Chapter 10: Organization and documentation

Introduction

This introduction explains why useful documentation distinguishes an interface’s purpose from its implementation details and why code and comments should each contribute meaningful information.

• Useful code explanations: Explain why names and comments should help readers understand code rather than obscure it or repeat what is obvious.
  Why it matters: A future reader—including you—needs clues about the code’s meaning, not commentary that adds no information.
• Four levels of explanation: Distinguish what an interface does, what a function is for, how its code is organized, and the manner in which implementation details work.
  Why it matters: The distinction helps you put the most important information where the most readers will find it.
• Interface and implementation separation: Explain why interface documentation and implementation explanation should be kept distinct, and identify the C file kinds the section associates with that separation.
  Why it matters: Separating these explanations lets users find the interface information they need without reading implementation details.

Key terms: magic constants, comments, function name, variable name, what, what for, how, in which manner, function interfaces, interface comments

10.1 Interface documentation

The section explains how to document C interfaces with Doxygen-style comments and organize related interfaces in cohesive header files.

• Doxygen interface documentation: Explain why C interfaces should be documented thoroughly and describe how Doxygen-style comments document a function.
  Why it matters: Consistent interface comments make code easier for its users to understand and can be turned into documentation.
• Cohesive interface headers: Explain how grouping related interfaces in a header helps users find the code they need, and describe what the example header contains.
  Why it matters: A cohesive header gives users one place to find the interfaces for a data type.

Key terms: interface, Doxygen, @param, @a, @brief, strong semantic connections, header file, interfaces, include guards

10.2 Implementation

The section explains how clear implementation makes code readable, control flow obvious, and non-obvious ideas worth documenting.

• Readable code and comments: Explain why readable C code may need few comments: names and code structure should make what it does clear, while comments explain ideas and prerequisites that are not obvious.
  Why it matters: Clear code lets readers understand the ordinary steps without relying on comments to narrate them.
• Obvious control flow: Describe how clear grouping and control statements make control flow apparent, and identify buried jumps and hard-to-read controlling expressions as ways to obscure it.
  Why it matters: A reader should be able to follow where execution goes without untangling dense expressions or hidden exits.
• Pure function readability: Explain the property of a pure function stated here and why it helps humans and compilers understand it.
  Why it matters: This explains why a function's limited interaction with the rest of the program can improve readability and implementation efficiency.

Key terms: Implement literally, descriptive text, naming entities, control flow, compound statements, buried jumps, flyspeck expressions, pure functions, interface

10.2.1 Macros

This section explains how to use macros without hiding control flow or making function-like invocations behave unexpectedly.

• Visible macro control flow: Explain why a macro should not hide a return or other surprising control flow, and how an exposed if in its replacement text can cause a dangling else.
  Why it matters: Code that looks straightforward at the call site can behave differently after macro replacement.
• Function call shaped macros: Describe the section's rule that function-like macros should behave syntactically like function calls, including how the do-while(false) wrapper can keep statements together without disrupting surrounding control structures.
  Why it matters: A macro that fits the surrounding syntax is less likely to break otherwise ordinary-looking code.
• Textual replacement pitfalls: Explain the listed syntactic and evaluation hazards of function-like macros: trailing semicolons, commas, expressions that bind unexpectedly, and parameters used more than once.
  Why it matters: Checking the replacement text helps catch behavior that is not apparent from a macro invocation.

Key terms: macros, control flow, dangling else, ERRORCHECK, function-like macros, do-while(false), compound statement, trailing semicolons, comma operators, continuable expressions

10.2.2 Pure functions

This section explains pure, value-based functions and uses rational-number arithmetic to show both their usefulness and their limits.

• Value Parameters and Shared Objects: Explain that C function parameters receive values computed from arguments, so a function does not directly change an argument object through such a parameter. Describe why using a global variable to let functions share an object is discouraged.
  Why it matters: This distinction explains why the section's functions return new values rather than changing their callers' objects.
• Pure Function Properties: Describe the two requirements for a pure function and explain why those requirements give an optimizer flexibility in scheduling its execution.
  Why it matters: Purity makes a small function's effect easy to describe and gives optimizers more freedom.
• Rational Representation and Normalization: Explain why the example's rational numbers need normalization and describe how the product and sum functions use rational representations.
  Why it matters: The example shows how small value-returning functions can work together while maintaining a useful representation.
• Returned Results and Copying: Explain why callers must use the returned value of these pure rational functions, and describe the section's qualified performance concern about copying structures.
  Why it matters: Using the return value is necessary for the example's computations to affect a caller's variable.

Key terms: passed by value, parameters, global variables, pure function, return value, abstract state machine, rat, numerator, denominator, sign

10.2.3 Attributes

This section explains how C23 attributes annotate code for compilers and tools, how to check attribute support, and how to avoid macro interference in headers.

• Unsequenced interface annotations: Explain what [[__unsequenced__]] tells a compiler that sees only a header, and distinguish functions without pointer parameters or returns from those with them.
  Why it matters: An interface annotation can give the compiler useful information even when the function body is unavailable.
• Standard attribute meanings: Describe the purposes of the standard attributes explained here, including how they affect diagnostics or describe a function's behavior.
  Why it matters: These annotations help compilers distinguish intended code from uses worth diagnosing.
• Prefixed implementation attributes: Describe the form and purpose of prefixed attributes, using the format attribute as the section's example.
  Why it matters: Prefixed attributes let implementations supply targeted checks beyond the standard attributes.
• Attribute support testing: Explain how code can conditionally use an attribute when support varies between implementations.
  Why it matters: Checking support avoids unconditionally using an attribute on a platform that may not implement it.
• Macro-safe attribute spelling: Justify the use of double-underscore attribute forms in header files.
  Why it matters: Macro-safe spelling protects a header's annotations from names defined by code that includes it.

Key terms: [[__unsequenced__]], pure, pointer parameters, pointer returns, deprecated, fallthrough, maybe_unused, nodiscard, noreturn, prefixed attributes

10.3 Summary