Cpp Coding Standards

C++ Coding Standards (C++ Core Guidelines)

Comprehensive coding standards for modern C++ (C++17/20/23) derived from the C++ Core Guidelines. Enforces type safety, resource safety, immutability, and clarity.

When to Use

• Writing new C++ code (classes, functions, templates)
• Reviewing or refactoring existing C++ code
• Making architectural decisions in C++ projects
• Enforcing consistent style across a C++ codebase
• Choosing between language features (e.g., enum vs enum class, raw pointer vs smart pointer)

When NOT to Use

• Non-C++ projects
• Legacy C codebases that cannot adopt modern C++ features
• Embedded/bare-metal contexts where specific guidelines conflict with hardware constraints (adapt selectively)

Cross-Cutting Principles

These themes recur across the entire guidelines and form the foundation:

1. RAII everywhere (P.8, R.1, E.6, CP.20): Bind resource lifetime to object lifetime
2. Immutability by default (P.10, Con.1-5, ES.25): Start with const/constexpr; mutability is the exception
3. Type safety (P.4, I.4, ES.46-49, Enum.3): Use the type system to prevent errors at compile time
4. Express intent (P.3, F.1, NL.1-2, T.10): Names, types, and concepts should communicate purpose
5. Minimize complexity (F.2-3, ES.5, Per.4-5): Simple code is correct code
6. Value semantics over pointer semantics (C.10, R.3-5, F.20, CP.31): Prefer returning by value and scoped objects

Philosophy & Interfaces (P., I.)

Key Rules

DO

// P.10 + I.4: Immutable, strongly typed interface
struct Temperature {
    double kelvin;
};

Temperature boil(const Temperature& water);

DON'T

// Weak interface: unclear ownership, unclear units
double boil(double* temp);

// Non-const global variable
int g_counter = 0;  // I.2 violation

Functions (F.*)

Key Rules

Parameter Passing

// F.16: Cheap types by value, others by const&
void print(int x);                           // cheap: by value
void analyze(const std::string& data);       // expensive: by const&
void transform(std::string s);               // sink: by value (will move)

// F.20 + F.21: Return values, not output parameters
struct ParseResult {
    std::string token;
    int position;
};

ParseResult parse(std::string_view input);   // GOOD: return struct

// BAD: output parameters
void parse(std::string_view input,
           std::string& token, int& pos);    // avoid this

Pure Functions and constexpr

// F.4 + F.8: Pure, constexpr where possible
constexpr int factorial(int n) noexcept {
    return (n <= 1) ? 1 : n * factorial(n - 1);
}

static_assert(factorial(5) == 120);

Anti-Patterns

• Returning T&& from functions (F.45)
• Using va_arg / C-style variadics (F.55)
• Capturing by reference in lambdas passed to other threads (F.53)
• Returning const T which inhibits move semantics (F.49)

Classes & Class Hierarchies (C.*)

Key Rules

Rule of Zero

// C.20: Let the compiler generate special members
struct Employee {
    std::string name;
    std::string department;
    int id;
    // No destructor, copy/move constructors, or assignment operators needed
};

Rule of Five

// C.21: If you must manage a resource, define all five
class Buffer {
public:
    explicit Buffer(std::size_t size)
        : data_(std::make_unique<char[]>(size)), size_(size) {}

    ~Buffer() = default;

    Buffer(const Buffer& other)
        : data_(std::make_unique<char[]>(other.size_)), size_(other.size_) {
        std::copy_n(other.data_.get(), size_, data_.get());
    }

    Buffer& operator=(const Buffer& other) {
        if (this != &other) {
            auto new_data = std::make_unique<char[]>(other.size_);
            std::copy_n(other.data_.get(), other.size_, new_data.get());
            data_ = std::move(new_data);
            size_ = other.size_;
        }
        return *this;
    }

    Buffer(Buffer&&) noexcept = default;
    Buffer& operator=(Buffer&&) noexcept = default;

private:
    std::unique_ptr<char[]> data_;
    std::size_t size_;
};

Class Hierarchy

// C.35 + C.128: Virtual destructor, use override
class Shape {
public:
    virtual ~Shape() = default;
    virtual double area() const = 0;  // C.121: pure interface
};

class Circle : public Shape {
public:
    explicit Circle(double r) : radius_(r) {}
    double area() const override { return 3.14159 * radius_ * radius_; }

private:
    double radius_;
};

Anti-Patterns

• Calling virtual functions in constructors/destructors (C.82)
• Using memset/memcpy on non-trivial types (C.90)
• Providing different default arguments for virtual function and overrider (C.140)
• Making data members const or references, which suppresses move/copy (C.12)

Resource Management (R.*)

Key Rules

Smart Pointer Usage

// R.11 + R.20 + R.21: RAII with smart pointers
auto widget = std::make_unique<Widget>("config");  // unique ownership
auto cache  = std::make_shared<Cache>(1024);        // shared ownership

// R.3: Raw pointer = non-owning observer
void render(const Widget* w) {  // does NOT own w
    if (w) w->draw();
}

render(widget.get());

RAII Pattern

// R.1: Resource acquisition is initialization
class FileHandle {
public: