---
title: Null reference creation and null pointer dereference
framework: xcode
role: article
role_heading: Article
path: xcode/null-reference-creation-and-null-pointer-dereference
---

# Null reference creation and null pointer dereference

Detects the creation of null references and null pointer dereferences.

## Overview

Overview In Xcode 9 and later, you can use this check to detect the creation of null references and null pointer dereferences. Dereferencing a null pointer always results in undefined behavior and can cause crashes. If the compiler finds a pointer dereference, it treats that pointer as nonnull. As a result, the optimizer may remove null equality checks for dereferenced pointers. Creating a null reference in C++ The following example demonstrates how to create a null reference. References in C++ must be nonnull: int &x = *(int *)nullptr; // Error: null reference Solution Use a pointer instead. int *x = nullptr; // Correct Member access through a null pointer in C++ The following code makes a member call on an object with a null address. The compiler may remove the null check on the this pointer because it requires the pointer to be nonnull. struct A {     int x;     int getX() {         if (!this) { // Warning: redundant null check may be removed             return 0;         }         return x; // Warning: 'this' pointer is null, but is dereferenced here     } }; A *a = nullptr; int x = a->getX(); // Error: member access through null pointer important: Always avoid null checks on the this pointer. Solution Avoid calling methods on null objects.

## See Also

### Undefined Behavior Sanitizer

- [Misaligned pointer](xcode/misaligned-pointer.md)
- [Invalid Boolean value](xcode/invalid-boolean.md)
- [Out-of-bounds array access](xcode/out-of-bounds-array-access.md)
- [Invalid enumeration value](xcode/invalid-enumeration-value.md)
- [Reaching of unreachable point](xcode/reaching-of-unreachable-point.md)
- [Dynamic type violation](xcode/dynamic-type-violation.md)
- [Invalid float cast](xcode/invalid-float-cast.md)
- [Division by zero](xcode/division-by-zero.md)
- [Nonnull argument violation](xcode/nonnull-argument-violation.md)
- [Nonnull return value violation](xcode/nonnull-return-value-violation.md)
- [Nonnull variable assignment violation](xcode/nonnull-variable-assignment-violation.md)
- [Invalid object size](xcode/invalid-object-size.md)
- [Invalid shift](xcode/invalid-shift.md)
- [Integer overflow](xcode/integer-overflow.md)
- [Invalid variable-length array](xcode/invalid-variable-length-array.md)