To see how pointers work, look at the following example.

 1         var
 2           X, Y: Integer;  // X and Y are Integer variables
 3           P: ^Integer     // P points to an Integer
 4           begin
 5             X := 17;      // assign a value to X
 6             P := @X;      // assign the address of X to P
 7             Y := P^;      // dereference P; assign the result to Y
 8           end;

Line 2 declares X and Y as variables of type Integer. Line 3 declares P as a pointer to an Integer value; this means that P can point to the location of X or Y. Line 5 assigns a value to X, and line 6 assigns the address of X (denoted by @X) to P. Finally, line 7 retrieves the value at the location pointed to by P (denoted by ^P) and assigns it to Y. After this code executes, X and Y have the same value, namely 17. 

The @ operator, which we have used here to take the address of a variable, also operates on functions and procedures. For more information, see The @ operator and Procedural types in statements and expressions. 

The symbol ^ has two purposes, both of which are illustrated in our example. When it appears before a type identifier 

^typeName 

it denotes a type that represents pointers to variables of type typeName. When it appears after a pointer variable 

pointer^ 

it dereferences the pointer; that is, it returns the value stored at the memory address held by the pointer. 

Our example may seem like a roundabout way of copying the value of one variable to another - something that we could have accomplished with a simple assignment statement. But pointers are useful for several reasons. First, understanding pointers will help you to understand the Delphi language, since pointers often operate behind the scenes in code where they don't appear explicitly. Any data type that requires large, dynamically allocated blocks of memory uses pointers. Long-string variables, for instance, are implicitly pointers, as are class instance variables. Moreover, some advanced programming techniques require the use of pointers.

type
  PInteger = ^Integer;
var
  R: Single;
  I: Integer;
  P: Pointer;
  PI: PInteger;
begin
  ...
  P := @R;
  PI := PInteger(P);
  I := PI^;
end;

Of course, reals and integers are stored in different formats. This assignment simply copies raw binary data from R to I, without converting it. 

In addition to assigning the result of an @ operation, you can use several standard routines to give a value to a pointer. The New and GetMem procedures assign a memory address to an existing pointer, while the Addr and Ptr functions return a pointer to a specified address or variable. 

Dereferenced pointers can be qualified and can function as qualifiers, as in the expression P1^.Data^. 

The reserved word nil is a special constant that can be assigned to any pointer. When nil is assigned to a pointer, the pointer doesn't reference anything.

You can declare a pointer to any type, using the syntax 

type pointerTypeName = ^type 

When you define a record or other data type, it might be useful to also to define a pointer to that type. This makes it easy to manipulate instances of the type without copying large blocks of memory.

The fundamental types PAnsiChar and PWideChar represent pointers to AnsiChar and WideChar values, respectively. The generic PChar represents a pointer to a Char (that is, in its current implementation, to a WideChar). These character pointers are used to manipulate null-terminated strings. (See Working with null-terminated strings.)

The fundamental type PByte represents a pointer to any byte data that is not character data. This type is declared with the {$POINTERMATH ON} compiler directive.

function TCustomVirtualStringTree.InternalData(Node: PVirtualNode): Pointer;
begin
    if (Node = FRoot) or (Node = nil) then
        Result := nil
    else
        Result := PByte(Node) + FInternalDataOffset;
end;

The $T compiler directive controls the types of pointer values generated by the @ operator. This directive takes the form of:

{$T+} or {$T-}

In the {$T-} state, the result type of the @ operator is always an untyped pointer that is compatible with all other pointer types. When @ is applied to a variable reference in the {$T+} state, the type of the result is ^T, where T is compatible only with pointers to the type of the variable.

The System and SysUtils units declare many standard pointer types that are commonly used. 

Use the {POINTERMATH <ON|OFF>} directive to turn pointer arithmetic on or off for all typed pointers, so that increment/decrement is by element size.  

Selected pointer types declared in System and SysUtils  

Data Types 

Simple Types 

String Types 

Structured Types 

Procedural Types 

Variant Types 

Type Compatibility and Identity 

Declaring Types 

Variables 

Declared Constants 

Enabling Unicode in Your Applications 

Unicode in RAD Studio