”;
Fortran allows you to define derived data types. A derived data type is also called a structure, and it can consist of data objects of different types.
Derived data types are used to represent a record. E.g. 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 Derived data type
To define a derived data type, the type and end type statements are used. . The type statement defines a new data type, with more than one member for your program. The format of the type statement is this −
type type_name declarations end type
Here is the way you would declare the Book structure −
type Books character(len = 50) :: title character(len = 50) :: author character(len = 150) :: subject integer :: book_id end type Books
Accessing Structure Members
An object of a derived data type is called a structure.
A structure of type Books can be created in a type declaration statement like −
type(Books) :: book1
The components of the structure can be accessed using the component selector character (%) −
book1%title = "C Programming" book1%author = "Nuha Ali" book1%subject = "C Programming Tutorial" book1%book_id = 6495407
Note that there are no spaces before and after the % symbol.
Example
The following program illustrates the above concepts −
program deriveDataType
!type declaration
type Books
character(len = 50) :: title
character(len = 50) :: author
character(len = 150) :: subject
integer :: book_id
end type Books
!declaring type variables
type(Books) :: book1
type(Books) :: book2
!accessing the components of the structure
book1%title = "C Programming"
book1%author = "Nuha Ali"
book1%subject = "C Programming Tutorial"
book1%book_id = 6495407
book2%title = "Telecom Billing"
book2%author = "Zara Ali"
book2%subject = "Telecom Billing Tutorial"
book2%book_id = 6495700
!display book info
Print *, book1%title
Print *, book1%author
Print *, book1%subject
Print *, book1%book_id
Print *, book2%title
Print *, book2%author
Print *, book2%subject
Print *, book2%book_id
end program deriveDataType
When the above code is compiled and executed, it produces the following result −
C Programming Nuha Ali C Programming Tutorial 6495407 Telecom Billing Zara Ali Telecom Billing Tutorial 6495700
Array of Structures
You can also create arrays of a derived type −
type(Books), dimension(2) :: list
Individual elements of the array could be accessed as −
list(1)%title = "C Programming" list(1)%author = "Nuha Ali" list(1)%subject = "C Programming Tutorial" list(1)%book_id = 6495407
The following program illustrates the concept −
program deriveDataType
!type declaration
type Books
character(len = 50) :: title
character(len = 50) :: author
character(len = 150) :: subject
integer :: book_id
end type Books
!declaring array of books
type(Books), dimension(2) :: list
!accessing the components of the structure
list(1)%title = "C Programming"
list(1)%author = "Nuha Ali"
list(1)%subject = "C Programming Tutorial"
list(1)%book_id = 6495407
list(2)%title = "Telecom Billing"
list(2)%author = "Zara Ali"
list(2)%subject = "Telecom Billing Tutorial"
list(2)%book_id = 6495700
!display book info
Print *, list(1)%title
Print *, list(1)%author
Print *, list(1)%subject
Print *, list(1)%book_id
Print *, list(1)%title
Print *, list(2)%author
Print *, list(2)%subject
Print *, list(2)%book_id
end program deriveDataType
When the above code is compiled and executed, it produces the following result −
C Programming Nuha Ali C Programming Tutorial 6495407 C Programming Zara Ali Telecom Billing Tutorial 6495700
”;