---
title: Use of deallocated memory
framework: xcode
role: article
role_heading: Article
path: xcode/use-of-deallocated-memory
---

# Use of deallocated memory

Detects the use of deallocated memory.

## Overview

Overview Use this check to detect when your code accesses deallocated memory, which can lead to unpredictable behavior. Available in Xcode 7 and later. Use of deallocated memory in Objective-C In the following example, the unsafePointer variable has __unsafe_unretained ownership. Because there are no other objects that have a strong reference to it, the autorelease pool deallocates the variable, causing it to point to invalid memory. __unsafe_unretained MyClass *unsafePointer; @autoreleasepool {         MyClass *object = [MyClass new];     unsafePointer = object; } NSLog(@"%d", unsafePointer->instanceVariable);  // Error: unsafePointer is deallocated in autorelease pool Solution Use a __strong or __weak reference instead of __unsafe_unretained. Strong ownership ensures that you, or the system, can only deallocate an object when no strong references exist. Weak ownership has no effect on the life cycle of the object it refers to, but ensures that a variable is nil when you deallocate the object, or the system deallocates it. Use of deallocated pointer in Objective-C This issue exists when using pointers to nonobject types, as well. In the following example, the pointer to the instance variable invalidates when deallocating the object: int *unsafePointer; @autoreleasepool {         MyClass *object = [MyClass new];     unsafePointer = &object->instanceVariable; } NSLog(@"%d", *unsafePointer); // Error: unsafePointer is invalidated when object is deallocated in autorelease pool Solution Use property accessors rather than direct access to instance variables and pointers whenever possible.

## See Also

### Address Sanitizer

- [Deallocation of deallocated memory](xcode/deallocation-of-deallocated-memory.md)
- [Deallocation of nonallocated memory](xcode/deallocation-of-nonallocated-memory.md)
- [Use of stack memory after function return](xcode/use-of-stack-memory-after-function-return.md)
- [Use of out-of-scope stack memory](xcode/use-of-out-of-scope-stack-memory.md)
- [Overflow and underflow of buffers](xcode/overflow-and-underflow-of-buffers.md)
- [Overflow of C++ containers](xcode/overflow-of-c-containers.md)