[ < ] [ > ]   [ << ] [ Up ] [ >> ]         [Top] [Contents] [Index] [ ? ]

9.174 Null

Synopsis

 
var
  Null: Void absolute 0;

Description

`Null' is a predefined variable at address `nil'. `Null' can be passed as a "void" argument to a procedure, function or operator expecting a "var" parameter. Note: Make sure they can handle this case, otherwise this is likely to cause an exception and the program will be terminated. Since `Null' is an L-value, it can be taken as "nil-reference".

Conforming to

`Null' is a Borland Delphi extension.

Example

 
program NullDemo;
type
  PString = ^String;
var
  Com1: String (25) = 'This is an amazing number';
  Com2: String (25) = 'This is a boring number';

procedure FooBar (Foo: Integer; var Comment: PString); begin if Odd (Foo) then WriteLn ('FooBar:', Foo, ' is odd') else WriteLn ('FooBar:', Foo, ' is even'); if @Comment <> nil then if not Odd(foo) then Comment := @Com1 else Comment := @Com2 end;

var S: String (25); P: PString value @S;

begin { FooBar allows you to leave out variables for any information you might not need } FooBar (1, Null); { But FooBar is flexible, after all } FooBar (6, p); WriteLn ('FooBar said about 6: `', P^, '''') end.

See also

section 9.172 nil



This document was generated by Frank Heckenbach on May, 10 2002 using texi2html