# Cpp

> Google's official C++ style guide. Covers headers, naming conventions, formatting, classes, memory management, RAII, smart pointers, and modern C++ features.

- Skill: `testdino-hq/cpp` (Agent Skill, multi-file: 2 files)
- Install (CLI): `npx skillmds@latest add testdino-hq/cpp`
- Raw SKILL.md: https://api.skillmd.com/api/skills/testdino-hq/cpp/raw
- Safety review: pending
- Works with: Claude Code, Claude.ai, OpenAI Codex
- Category: Coding & Dev Tools
- Author: testdino-hq (https://skillmd.com/u/testdino-hq)
- Updated: 2026-09-17
- Page: https://skillmd.com/skills/testdino-hq/cpp

---


# Google C++ Style Guide

> Official Google C++ coding standards for consistent, maintainable code.

## Golden Rules

1. **Target C++20** — avoid non-standard extensions
2. **80-character line limit** — for readability
3. **2-space indentation** — no tabs
4. **Use `const` liberally** — for correctness and thread safety
5. **Avoid exceptions** — Google code doesn't use C++ exceptions
6. **Smart pointers for ownership** — `std::unique_ptr` and `std::shared_ptr`
7. **Header guards** — use `PROJECT_PATH_FILE_H_` format

## Quick Reference

### Naming Conventions

| Element | Convention | Example |
|---|---|---|
| Files | snake_case | `url_table.cc`, `url_table.h` |
| Classes/Structs | UpperCamelCase | `UserService` |
| Functions | UpperCamelCase | `GetUserById` |
| Variables | snake_case | `user_count` |
| Constants | kUpperCamelCase | `kMaxRetries` |
| Class members | snake_case_ | `user_name_` (trailing `_`) |
| Macros | UPPER_SNAKE_CASE | `MAX_BUFFER_SIZE` |

### Headers

```cpp
// ✓ CORRECT - self-contained header with guard
#ifndef FOO_BAR_BAZ_H_
#define FOO_BAR_BAZ_H_

#include <string>
#include "base/basictypes.h"

class Baz {
 public:
  void DoSomething();
};

#endif  // FOO_BAR_BAZ_H_
```

Include order: related header → C system → C++ stdlib → other libs → your headers.

### Classes

```cpp
// ✓ CORRECT
class MyClass {
 public:
  explicit MyClass(int value);  // explicit for single-arg ctors
  ~MyClass();

  void DoSomething();
  int GetValue() const { return value_; }

 private:
  int value_;
  std::string name_;
};
```

### Smart Pointers

```cpp
// ✓ CORRECT - unique_ptr for exclusive ownership
std::unique_ptr<Foo> FooFactory();
void FooConsumer(std::unique_ptr<Foo> ptr);

// ✓ CORRECT - shared_ptr for shared ownership
std::shared_ptr<const Foo> immutable_foo;

// ✗ INCORRECT - avoid raw new/delete
Foo* foo = new Foo();  // avoid
delete foo;            // avoid
```

### Modern C++ Features

```cpp
// ✓ CORRECT - use auto for complex types
auto it = my_map.find(key);
auto widget = std::make_unique<Widget>(arg1, arg2);

// ✓ CORRECT - range-based for loops
for (const auto& item : container) {
  Process(item);
}

// ✓ CORRECT - nullptr, not NULL
Foo* ptr = nullptr;

// ✓ CORRECT - constexpr for compile-time constants
constexpr int kArraySize = 100;
```

### Functions

```cpp
// ✓ CORRECT - return type on same line
ReturnType ClassName::FunctionName(Type par_name1, Type par_name2) {
  DoSomething();
  return result;
}

// ✓ CORRECT - wrap long parameter lists (4-space indent)
ReturnType LongClassName::ReallyLongFunctionName(
    Type par_name1,
    Type par_name2,
    Type par_name3) {
  DoSomething();
}
```

### Formatting

```cpp
// ✓ CORRECT - braces and spacing
if (condition) {
  DoSomething();
} else {
  DoSomethingElse();
}

// ✓ CORRECT - pointer/reference alignment (attached to type)
char* c;
const std::string& str;
```

## Common Mistakes

| Mistake | Correct Approach |
|---|---|
| Using exceptions | Use error codes or `absl::Status` |
| Bare `new`/`delete` | Use smart pointers (`unique_ptr`) |
| `NULL` or `0` for null | Use `nullptr` |
| C-style casts | Use C++ casts (`static_cast`, etc.) |
| `using namespace std` | Never in headers; avoid in `.cc` |
| Mutable global variables | Use singletons or dependency injection |
| Missing `explicit` | Mark single-arg constructors `explicit` |

## When to Use This Guide

- Writing new C++ code
- Refactoring existing C++
- Code reviews
- Setting up clang-format rules
- Onboarding new team members

## Install

```bash
npx skills add testdino-hq/google-styleguides-skills/cpp
```

## Full Guide

See [cpp.md](cpp.md) for complete details, examples, and edge cases.