Language Reference

Storage Classes for Variables

Fundamental Storage Classes

All variables are ultimately represented by one of five storage classes:

Automatic

for variables in a procedure that will not be retained once the procedure ends. Variables reside in the stack storage area.

Static

for variables that retain memory throughout the program. Variables reside in the data storage area. Large, uninitialized variables reside in the .bss storage area.

Common

for common block variables. If a common block variable is initialized, the whole block resides in the data storage area; otherwise, the whole block resides in the .bss storage area.

Controlled Automatic

for automatic objects. Variables reside in the stack storage area. XL Fortran allocates storage on entry to the procedure and deallocates the storage when the procedure completes.

Controlled

for allocatable arrays. Variables reside in the heap storage area. You must explicitly allocate and deallocate the storage.

Secondary Storage Classes

None of the following storage classes own their own storage, but are associated with a fundamental storage class at run time.

Pointee

is dependent on the value of the corresponding integer pointer.

Reference parameter

is a dummy argument whose actual argument is passed to a procedure using the default passing method or %REF.

Value parameter

is a dummy argument whose actual argument is passed by value to a procedure.

For details on passing methods, see %VAL and %REF.

Storage Class Assignment

Variable names are assigned storage classes in three ways:

1. Explicitly:
   • Dummy arguments have an explicit storage class of reference parameter or value parameter. See %VAL and %REF for more details.
   • Pointee variables have an explicit storage class of pointee.
   • Variables for which the STATIC attribute is explicitly specified have an explicit storage class of static.
   • Variables for which the AUTOMATIC attribute is explicitly specified have an explicit storage class of automatic.
   • Variables that appear in a COMMON block have an explicit storage class of common.
   • Variables for which the SAVE attribute is explicitly specified have an explicit storage class of static, unless they also appear in a COMMON statement, in which case their storage class is common.
   • Variables that appear in a DATA statement or are initialized in a type declaration statement have an explicit storage class of static, unless they also appear in a COMMON statement, in which case their storage class is common.
   • Function result variables that are of type character or derived have the explicit storage class of reference parameter.
   • Function result variables that do not have the SAVE or STATIC attribute have an explicit storage class of automatic.
   • Automatic objects have an explicit storage class of controlled automatic.
   • Allocatable arrays have an explicit storage class of controlled.

   A variable that does not satisfy any of the above, but that is equivalenced with a variable that has an explicit storage class, inherits that explicit storage class.

   A variable that does not satisfy any of the above, and is not equivalenced with a variable that has an explicit storage class, has an explicit storage class of static if a SAVE statement with no list exists in the scoping unit.

2. Implicitly:

   If a variable does not have an explicit storage class, it can be assigned an implicit storage class as follows:

   • Variables whose names begin with a letter, dollar sign or underscore that appears in an IMPLICIT STATIC statement have a storage class of static.
   • Variables whose names begin with a letter, dollar sign or underscore that appears in an IMPLICIT AUTOMATIC statement have a storage class of automatic.

   In a given scoping unit, if a letter, dollar sign or underscore has not been specified in an IMPLICIT STATIC or IMPLICIT AUTOMATIC statement, the implicit storage class is the same as that in the host.

   Variables declared in the specification part of a module are associated with the static storage class.

   A variable that does not satisfy any of the above but that is equivalenced with a variable that has an implicit storage class, inherits that implicit storage class.

3. Default:

   All other variables have the default storage class:

   • Static, if you specified the -qsave compiler option.
   • Automatic, if you specified the -qnosave compiler option. This is the default setting.

     See "-qsave Option" in the User's Guide for details on the default settings with regard to the invocation commands.