(Reading code is not only a basic skill of programmers, but also an indispensable part of the process of software development, maintenance, evolution, review and reuse. This book is the first book that systematically takes reading code as an independent subject. The code cited in this book comes from open source projects - a treasure house that all programmers should cherish. This book focuses on code reading and discusses relevant knowledge and skills in detail. "Stones from other mountains can attack jade". By carefully reading and learning this book, readers can quickly improve their code reading ability and skills, and then draw nutrients from the existing excellent codes, algorithms, frameworks and designs to improve their own development and design ability.This book is suitable for readers who have a certain understanding of the basic knowledge of programming and hope to further improve their own development ability.)