Understanding Objective‑C Object Memory Layout and Alignment
This article explores how Objective‑C objects are converted to low‑level C/C++ structures, compares the results of class_getInstanceSize, malloc_size and sizeof, and explains memory‑alignment rules, member ordering, padding, and inheritance effects on the actual memory footprint of iOS objects.
The article explains how Objective‑C objects are transformed into C/C++ structures, examines APIs such as class_getInstanceSize , malloc_size and the sizeof operator to measure object size, and details the rules of memory alignment on 64‑bit iOS.
It provides step‑by‑step examples, including clang command output and struct definitions for NSObject_IMPL and custom classes, and demonstrates how member order, padding, and inheritance affect the final allocated size, with visual diagrams and reference links.
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