USE

USE [[, mod-nature] ::] name [, rename-list]

USE [[, mod-nature] ::] name, ONLY : [ only-list]

Description

If the USE statement is specified without the ONLY option, the program unit has access to all public entities in the named module.

If the USE statement is specified with the ONLY option, the program unit has access to only those entities following the option.

If more than one USE statement for a given module appears in a scoping unit, the following rules apply:

• If one USE statement does not have the ONLY option, all public entities in the module are accessible, and any rename-lists and only-lists are interpreted as a single, concatenated rename-list.

• If all the USE statements have ONLY options, all the only-lists are interpreted as a single, concatenated only-list. Only those entities named in one or more of the only-lists are accessible.

If two or more generic interfaces that are accessible in a scoping unit have the same name, the same operator, or are both assignments, they are interpreted as a single generic interface. Otherwise, multiple accessible entities can have the same name only if no reference to the name is made in the scoping unit.

The local names of entities made accessible by a USE statement must not be respecified with any attribute other than PUBLIC or PRIVATE. The local names can appear in namelist group lists, but not in a COMMON or EQUIVALENCE statement.

Example

The following shows examples of the USE statement:

MODULE MOD_A
  INTEGER :: B, C
  REAL E(25,5), D(100)
END MODULE MOD_A
...
SUBROUTINE SUB_Y
  USE MOD_A, DX => D, EX => E   ! Array D has been renamed DX and array E
  ...                           ! has been renamed EX. Scalar variables B
END SUBROUTINE SUB_Y            ! and C are also available to this 
...                             ! subroutine (using their module names).
SUBROUTINE SUB_Z
  USE MOD_A, ONLY: B, C         ! Only scalar variables B and C are
  ...                           !   available to this subroutine
END SUBROUTINE SUB_Z
...

You must not specify a user module and an intrinsic module of the same name in the same program unit. For example, if you specify a user module named ISO_FORTRAN_ENV, then it is illegal to specify the following in the same program unit:

USE :: ISO_FORTRAN_ENV
USE, INTRINSIC :: ISO_FORTRAN_ENV

The following example shows a module containing common blocks:

MODULE COLORS
  COMMON /BLOCKA/ C, D(15)
  COMMON /BLOCKB/ E, F
  ...
END MODULE COLORS
...
FUNCTION HUE(A, B)
  USE COLORS
  ...
END FUNCTION HUE

The USE statement makes all of the variables in the common blocks in module COLORS available to the function HUE.

To provide data abstraction, a user-defined data type and operations to be performed on values of this type can be packaged together in a module. The following example shows such a module:

MODULE CALCULATION
  TYPE ITEM
    REAL :: X, Y
  END TYPE ITEM

  INTERFACE OPERATOR (+)
    MODULE PROCEDURE ITEM_CALC
  END INTERFACE

CONTAINS
  FUNCTION ITEM_CALC (A1, A2)
    TYPE(ITEM) A1, A2, ITEM_CALC
    ...
  END FUNCTION ITEM_CALC
  ...
END MODULE CALCULATION

PROGRAM TOTALS
USE CALCULATION
TYPE(ITEM) X, Y, Z
  ...
  X = Y + Z
  ...
END

The USE statement allows program TOTALS access to both the type ITEM and the extended intrinsic operator + to perform calculations.

The following shows another example:

 ! Module containing original type declarations
 MODULE geometry
 type square
    real side
    integer border
 end type
 type circle
    real radius
    integer border
 end type
 END MODULE

 ! Program renames module types for local use.
 PROGRAM test
 USE GEOMETRY,LSQUARE=>SQUARE,LCIRCLE=>CIRCLE
 ! Now use these types in declarations
 type (LSQUARE) s1,s2
 type (LCIRCLE) c1,c2,c3

The following shows a defined operator in a USE statement:

  USE mymod, OPERATOR(.localop.) => OPERATOR(.moduleop.)

Entities in modules can be accessed either through their given name, or through aliases declared in the USE statement of the main program unit. For example:

  USE MODULE_LIB, XTABS => CROSSTABS 

This statement accesses the routine called CROSSTABS in MODULE_LIB by the name XTABS. This way, if two modules have routines called CROSSTABS, one program can use them both simultaneously by assigning a local name in its USE statement.

When a program or subprogram renames a module entity, the local name (XTABS, in the preceding example) is accessible throughout the scope of the program unit that names it.

The ONLY option also allows public variables to be renamed. Consider the following:

  USE MODULE_A, ONLY: VARIABLE_A => VAR_A 

In this case, the host program accesses only VAR_A from module A, and refers to it by the name VARIABLE_A.

Consider the following example:

  MODULE FOO
     integer foos_integer
   PRIVATE
     integer foos_my_integer
  END MODULE FOO

PRIVATE, in this case, makes the PRIVATE attribute the default for the entire module FOO. To make foos_integer accessible to other program units, add the line:

  PUBLIC :: foos_integer 

Alternatively, to make only foos_my_integer inaccessible outside the module, rewrite the module as follows:

  MODULE FOO
    integer foos_integer
    integer, private::foos_my_integer
  END MODULE FOO