6.1.20 STRUCTURE and RECORD

Record structures are a pre-Fortran-90 vendor extension to create user-defined aggregate data types. GNU Fortran does not support record structures, only Fortran 90's “derived types”, which have a different syntax.

In many cases, record structures can easily be converted to derived types. To convert, replace STRUCTURE /structure-name/ by TYPE type-name. Additionally, replace RECORD /structure-name/ by TYPE(type-name). Finally, in the component access, replace the period (.) by the percent sign (%).

Here is an example of code using the non portable record structure syntax:

     ! Declaring a structure named ``item'' and containing three fields:
     ! an integer ID, an description string and a floating-point price.
     STRUCTURE /item/
       INTEGER id
       CHARACTER(LEN=200) description
       REAL price
     END STRUCTURE
     
     ! Define two variables, an single record of type ``item''
     ! named ``pear'', and an array of items named ``store_catalog''
     RECORD /item/ pear, store_catalog(100)
     
     ! We can directly access the fields of both variables
     pear.id = 92316
     pear.description = "juicy D'Anjou pear"
     pear.price = 0.15
     store_catalog(7).id = 7831
     store_catalog(7).description = "milk bottle"
     store_catalog(7).price = 1.2
     
     ! We can also manipulate the whole structure
     store_catalog(12) = pear
     print *, store_catalog(12)

This code can easily be rewritten in the Fortran 90 syntax as following:

     ! ``STRUCTURE /name/ ... END STRUCTURE'' becomes
     ! ``TYPE name ... END TYPE''
     TYPE item
       INTEGER id
       CHARACTER(LEN=200) description
       REAL price
     END TYPE
     
     ! ``RECORD /name/ variable'' becomes ``TYPE(name) variable''
     TYPE(item) pear, store_catalog(100)
     
     ! Instead of using a dot (.) to access fields of a record, the
     ! standard syntax uses a percent sign (%)
     pear%id = 92316
     pear%description = "juicy D'Anjou pear"
     pear%price = 0.15
     store_catalog(7)%id = 7831
     store_catalog(7)%description = "milk bottle"
     store_catalog(7)%price = 1.2
     
     ! Assignments of a whole variable do not change
     store_catalog(12) = pear
     print *, store_catalog(12)

GNU Fortran implements STRUCTURES like derived types with the following rules and exceptions:

• Structures act like derived types with the SEQUENCE attribute. Otherwise they may contain no specifiers.
• Structures may share names with other symbols. For example, the following is invalid for derived types, but valid for structures:

            structure /header/
              ! ...
            end structure
            record /header/ header
  

• Structure types may be declared nested within another parent structure. The syntax is:

            structure /type-name/
                ...
                structure [/<type-name>/] <field-list>
            ...
  

  The type name may be ommitted, in which case the structure type itself is anonymous, and other structures of the same type cannot be instantiated. The following shows some examples:

            structure /appointment/
              ! nested structure definition: app_time is an array of two 'time'
              structure /time/ app_time (2)
                integer(1) hour, minute
              end structure
              character(10) memo
            end structure
            
            ! The 'time' structure is still usable
            record /time/ now
            now = time(5, 30)
            
            ...
            
            structure /appointment/
              ! anonymous nested structure definition
              structure start, end
                integer(1) hour, minute
              end structure
              character(10) memo
            end structure
  

• Structures may contain UNION blocks. For more detail see the section on UNION and MAP.
• Structures support old-style initialization of components, like those described in Old-style variable initialization. For array initializers, an initializer may contain a repeat specification of the form <literal-integer> * <constant-initializer>. The value of the integer indicates the number of times to repeat the constant initializer when expanding the initializer list.