## 3.2.1 Derived-Type Definition

A derived-type definition specifies the name of a user-defined type and the types of its components. It takes the following form:

  TYPE [ [, access] :: ] name
  component-definition
  [component-definition] . . .
  END TYPE [name]
  access
  Is the PRIVATE or PUBLIC keyword. The keyword can only be specified if the derived-type definition is in the specification part of a module.
  name
  Is the name of the derived type. It must not be the same as the name of any intrinsic type, or the same as the name of a derived type that can be accessed from a module.
  component-definition
  Is one or more type declaration statements defining the component of derived type.

  The first component definition can be preceded by an optional PRIVATE or SEQUENCE statement. (Only one PRIVATE or SEQUENCE statement can appear in a given derived-type definition.)

  PRIVATE specifies that the components are accessible only within the defining module, even if the derived type itself is public.

  SEQUENCE cause the components of the derived type to be stored in the same sequence they are listed in the type definition. If SEQUENCE is specified, all derived types specified in component definitions must be sequence types.

  A component definition takes the following form:

    type [ [, attr] ::] component [(a-spec)] [ *char-len] [init-ex]
    type
    Is a type specifier. It can be an intrinsic type or a previously defined derived type. (If the POINTER attribute follows this specifier, the type can also be any accessible derived type, including the type being defined.)
    attr
    Is an optional POINTER attribute for a pointer component, or an optional DIMENSION attribute for an array component. You can specify one or both attributes. If DIMENSION is specified, it can be followed by an array specification.

    The POINTER or DIMENSION attribute can only appear once in a given component-definition.

    component
    Is the name of the component being defined.
    a-spec
    Is an optional array specification, enclosed in parentheses. If POINTER is specified, the array is deferred shape; otherwise, it is explicit shape. In an explicit-shape specification, each bound must be a constant scalar integer expression. For more information on array specifications, see Section 5.1.4.

    If the array bounds are not specified here, they must be specified following the DIMENSION attribute.

    char-len
    Is an optional scalar integer literal constant; it must be preceded by an asterisk (*). This parameter can only be specified if the component is of type CHARACTER.
    init-ex
    Is an initialization expression or, for pointer components, =>NULL( ). This is a Fortran 95 feature.

    If init-ex is specified, a double colon must appear in the component definition. The equals assignment symbol (=) can only be specified for nonpointer components.

    The initialization expression is evaluated in the scoping unit of the type definition.

Rules and Behavior

If a name is specified following the END TYPE statement, it must be the same name that follows TYPE in the derived type statement.

A derived type can be defined only once in a scoping unit. If the same derived-type name appears in a derived-type definition in another scoping unit, it is treated independently.

A component name has the scope of the derived-type definition only. Therefore, the same name can be used in another derived-type definition in the same scoping unit.

Two data entities have the same type if they are both declared to be of the same derived type (the derived-type definition can be accessed from a module or a host scoping unit).

If the entities are in different scoping units, they can also have the same derived type if they are declared with reference to different derived-type definitions, and if both derived-type definitions have all of the following:

- The same name
- A SEQUENCE statement (they both have sequence type)
- Components that agree in name, order, and attributes; components cannot be private

For More Information:

- On intrinsic data types, see Section 3.1.
- On how to declare variables of derived type, see Section 5.1.3.
- On arrays, see Section 3.4.2.
- On pointers, see Section 5.15.
- On structure components, see Section 3.2.3.
- On default initialization for derived-type components, see Section 3.2.2.
- On alignment of derived-type data components, see your user manual or programmer's guide.

Previous Page Next Page Table of Contents