assigned to another structure type variable of the same type, can be used for initialization. Example STUDENT s1 = {1234, “John“, 88.0}; STUDENT s3 = s1; // declare and initialize by value of s1 or STUDENT s3; // declare s3 = s1; // assign value s3.id has value 1234 s3.name stores string “John” s3.score has value 88.0  Nested structures A type of a structure member can be any already defined type. A previously defined structure type can be used to define members in a new structure type, called a nested structure. Nested structures enable the construction of hierarchical data types. Example typedef struct typedef struct typedef struct { char first_name; { int dd; { int id; char mid_name; int mm; NAME name; char last_name; int yy; DATE dob; } NAME; } DATE; } PERSON; PERSON p1; strcpy(p1.name.first_name , “John”); p1.dob.dd = 15; p1.dob.mm = 3; p1.dob.yy= 1990; 2. Structures and pointers A structure type pointer can be declared to hold the address of a structure type variable. Use structure pointer operator “->” to access the member of the structure. Syntax: struct struct_name { data_type1 v1; data_type2 v2; }; struct struct_name variable_name; struct struct_name *ptr = &variable_name; ptr->v1 is equivalent to variable_name. v1 typedef struct { int x; int y; } POINT p1; POINT p1; The address of p1 is &p1, The address of p1.x is &p1.x POINT *ptr; // declare POINT type pointer ptr = &p1; // assign the address of p1 to ptr Representation equivalence: ptr -> x  (*ptr).x  p1.x &(ptr->x)  &ptr->x  &p1.x  &(*ptr).x Self-referential structures A self-referential structure is a structure type that contains a pointer variable of its own type. Self-referential structure is the foundation of many other data structures such as linked lists, trees. Example struct node { // this defines type name: struct node int val; struct node *next; // this define a pointer of struct node type }; struct node has two member variables int val and struct node *next next is a pointer pointing to a struct node type variable. Example: typedef struct node { int val; struct node *next; } NODE; NODE n1, n2, *p1 = &n1; n1.val = 1; n1.next = &n2; n2.val = 2; n2.next = NULL; printf(“%d”, p1->val); // output: 1 printf(“%d”, p1->next->val); // output: 2 Access n2 from n1, this is the foundation of linked list. 3. Structures with functions Passing a structure type value to a function is the same as passing a basic type value to a function. That is, the value of the structure type variable will be copied into the function like local variables. Syntax for passing a structure variable to a function: data_type func_name(struct struct_name argument); Example void display_student(STUDENT s) { printf(“id:%d;name:%s;score:%.1f”, s.id, s.name,s.score); } STUDENT s1={1234,”Johe”,88.0}; display_student(s1); // output: id:1234;name:John;score:88.0 // whole s1 (28 bytes) is copied into function. void display(POINT p) { printf(“%d, %d”, p.x, p.y); } POINT p1={2,3}; display(p1); // output 2,3, whole p1 (8 bytes) is copied into the function  Passing structure variable reference to a function is the same passing reference of a basic type variable to a function. Syntax: data_type func_name(struct struct_name *reference); Example void inc(POINT *p) { p->x = p->x + 1; p->y = p->x + 1; } POINT p1={2,3}; inc(&p1); // the address of p1 is copied to call stack display(p1); // output: 3, 4  Structure type as function return type When a structure type is used as a return type of a function, the structure variable value is copied out from the function local scope, similar to that of returning a basic type variable. Syntax: struct struct_name function(parameter list) { struct struct_name local_variable = {0};...... return local_variable; } struct struct_name external_variable = function(argument list); Example POINT point_inc(POINT p) { p.x = p.x+1; p.y = p.y+1; return p; } POINT p1={2,3}; POINT p2 = point_inc(p1); display(p2); //display 3,4  4. Structure arrays A structure array (array of of structures) is an array, in which each element is of the same structure type. – The representations of structure arrays are the same as basic type arrays. – Arrays of structures are commonly in used to represent / store / process data records in application programs. Syntax of declaring a structure array: struct struct_name name[length]; Example STUDENT studuents; students.id = 9; strcpy(&students.name, “Peter”); Example POINT p; POINT *pt; pt = &p; pt + 1 is pointing to p (pt+1) -> x is equivalent to p.x Structure array to functions Passing a structure array to a function is the same as passing a basic type array to a function. Examples: void display_all(POINT p[], int n){ int i; for (i=0; iy);p++;} } POINT pa={2,3,4,5}; // define array of 2 POINT type display_all(pa, 2); // pass array name as reference display_all2(pa, 2); // pass array name as pointer POINT *p=pa; display_all2(p, 2); // pass POINT pointer  Structures vs Arrays 1. Both structures and arrays store data elements in contiguous memory locations. 2. All array elements are of the same data type, elements are represented by subscript index. Structure’s elements may have different data type, elements are represented by dot operator. 3. Structures support assignment, arrays do not. 4. Structure support return type, arrays do not. 5. Passing structure variable to a function copies the structure data to the function local. Passing array name to a function copies the address of array to function local. Note: If you really want to copy array data into a function through arguments, you can define a structure type wrapping the array, then pass the structure type value to the function. 5. Bitwise structures A bit field is a structure member used to store multiple logical values as a short series of bits where each of the single bits can be addressed separately. A bitwise structure is a structure containing bit fields. Example typedef struct packet { unsigned a:2; // has has 2 bits unsigned b:6; // has has 6 bits unsigned c:4; // has has 4 bits unsigned d:4; // has has 4 bits int i:16; // has 16 bits } PACKET; PACKET data; data.a = 3; data.b = 7; data.c = 9; data.d = 15; data.i = 256; printf(“%d, %d, %d, %d”, data.a, data.b, data.c, data.d); printf(“%u, %o, %x, %d”, data.a, data.b, data.c, data.d); a b c d i 11 0 00111 1001 1111 00000000100000000  Application of bit fields – A bit field is used to represent the sign of int type – A usage of bit-fields is to represent single bit flags with each flag stored in a separate bit. – Packet header. E.g., IP4 header