Cpp Quality

C++ Quality Tooling - Quick Reference

Deep Knowledge: Use mcp__documentation__fetch_docs with technology: cpp-quality.

clang-format

Reformats source per a style file. Runs in milliseconds; safe to wire into pre-commit and editors.

.clang-format:

---
BasedOnStyle: LLVM
Language: Cpp
Standard: c++20
ColumnLimit: 100
IndentWidth: 4
AccessModifierOffset: -4
AllowShortFunctionsOnASingleLine: Empty
AlwaysBreakTemplateDeclarations: Yes
BreakBeforeBraces: Attach
NamespaceIndentation: None
PointerAlignment: Left
SortIncludes: CaseInsensitive
IncludeBlocks: Regroup
SpaceAfterTemplateKeyword: false

Run:

clang-format -i src/**/*.cpp include/**/*.hpp
clang-format --dry-run --Werror src/foo.cpp        # CI: fail if not formatted
git ls-files '*.cpp' '*.hpp' | xargs clang-format -i

Choose a base (LLVM, Google, Mozilla, Chromium, Microsoft) and tweak — don't bikeshed style from scratch.

clang-tidy

Linter + simple refactor tool driven by compile_commands.json (enable with set(CMAKE_EXPORT_COMPILE_COMMANDS ON)).

.clang-tidy:

---
Checks: >
  -*,
  bugprone-*,
  cert-*,
  clang-analyzer-*,
  concurrency-*,
  cppcoreguidelines-*,
  modernize-*,
  performance-*,
  portability-*,
  readability-*,
  -modernize-use-trailing-return-type,
  -readability-magic-numbers,
  -readability-identifier-length,
  -cppcoreguidelines-avoid-magic-numbers
WarningsAsErrors: '*'
HeaderFilterRegex: '^.*/(include|src)/.*\.(h|hpp)$'
FormatStyle: file
CheckOptions:
  - { key: readability-function-cognitive-complexity.Threshold, value: '25' }
  - { key: cppcoreguidelines-avoid-non-const-global-variables.AllowInternalLinkage, value: 'true' }

Run:

# Single file
clang-tidy -p build src/foo.cpp

# Whole project (parallelized)
run-clang-tidy -p build -quiet -header-filter='^.*/(include|src)/.*'

# Auto-apply fixes
run-clang-tidy -p build -fix -fix-errors

# CMake target
add_custom_target(tidy COMMAND run-clang-tidy -p ${CMAKE_BINARY_DIR})

High-value check categories

Suppressing

// One line
int* p = (int*)x;  // NOLINT(cppcoreguidelines-pro-type-cstyle-cast)

// Block
// NOLINTBEGIN(modernize-use-nodiscard)
int legacy_api();
// NOLINTEND(modernize-use-nodiscard)

Prefer fixing or disabling at config level for whole categories you don't want.

cppcheck (complementary, not a replacement)

cppcheck --enable=warning,style,performance,portability \
         --inline-suppr --error-exitcode=2 \
         --project=build/compile_commands.json \
         --suppress=missingIncludeSystem \
         -i tests

Catches different patterns than clang-tidy (less path-sensitive but quicker; flags some uninitialized-member and dangling-reference issues clang-tidy misses).

include-what-you-use (IWYU)

Reduces include bloat → faster builds + fewer accidental dependencies.

iwyu_tool.py -p build src/foo.cpp
fix_includes.py < iwyu.out                # auto-apply suggestions

Annotate to override:

#include <vector>          // IWYU pragma: keep
class Foo;                 // IWYU pragma: forward_declare

Compiler warnings (the cheap layer underneath)

target_compile_options(mylib PRIVATE
    $<$<CXX_COMPILER_ID:MSVC>:/W4 /WX /permissive- /w14640>
    $<$<NOT:$<CXX_COMPILER_ID:MSVC>>:
        -Wall -Wextra -Wpedantic -Werror
        -Wshadow -Wnon-virtual-dtor -Wold-style-cast
        -Wcast-align -Woverloaded-virtual -Wconversion -Wsign-conversion
        -Wnull-dereference -Wdouble-promotion -Wformat=2
    >
)

Don't skip this in favor of clang-tidy — compiler warnings are free and faster than any external tool.

CI pipeline (GitHub Actions sketch)

- name: Configure
  run: cmake --preset debug

- name: Format check
  run: |
    git ls-files '*.cpp' '*.hpp' | xargs clang-format --dry-run --Werror

- name: Build
  run: cmake --build --preset debug -j

- name: clang-tidy
  run: run-clang-tidy -p build/debug -quiet

- name: Test
  run: ctest --preset debug

Anti-Patterns