C arrays allow you to define type of variables that can hold
several data items of the same kind but structure is
another user defined data type available in C programming, which allows you to
combine data items of different kinds.
Structures are used to represent a record, Suppose you want
to keep track of your books in a library. You might want to track the following
attributes about each book:
·
Title
·
Author
·
Subject
·
Book ID
Defining a Structure
To define a structure, you must use the struct statement. The struct statement defines a new data type,
with more than one member for your program. The format of the struct statement
is this:
struct [structure tag]
{
member definition;
member definition;
...
member definition;
} [one or more structure variables];
The structure tag is optional and each member
definition is a normal variable definition, such as int i; or float f; or any
other valid variable definition. At the end of the structure's definition,
before the final semicolon, you can specify one or more structure variables but
it is optional. Here is the way you would declare the Book structure:
struct Books
{
char title[50];
char author[50];
char subject[100];
int book_id;
} book;
Accessing Structure Members
To access any member of a structure, we use the member access operator (.).
The member access operator is coded as a period between the structure variable
name and the structure member that we wish to access. You would use struct keyword to define variables of structure type. Following is
the example to explain usage of structure:
#include <stdio.h>
#include <string.h>
struct Books
{
char title[50];
char author[50];
char subject[100];
int book_id;
};
int main( )
{
struct Books
Book1; /* Declare Book1 of type
Book */
struct Books
Book2; /* Declare Book2 of type
Book */
/* book 1 specification
*/
strcpy( Book1.title,
"C Programming");
strcpy( Book1.author,
"Nuha Ali");
strcpy( Book1.subject,
"C Programming Tutorial");
Book1.book_id =
6495407;
/* book 2 specification
*/
strcpy( Book2.title,
"Telecom Billing");
strcpy( Book2.author,
"Zara Ali");
strcpy( Book2.subject,
"Telecom Billing Tutorial");
Book2.book_id =
6495700;
/* print Book1 info */
printf( "Book 1
title : %s\n", Book1.title);
printf( "Book 1
author : %s\n", Book1.author);
printf( "Book 1
subject : %s\n", Book1.subject);
printf( "Book 1
book_id : %d\n", Book1.book_id);
/* print Book2 info */
printf( "Book 2
title : %s\n", Book2.title);
printf( "Book 2
author : %s\n", Book2.author);
printf( "Book 2
subject : %s\n", Book2.subject);
printf( "Book 2
book_id : %d\n", Book2.book_id);
return 0;
}
When the above code is compiled and executed, it produces
the following result:
Book 1 title : C Programming
Book 1 author : Nuha Ali
Book 1 subject : C Programming Tutorial
Book 1 book_id : 6495407
Book 2 title : Telecom Billing
Book 2 author : Zara Ali
Book 2 subject : Telecom Billing Tutorial
Book 2 book_id : 6495700
Structures as Function Arguments
You can pass a structure as a function argument in very
similar way as you pass any other variable or pointer. You would access
structure variables in the similar way as you have accessed in the above
example:
#include <stdio.h>
#include <string.h>
struct Books
{
char title[50];
char author[50];
char subject[100];
int book_id;
};
/* function declaration */
void printBook( struct Books book );
int main( )
{
struct Books
Book1; /* Declare Book1 of type
Book */
struct Books
Book2; /* Declare Book2 of type
Book */
/* book 1 specification
*/
strcpy( Book1.title,
"C Programming");
strcpy( Book1.author,
"Nuha Ali");
strcpy( Book1.subject,
"C Programming Tutorial");
Book1.book_id =
6495407;
/* book 2 specification
*/
strcpy( Book2.title,
"Telecom Billing");
strcpy( Book2.author,
"Zara Ali");
strcpy( Book2.subject,
"Telecom Billing Tutorial");
Book2.book_id =
6495700;
/* print Book1 info */
printBook( Book1 );
/* Print Book2 info */
printBook( Book2 );
return 0;
}
void printBook( struct Books book )
{
printf( "Book
title : %s\n", book.title);
printf( "Book
author : %s\n", book.author);
printf( "Book
subject : %s\n", book.subject);
printf( "Book
book_id : %d\n", book.book_id);
}
When the above code is compiled and executed, it produces
the following result:
Book title : C Programming
Book author : Nuha Ali
Book subject : C Programming Tutorial
Book book_id : 6495407
Book title : Telecom Billing
Book author : Zara Ali
Book subject : Telecom Billing Tutorial
Book book_id : 6495700
Pointers to Structures
You can define pointers to structures in very similar way as
you define pointer to any other variable as follows:
struct Books *struct_pointer;
Now, you can store the address of a structure variable in
the above defined pointer variable. To find the address of a structure
variable, place the & operator before the structure's name as follows:
struct_pointer = &Book1;
To access the members of a structure using a pointer to that
structure, you must use the -> operator as follows:
struct_pointer->title;
Let us re-write above example using structure pointer, hope
this will be easy for you to understand the concept:
#include <stdio.h>
#include <string.h>
struct Books
{
char title[50];
char author[50];
char subject[100];
int book_id;
};
/* function declaration */
void printBook( struct Books *book );
int main( )
{
struct Books
Book1; /* Declare Book1 of type
Book */
struct Books
Book2; /* Declare Book2 of type Book */
/* book 1 specification
*/
strcpy( Book1.title,
"C Programming");
strcpy( Book1.author,
"Nuha Ali");
strcpy( Book1.subject,
"C Programming Tutorial");
Book1.book_id =
6495407;
/* book 2 specification
*/
strcpy( Book2.title,
"Telecom Billing");
strcpy( Book2.author,
"Zara Ali");
strcpy( Book2.subject,
"Telecom Billing Tutorial");
Book2.book_id =
6495700;
/* print Book1 info by
passing address of Book1 */
printBook( &Book1
);
/* print Book2 info by
passing address of Book2 */
printBook( &Book2
);
return 0;
}
void printBook( struct Books *book )
{
printf( "Book
title : %s\n", book->title);
printf( "Book
author : %s\n", book->author);
printf( "Book
subject : %s\n", book->subject);
printf( "Book
book_id : %d\n", book->book_id);
}
When the above code is compiled and executed, it produces
the following result:
Book title : C Programming
Book author : Nuha Ali
Book subject : C Programming Tutorial
Book book_id : 6495407
Book title : Telecom Billing
Book author : Zara Ali
Book subject : Telecom Billing Tutorial
Book book_id : 6495700
Bit Fields
Bit Fields allow the packing of data in a structure. This is
especially useful when memory or data storage is at a premium. Typical
examples:
·
Packing several objects into a
machine word. e.g. 1 bit flags can be compacted.
·
Reading external file formats --
non-standard file formats could be read in. E.g. 9 bit integers.
C allows us do this in a structure definition by putting
:bit length after the variable. For example:
struct packed_struct {
unsigned int f1:1;
unsigned int f2:1;
unsigned int f3:1;
unsigned int f4:1;
unsigned int type:4;
unsigned int my_int:9;
} pack;
Here, the packed_struct
contains 6 members: Four 1 bit flags f1..f3, a 4 bit type and a 9 bit my_int.
|Footer Menu |
| Introduction | Basic Syntax | Data Types | Variables | Arrays | Constants and Literals |
| Decision Making | Functions | L values and R values | Loops | Nested if statements | Nested loops |
| Nested Switch Statements | Operators | Pointers | Scope Rules |
| Strings | Storage Classes | Structures | Switch Statement |
|Footer Menu |
| Introduction | Basic Syntax | Data Types | Variables | Arrays | Constants and Literals |
| Decision Making | Functions | L values and R values | Loops | Nested if statements | Nested loops |
| Nested Switch Statements | Operators | Pointers | Scope Rules |
| Strings | Storage Classes | Structures | Switch Statement |
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