# Misaligned pointer Detects when code accesses a misaligned pointer or creates a misaligned reference. ## Overview In Xcode 9 and later, you can use this check to detect reads from, or writes to, a misaligned pointer, or when you create a misaligned reference. A pointer misaligns if its address isn’t a multiple of its type’s alignment. Dereferencing a misaligned pointer has undefined behavior, and may result in a crash or degraded performance. Alignment violations occur frequently in code that serializes or deserializes data. Avoid this issue by using a serialization format that preserves data alignment. ### Misaligned integer pointer assignment in C In the following example, the `pointer` variable must have 4-byte alignment, but has only 1-byte alignment: ```occ int8_t *buffer = malloc(64); int32_t *pointer = (int32_t *)(buffer + 1); *pointer = 42; // Error: misaligned integer pointer assignment ``` #### Solution Use an assignment function like `memcpy`, which can work with unaligned inputs. ```occ int8_t *buffer = malloc(64); int32_t value = 42; memcpy(buffer + 1, &value, sizeof(int32_t)); // Correct ``` > Note: The compiler can often safely optimize calls to `memcpy`, even for unaligned arguments. ### Misaligned structure pointer assignment in C In the following example, the `pointer` variable must have 8-byte alignment, but has only 1-byte alignment: ```swift struct A { int32_t i32; int64_t i64; }; int8_t *buffer = malloc(32); struct A *pointer = (struct A *)(buffer + 1); pointer->i32 = 7; // Error: pointer is misaligned ``` #### Solution One solution is to pack the structure. In the following example, the packed `A` structure prevents the compiler from adding padding between members: ```occ struct A { ... } __attribute__((packed)); ``` > Important: Packing a structure may adversely impact performance. --- Copyright © 2026 Apple Inc. All rights reserved. | [Terms of Use](https://www.apple.com/legal/internet-services/terms/site.html) | [Privacy Policy](https://www.apple.com/privacy/privacy-policy)