POINTER - Compaq Fortran

Statement: Establishes pairs of variables and pointers, in which each pointer contains the address of its paired variable. This statement is different from the Fortran 95/90 POINTER statement.

Syntax

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 ia32 systems, a pointer occupies one numeric storage unit, so it is a 32-bit quantity (INTEGER(4)). On Alpha and ia64 systems, a pointer occupies two numeric storage units, so it is a 64-bit quantity (INTEGER(8)).
  
  
• 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:
  
  INTEGER I(10)                INTEGER I(10)
  INTEGER I1(10) /10*10/       POINTER (P,I)
  POINTER (P,I)                P = MALLOC(40)
  P = %LOC(I1)                 I(2) = I(2) + 1
  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 (Compaq Fortran) 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.

Compatibility

CONSOLE STANDARD GRAPHICS QUICKWIN GRAPHICS WINDOWS DLL LIB

See Also: LOC, MALLOC, FREE

Example

 POINTER (p, k)
 INTEGER j(2)

 ! This has the same effect as j(1) = 0, j(2) = 5
 p = LOC(j)
 k = 0
 p = p + SIZEOF(k) ! 4 for 4-byte integer
 k = 5