Data types whose values are addresses in memory.

Pointers are Variables whose values are addresses in memory, and they are said to 'point' to this memory. The type of data that is pointed to depends on the type of pointer (an Integer Pointer points to Integer data). Pointers are declared like any other variable, with the suffix "pointer" or "ptr" following the type name.

Assigning pointer variables
A pointer is a memory address and the value of the pointer itself is that memory address. To assign a pointer variable is to assign it a memory address to something. One way to assign a pointer a memory address is to take the address of some other variable in the program using Operator @ (Address of).

Accessing pointed to data
The data pointed to by a pointer can be accessed with Operator * (Value of). This operator returns a reference to the data that its operand points to. The following,

Dim myInteger As Integer = 10
Dim myPointer As Integer Pointer = @myInteger
*myPointer = 20
Print myInteger
defines an Integer variable called myInteger and an Integer pointer called myPointer that points to the location in memory where myInteger is stored. Operator @ (Address of) is used to retrieve the address of myInteger. The value of 20 is assigned to the location at which myPointer points - the address of myInteger, or @myInteger. Changes to *myPointer directly affect the value of myInteger (the expression "*myPointer" is the same thing as "myInteger").

Pointers to user-defined types
Pointers to user-defined types are defined and used like all other pointers. Accessing a member of a Type or Class requires one of the following two methods:

Type myType
    a As Integer
    b As Double
End Type

Dim x As myType
Dim p As myType Pointer = @x

'' 1) dereference the pointer and use the member access operator:
(*p).a = 10
(*p).b = 12.34

'' 2) use the shorthand form of the member access operator:
Print p->a
Print p->b
The first method uses Operator . (Member access). This operator accesses members from references, so the pointer is dereferenced first. The member access operator has higher priority over the dereference operator, so parenthesis are needed to dereference the pointer before using it with the member access operator.

The second method uses Operator -> (Pointer to member access). This operator accesses members from pointers, which are automatically dereferenced. This can make code a little clearer, although both forms produce identical results.

See also:
Back to Programmer's Guide
Valid XHTML :: Valid CSS: :: Powered by WikkaWiki

sf.net phatcode