Re: RE : [fpc-pascal] How are Assigned, Free, Nil and Destroy related?
On 22 October 2011 08:14, Ludo Brands ludo.bra...@free.fr wrote: Nil is not a routine, it is a value, it means that the object is empty, it does not exist / is not allocated. Nil in existing implementations that I know is represented by the value zero. The typical life-cycle of a object is: MyObject := TMyObject.Create; try MyObject.DoSomething(); finally MyObject.Free; end; One pitfall: the variable MyObject before MyObject := TMyObject.Create; is undefined and not necessarily nil. Variables are not initialized by default and can contain anything. In general, MyObject.Free does not set MyObject to nil neither. Good practice is to initialize pointer variables to nil and resetting them to nil after freeing them whenever assigned() or nil is going to be used. Does that mean that Free itself reclaims the memory used by the object's fields and properties but does not release the memory used by the TObject or pointer itself, where as setting it to nil or executing Destroy does, or does Destroy do something different? Ludo ___ fpc-pascal maillist - fpc-pascal@lists.freepascal.org http://lists.freepascal.org/mailman/listinfo/fpc-pascal -- Frank Church === http://devblog.brahmancreations.com ___ fpc-pascal maillist - fpc-pascal@lists.freepascal.org http://lists.freepascal.org/mailman/listinfo/fpc-pascal
RE : RE : [fpc-pascal] How are Assigned, Free, Nil and Destroy related?
Does that mean that Free itself reclaims the memory used by the object's fields and properties but does not release the memory used by the TObject or pointer itself, where as setting it to nil or executing Destroy does, or does Destroy do something different? All memory is released including TObject but the variable pointing to the TObject (fe: SCStrings) isn't set to nil. It still points to where the TObject was. Warning: setting a TObject variable to nil does not free the object unless it is reference counted! Strings and COM style interfaces are reference counted. Pascal is not VB. Ludo ___ fpc-pascal maillist - fpc-pascal@lists.freepascal.org http://lists.freepascal.org/mailman/listinfo/fpc-pascal
Re: RE : [fpc-pascal] How are Assigned, Free, Nil and Destroy related?
On Sat, Oct 22, 2011 at 9:36 AM, Frank Church vfcli...@gmail.com wrote: Does that mean that Free itself reclaims the memory used by the object's fields and properties but does not release the memory used by the TObject or pointer itself, where as setting it to nil or executing Destroy does, or does Destroy do something different? No, you got parts of it wrong: *Free calls Destroy which releases the memory of the object itself. *Nothing releases the memory of the pointer to the object. You don't want to release the 4 or 8 bytes of the pointer. If you did release it, then your application would crash when trying to read the pointer to check if it is nil. *Destroy implements releasing the memory of the object. Free calls Destroy. *Setting the object to nil does just that. It changes the pointer to the object to have the value nil (zero). It does not release the pointer. -- Felipe Monteiro de Carvalho ___ fpc-pascal maillist - fpc-pascal@lists.freepascal.org http://lists.freepascal.org/mailman/listinfo/fpc-pascal
