clang-format Configuration Skill

clang-format Configuration Skill

A comprehensive skill for configuring clang-format to format C/C++/Java/JavaScript/JSON/Objective-C/Protobuf/C# code.

Navigation

Quick Access

• CLI Usage - Command-line tools, flags, and integrations
• Quick Reference - Common patterns and complete examples

Style Options by Category

1. Alignment Options - Align code elements consistently
2. Breaking & Line Wrapping - Control line breaks and wrapping
3. Brace Styles - Configure brace placement and wrapping
4. Indentation - Control indentation behavior
5. Spacing - Fine-tune whitespace placement
6. Include Organization - Sort and organize include directives
7. Language-Specific - Options for specific languages
8. Comments & Misc - Comment formatting and other options
9. Advanced Options - Experimental and advanced features

Complete Reference Documentation

• Full CLI Reference - Complete command-line documentation
• Full Style Options - Complete style configuration reference

What is clang-format?

clang-format is a tool that automatically formats source code according to configurable style rules. It ensures consistent code formatting across your project and team.

Supported Languages:

• C/C++
• Java
• JavaScript/TypeScript
• JSON
• Objective-C
• Protocol Buffers
• C#
• Verilog
• TableGen

Quick Start

1. Create a Configuration File

Generate a .clang-format file based on a predefined style:

clang-format -style=llvm -dump-config > .clang-format

Available Base Styles:

• LLVM - LLVM coding conventions
• Google - Google C++ Style Guide
• GNU - GNU coding style
• Chromium - Chromium project style
• Microsoft - Microsoft coding style
• Mozilla - Mozilla coding style
• WebKit - WebKit coding style

2. Customize Your Configuration

Edit .clang-format to customize specific options:

# Start with a base style
BasedOnStyle: Google

# Customize specific options
IndentWidth: 4
ColumnLimit: 120
PointerAlignment: Left

3. Format Your Code

# Format a single file in-place
clang-format -i src/main.cpp

# Format multiple files
clang-format -i src/*.cpp include/*.h

# Check without modifying (dry run)
clang-format --dry-run src/main.cpp

# Format only changed lines in git
git clang-format

Configuration File Structure

A .clang-format file uses YAML format with key-value pairs:

---
# Language-specific settings
Language: Cpp

# Base style to inherit from
BasedOnStyle: LLVM

# Indentation
IndentWidth: 4
UseTab: Never
TabWidth: 4

# Line length
ColumnLimit: 100

# Braces
BreakBeforeBraces: Allman

# Spacing
SpaceBeforeParens: ControlStatements

# Pointer alignment
PointerAlignment: Left

# Include sorting
SortIncludes: true

Common Workflows

Format on Commit

Format only staged changes before committing:

git clang-format

Format Entire Project

find src include -name '*.cpp' -o -name '*.h' | xargs clang-format -i

Check Formatting in CI

clang-format --dry-run --Werror src/*.cpp include/*.h

Ignore Specific Files

Create .clang-format-ignore:

# Ignore third-party code
third_party/**
external/**

# Ignore generated files
*.pb.cc
*.pb.h

Editor Integration

clang-format integrates with popular editors:

• VS Code: Install "Clang-Format" extension
• CLion: Built-in support (detects .clang-format)
• Vim: Use clang-format.py script
• Emacs: Use clang-format.el

See CLI Usage for detailed integration instructions.

Finding Style Options

Options are organized by category:

• Need to align assignments? → Alignment Options
• Control where lines break? → Breaking & Line Wrapping
• Configure brace placement? → Brace Styles
• Adjust indentation? → Indentation
• Fine-tune spacing? → Spacing
• Organize includes? → Include Organization
• Language-specific needs? → Language-Specific

Example Configurations

See Quick Reference for complete configuration examples:

• Google C++ style customized
• Linux kernel style
• Corporate/Microsoft style
• Modern C++ style

Documentation Structure

This skill is organized into:

1. Navigable sections - Categorized options for easy browsing
2. Complete reference - Full documentation for deep dives
3. Quick reference - Ready-to-use configuration examples

Best Practices

1. Version control your .clang-format file in the repository root
2. Start with a base style that matches your existing conventions
3. Make minimal changes to the base style to reduce maintenance
4. Document deviations from standard styles in comments
5. Test on representative code before applying project-wide
6. Use git integration to format only changed lines
7. Set up editor integration for automatic formatting
8. Create .clang-format-ignore for files that shouldn't be formatted

Troubleshooting

Configuration not found?

• clang-format searches for .clang-format or _clang-format from the source file's directory upward
• Use -style=file:/path/to/.clang-format to specify explicitly

Unknown options warning?

• Use --Wno-error=unknown to allow formatting with unknown (newer) options
• This happens when your config has options not supported by your clang-format version

Want to check effective config?

clang-format -dump-config file.cpp

Next Steps

• Browse Style Options by Category to customize formatting
• Check Quick Reference for complete working examples
• Review CLI Usage for advanced command-line usage
• Consult full reference documentation for comprehensive details