Structure and union in C

February 16, 2008 at 9:08 pm · Filed under 15. Structure and union in C

  • What is a Structure?
  • Structure is a method of packing the data of different types.
  • When we require using a collection of different data items of different data types in that situation we can use a structure.
  • A structure is used as a method of handling a group of related data items of different data types.

Syntax of Using Structure
structure definition:
general format:
struct tag_name
{
data type member1;
data type member2;
….
…
}

Example of Using Structure:
struct lib_books
{
char title[20];
char author[15];
int pages;
float price;
};
To holds the details of four fields namely title, author pages and price,the keyword struct declares a structure. These are the members of the structures. Each member may belong to same or different data type. The tag name can be used to define the objects that have the tag names structure. The structure we just declared is not a variable by itself but a template for the structure. We can declare the structure variables using the tag name any where in the program. For example the statement, struct lib_books book1,book2,book3; declares the book1,book2,book3 as variables of type struct lib_books each declaration has four elements of the structure lib_books. The complete structure declaration might look like this
The complete structure declaration might look like this
struct lib_books
{
char title[20];
char author[15];
int pages;
float price;
};struct lib_books, book1, book2, book3;

Get the Length of a Node List
The node list is always keeps itself up-to-date. If an element is deleted or added, in the node list or the XML document, the list is automatically updated.
The node list has a useful property called the length. The length property return the number of node in a node list.
The following code fragment get the number of <title> elements in “bookdetails.xml”:
struct lib_books { char title[20]; char author[15]; int pages; float price; }; struct lib_books, book1, book2, book3;
The following program shows the use of structure
/* Example program for using a structure*/
#include< stdio.h >
void main()
{
int id_no;
char name[20];
char address[20];
char combination[3];
int age;
}newstudent;
printf(”Enter the student information”);
printf(”Now Enter the student id_no”);
scanf(“%d”,&newstudent.id_no);
printf(“Enter the name of the student”);
scanf(“%s”,&new student.name);
printf(“Enter the address of the student”);
scanf(“%s”,&new student.address);printf(“Enter the cmbination of the student”);
scanf(“%d”,&new student.combination);printf(Enter the age of the student”);
scanf(“%d”,&new student.age);
printf(“Student information\n”);
printf(“student id_number=%d\n”,newstudent.id_no);
printf(“student name=%s\n”,newstudent.name);
printf(“student Address=%s\n”,newstudent.address);
printf(“students combination=%s\n”,newstudent.combination);
printf(“Age of student=%d\n”,newstudent.age);
}

Union:
However the members that we compose a union all share the same storage area within the computers memory where as each member within a structure is assigned its own unique storage area. Thus unions are used to observe memory. They are useful for the application involving multiple members. Where values need not be assigned to all the members at any time. Unions like structure contain members whose individual data types may differ from one another also. Like structures union can be declared using the keyword union as follows:
Last example will create a rectangle with rounded corner:
union item
{
int m;
float p;
char c;
}
code;
The notation for accessing a union member that is nested inside a structure remains the same as for the nested structure.In effect,a union creates a storage location that can be used by one of its members at a time. When a different number is assigned to a new value the new value supercedes the previous members value. Unions may be used in all the places where a structure is allowed.

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