B.11 The Compaq Fortran POINTER Statement

The POINTER statement discussed here is different from the one discussed in Section 5.15. It establishes pairs of variables and pointers, in which each pointer contains the address of its paired variable.

This POINTER statement takes the following form:

POINTER (pointer, pointee) [, (pointer, pointee)] . . .

pointer
Is a variable whose value is used as the address of the pointee.

pointee
Is a variable; it can be an array name or array specification.

Rules and Behavior

The following are pointer rules and behavior:

• Two pointers can have the same value, so pointer aliasing is allowed.
  
  
• When used directly, a pointer is treated like an integer variable. On Alpha and ia64 processors, a pointer occupies two numeric storage units, so it is a 64-bit quantity (INTEGER(8)). On ia32 processors, a pointer occupies one numeric storage unit, so it is a 32-bit quantity (INTEGER(4)).
  
  
• A pointer cannot be a pointee.
  
  
• A pointer cannot appear in an ASSIGN statement and cannot have the following attributes:
  
  

  ALLOCATABLE	INTRINSIC	POINTER
  EXTERNAL	PARAMETER	TARGET

  A pointer can appear in a DATA statement with integer literals only.

• Integers can be converted to pointers, so you can point to absolute memory locations.
  
  
• A pointer variable cannot be declared to have any other data type.
  
  
• A pointer cannot be a function return value.
  
  
• You can give values to pointers by doing the following:
  
  
  • Retrieve addresses by using the LOC intrinsic function (or the %LOC built-in function)
    
    
  • Allocate storage for an object by using the MALLOC intrinsic function (or by using malloc(3f) on Tru64 UNIX or Linux systems, or LIB$GET_VM on OpenVMS systems)

  For example:

  Using %LOC:                  Using MALLOC:          Using LIB$GET_VM:
  
  INTEGER I(10)                INTEGER I(10)          INTEGER I(10)
  INTEGER I1(10) /10*10/       POINTER (P,I)          INTEGER LIB$GET_VM,STATUS
  POINTER (P,I)                P = MALLOC(40)         POINTER (P,I)
  P = %LOC(I1)                 I(2) = I(2) + 1        STATUS = LIB$GET_VM(P,40)
  I(2) = I(2) + 1                                     IF (.NOT. STATUS) CALL EXIT(STATUS)
                                                      I(2) = I(2) + 1
  

• The value in a pointer is used as the pointee's base address.

The following are pointee rules and behavior:

• A pointee is not allocated any storage. References to a pointee look to the current contents of its associated pointer to find the pointee's base address.
  
  
• A pointee cannot be data-initialized or have a record structure that contains data-initialized fields.
  
  
• A pointee can appear in only one POINTER statement.
  
  
• A pointee array can have fixed, adjustable, or assumed dimensions.
  
  
• A pointee cannot appear in a COMMON, DATA, EQUIVALENCE, or NAMELIST statement, and it cannot have the following attributes:
  
  

  ALLOCATABLE	OPTIONAL	SAVE
  AUTOMATIC	PARAMETER	STATIC
  INTENT	POINTER	TARGET

  
  
• A pointee cannot be:
  
  
  • A dummy argument
    
    
  • A function return value
    
    
  • A record field or an array element
    
    
  • Zero-sized
    
    
  • An automatic object
    
    
  • The name of a generic interface block
  
  
• If a pointee is of derived type, it must be of sequence type.