Delphi Basics : Assigned command

DelphiBasics

Assigned
Function

Returns true if a reference is not nil

System unit

1	function Assigned(PointerName Pointer):Boolean;
2	function Assigned (ObjectName TObject:Boolean;
3	function Assigned (MethodName Method:Boolean;

Description

The Assigned function checks to see if a reference is not nil. It returns True if not nil, and False if nil.

Use of a Nil reference will result in an exception.

The three versions of Assigned allow the function to work on data pointers, object references, and class method references.

It is better to use Assigned rather than Nil when referring to methods so as to distinguish from the checking of a nil result of a method.

Related commands

Nil		A pointer value that is defined as undetermined
Pointer		Defines a general use Pointer to any memory based data

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Example code : A simple example

var
  myPtr : PChar;

begin
  // Pointer variables are not set to nil by default
  if Assigned(myPtr)
  then ShowMessage('myPtr is not nil')
  else ShowMessage('myPtr is nil');

  // So we must set them to nil to be sure that they are undefined
  myPtr := Nil;
  if Assigned(myPtr)
  then ShowMessage('myPtr is still not nil')
  else ShowMessage('myPtr is nil');
end;

Show full unit code

myPtr is not nil
myPtr is nil