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