Mega Code Archive

Nil - a pointer value that is defined as undetermined

const Nil = Pointer(0); Description The Nil constant is a pointer value that is defined as undetermined. Use of a Nil pointer will result in an exception. Nil is mostly used as a substitute for a Pointer parameter - it tells the routine that no Pointer value is available for this parameter. Pointer variables are not set to Nil except in special circumstances, such as when creating a new object that contains pointers. This is because Delphi initialises the storage taken by a new object to 0's. A Nil pointer is one that has the value 0. Related commands Assigned Returns true if a reference is not nil Null A variable that has no value Pointer Defines a general use Pointer to any memory based data Example code : A simple example var myPtr : PChar; begin // Pointer variables are not set to nil by default if myPtr = Nil then ShowMessage('myPtr is nil') else ShowMessage('myPtr is not nil'); // So we must set them to nil to be sure that they are undefined myPtr := Nil; if myPtr = Nil then ShowMessage('myPtr is nil') else ShowMessage('myPtr is still not nil'); end; Show full unit code myPtr is not nil myPtr is nil