I am trying to do project with Manual Memory Management in Objective-c. I disabled ARC. I developed custom data structure LinkedList how can I dealloc this data structure? Should I use dealloc or release for dealloc object? When I tried dealloc it return me error. Is any memory profiler in xcode?
With manual memory management you call release when you no longer require an object you own.
The dealloc method of an object is called by the system before it is destroyed, it can be used to do cleanup. A dealloc method in manual memory management must call [super dealloc] - this is different from ARC where the super method must not be called.
HTH
Related
Which is the best method
Override "release" or "dealloc" method in objective c?
why?
Under non-ARC, 99% of the cases you should not override the release method.
I have seen only 1 case that the need to override the release method - a kind of singleton, which forces the class have really 1 single instance no matter how many times you call alloc.
That way override not only the release method, but also allowWithZone:, retain, 'retainCount`, etc. (It is actually not common to implement that kind of singleton)
Which is the best method? Override the release or the dealloc method?
- dealloc, definitely. You should never override - release.
Why?
One, because release does a bunch of internal stuff. Two, because if release is called, it does not mean that the object is deallocated.
So you would release your ivars or null your properties by accident. And who wants an ugly segfault when we can have worldpeace instead?
If an object is really deallocated, - dealloc will be called.
If you are not using ARC, you should override the -[MyObject dealloc] dealloc method to release all retained objects inside your object. I have never found a case where I needed to override the release method.
If you are using ARC, you can usually avoid overriding the -dealloc method at all, unless you are using anything that ARC won't free up like a sqlite pointer or something.
dont override either for anything not relating to memory management - you dont when and if those methods even get called.
exceptions for when you should dealloc:
removing KVO / notification center observer
deallocating manually allocated memory (arc) / release your ivars (non-arc)
My Question is When the dealloc method will cal before the application termination, If it happens , When the application terminates all the memory of the objects and application will be removed from memory, then what is the use of writing dealloc method?
This is a general question about memory management. You use dealloc in Objective-C, free in C etc. to clean the memory allocated for the variables that are no longer in use. When the application terminates of course all of the memory allocated by the application will be released. However, if your application keeps allocating memory as it runs, and if the user runs the application for long enough, unless you release unused memory, the device's memory would get eventually used up. This is why you need to use dealloc.
The dealloc method describes how the object will be released. When an object is being deallocated unless you override the dealloc method only the object's pointer will be released. Therefore, in order to release properties and fields in your object you need to manually release them in your dealloc method.
Is it good practice for an object in Objective-C to commit suicide? That is, for an object to declare [self dealloc] where -dealloc permits an orderly wind down as usual? What are the principal risks?
As it happens I have a specific example, a custom timer object that extends NSObject and comprises an NSTimer instance and an NSUInteger which is set to limit the number of times the timer fires. When time is up the object tells the timer to -invalidate and then commits suicide by calling its -dealloc method. As this is automatic we have no worries about having to track the object or crucially knowing when is the correct moment to deallocate it.
For a more detailed explanation see my post over here.
You shouldn't be calling -dealloc. Instead call [self release] so the reference count goes to 0 and let the system call -dealloc.
Is it good practice for an object in Objective-C to commit suicide? That is, for an object to declare [self dealloc] where -dealloc permits an orderly wind down as usual? What are the principal risks?
No.
The only time you should ever write a call to dealloc is to send dealloc to the super object in the dealloc method of one of your classes. No exceptions.
If you try to send dealloc to an object at any other time, you risk leaving other objects with dangling pointers. Don't do it.
Should you ever send release to self? That is a different matter, but you should still follow the Memory Management Rules. If you have sent retain to self, then at some point you will need to send release to self. There is one exception which is in init, if initialisation fails you have to release self and return nil (I guess you could claim that alloc has sent retain to self).
Can someone explain the differences between free(), release, autorelease and dealloc?
free() is a C function that you use to dispose of no longer needed memory you obtained through malloc() or other function that is documented to require free() to deallocate its memory e.g. strdup().
-dealloc is an Objective-C selector that is sent by the Objective-C runtime to an object when the object is no longer owned by any part of the application.
-release is the selector you send to an object to indicate that you are relinquishing ownership of that object. Once an object is not owned by anybody, it is sent the -dealloc message by the runtime.
-autorelease is a selector you send to an object to indicate you are relinquishing ownership of the object. However if nobody now owns the object the final -dealloc will be deferred until some unspecified later point. In fact, what you are really doing is transferring your ownership to an autorelease pool which will then release it when it is itself released (or drained).
You must never send -dealloc to an object except to super in the object's own -dealloc method.
Out of the 4 methods you've mentioned you'll typically only use release and autorelease in objective-c. free maybe used when you've used c and malloc otherwise you should use release and autorelease.
dealloc shouldn't be called by any of your code as it can interfere with the retain/release cycle that objective-c uses to keep track of resources. Using dealloc will almost certainly result in crashes at runtime if you ever use it.
The ultimate resource of the use of the release and autorelease is the Apple memory management documentation
free is the opposite of malloc and is used in C. You'll likely not use it very much programming in Objective C
If you own an object, you release it when you're done with it
You can also autorelease an object. This automatically releases it at the end of the current run loop iteration
When the reference count on an object drops to zero, the runtime calls dealloc. You should not call this method yourself
You "own" an object if you alloc, new, retain or copy it.
Apple provide some good documentation on this.
When deallocing a refrence I've seen release and dealloc being used for example
-(void)dealloc
{
[foo release];
[nar dealloc];
[super dealloc];
}
My question is when is release to be used and when is dealloc to be used?
Thanks
Never call dealloc except as [super dealloc] at the end of your class's dealloc method. The release method relinquishes ownership of an object. When a Cocoa object no longer has any owners, it may be deallocated — in which case it will automatically be sent a dealloc message.
If you're going to program Cocoa, you need to read the Memory Management Guidelines. It's incredibly simple once you get over the initial hump, and if you don't understand what's in that document, you'll have lots of subtle bugs.
The dealloc statement in your example is called when the object's retain count becomes zero (through an object sending it a release message).
As it is no longer needed, it cleans itself up by sending a release message to the objects that it is holding on to.
You're never supposed to call dealloc explicitly (unless it's [super dealloc] within the dealloc method, but that's the only exception). Objective-C handles memory management via reference counting, so you're simply supposed to match your allocs/retains with releases/autoreleases and let the object deconstruct itself.