---
id: miles990/claude-software-skills/cpp
version: "eb1c6089"
license: MIT
install: manual
updated: 2026-01-20
---

# cpp — This skill covers contemporary C++ practices from C++11 onward, emphasizing memory safety through smart pointers (unique_ptr, shared_ptr, weak_ptr) and the RAII pattern for automatic resource cleanup. You'll explore move semantics and perfect forwarding to optimize performance, dive into function and class templates with specialization techniques, and learn STL containers and algorithms for efficient data manipulation.

Publisher: miles990 · Stars: 19 · Updated: 2026-01-20

Install (manual): `git clone https://github.com/miles990/claude-software-skills`

## SKILL.md

# C++

## Overview

Modern C++ (C++11 and beyond) patterns including RAII, smart pointers, templates, and STL.

---

## Modern C++ Fundamentals

### Smart Pointers

```cpp
#include <memory>
#include <iostream>

// unique_ptr - exclusive ownership
class Resource {
public:
    Resource() { std::cout << "Resource acquired\n"; }
    ~Resource() { std::cout << "Resource released\n"; }
    void use() { std::cout << "Resource used\n"; }
};

void unique_ptr_example() {
    // Create unique_ptr
    auto ptr = std::make_unique<Resource>();
    ptr->use();

    // Transfer ownership
    auto ptr2 = std::move(ptr);
    // ptr is now nullptr

    // Array support
    auto arr = std::make_unique<int[]>(10);
}

// shared_ptr - shared ownership
void shared_ptr_example() {
    auto shared1 = std::make_shared<Resource>();
    {
        auto shared2 = shared1; // Reference count = 2
        shared2->use();
    } // shared2 destroyed, count = 1

    std::cout << "Use count: " << shared1.use_count() << "\n";
} // shared1 destroyed, resource released

// weak_ptr - non-owning reference
class Node {
public:
    std::shared_ptr<Node> next;
    std::weak_ptr<Node> prev; // Avoid circular reference

    ~Node() { std::cout << "Node destroyed\n"; }
};

void weak_ptr_example() {
    auto node1 = std::make_shared<Node>();
    auto node2 = std::make_shared<Node>();

    node1->next = node2;
    node2->prev = node1; // weak_ptr, no ownership

    if (auto locked = node2->prev.lock()) {
        // Use locked (shared_ptr)
    }
}
```

### RAII Pattern

```cpp
#include <fstream>
#include <mutex>

// File wrapper with RAII
class File {
    std::fstream file_;

public:
    explicit File(const std::string& filename)
        : file_(filename, std::ios::in | std::ios::out) {
        if (!file_.is_open()) {
            throw std::runtime_error("Failed to open file");
        }
    }

    ~File() {
        if (file_.is_open()) {
            file_.close();
        }
    }

    // Delete copy operations
    File(const File&) = delete;
    File& operator=(const File&) = delete;

    // Allow move operations
    File(File&& other) noexcept : file_(std::move(other.file_)) {}
    File& operator=(File&& other) noexcept {
        file_ = std::move(other.file_);
        return *this;
    }

    void write(const std::string& data) {
        file_ << data;
    }
};

// Lock guard (RAII for mutex)
class ThreadSafeCounter {
    mutable std::mutex mutex_;
    int count_ = 0;

public:
    void increment() {
        std::lock_guard<std::mutex> lock(mutex_);
        ++count_;
    }

    int get() const {
        std::lock_guard<std::mutex> lock(mutex_);
        return count_;
    }
};

// Scoped cleanup
template<typename F>
class ScopeGuard {
    F cleanup_;
    bool active_ = true;

public:
    explicit ScopeGuard(F cleanup) : cleanup_(std::move(cleanup)) {}

    ~ScopeGuard() {
        if (active_) cleanup_();
    }

    void dismiss() { active_ = false; }

    ScopeGuard(const ScopeGuard&) = delete;
    ScopeGuard& operator=(const ScopeGuard&) = delete;
};

// Usage
void example() {
    auto resource = acquireResource();
    ScopeGuard guard([&]() { releaseResource(resource); });

    // Do work...

    guard.dismiss(); // Don't cleanup if successful
}
```

### Move Semantics

```cpp
#include <vector>
#include <string>
#include <utility>

class Buffer {
    std::unique_ptr<char[]> data_;
    size_t size_;

public:
    // Constructor
    explicit Buffer(size_t size) : data_(new char[size]), size_(size) {}

    // Copy constructor
    Buffer(const Buffer& other) : data_(new char[other.size_]), size_(other.size_) {
        std::copy(other.data_.get(), other.data_.get() + size_, data_.get());
    }

    // Move constructor
    Buffer(Buffer&& other) noexcept
        : data_(std::move(other.data_)), size_(other.size_) {
        other.size_ = 0;
    }

    // Copy assignment
    Buffer& operator=(const Buffer& other) {
        if (this != &other) {
            data_.reset(new char[other.size_]);
            size_ = other.size_;
            std::copy(other.data_.get(), other.data_.get() + size_, data_.get());
        }
        return *this;
    }

    // Move assignment
    Buffer& operator=(Buffer&& other) noexcept {
        if (this != &other) {
            data_ = std::move(other.data_);
            size_ = other.size_;
            other.size_ = 0;
        }
        return *this;
    }

    size_t size() const { return size_; }
};

// Perfect forwarding
template<typename T, typename... Args>
std::unique_ptr<T> make_unique_custom(Args&&... args) {
    return std::unique_ptr<T>(new T(std::forward<Args>(args)...));
}
```

---

## Templates

### Function Templates

```cpp
#include <type_traits>
#include <concepts>

// Basic template
template<typename T>
T max(T a, T b) {
    return (a > b) ? a : b;
}

// Template specialization
template<>
const char* max<const char*>(const char* a, const char* b) {
    return (strcmp(a, b) > 0) ? a : b;
}

// SFINAE (Substitution Failure Is Not An Error)
template<typename T>
typename std::enable_if<std::is_integral<T>::value, T>::type
double_value(T value) {
    return value * 2;
}

// C++20 Concepts
template<typename T>
concept Numeric = std::is_arithmetic_v<T>;

template<Numeric T>
T add(T a, T b) {
    return a + b;
}

// Requires clause
template<typename T>
requires std::is_default_constructible_v<T>
T create_default() {
    return T{};
}

// Variadic templates
template<typename... Args>
void print(Args... args) {
    (std::cout << ... << args) << "\n";
}

// Fold expressions
template<typename... Args>
auto sum(Args... args) {
    return (args + ...);
}
```

### Class Templates

```cpp
// Generic container
template<typename T, size_t N>
class Array {
    T data_[N];

public:
    constexpr size_t size() const { return N; }

    T& operator[](size_t index) {
        if (index >= N) throw std::out_of_range("Index out of range");
        return data_[index];
    }

    const T& operator[](size_t index) const {
        if (index >= N) throw std::out_of_range("Index out of range");
        return data_[index];
    }

    T* begin() { return data_; }
    T* end() { return data_ + N; }
    const T* begin() const { return data_; }
    const T* end() const { return data_ + N; }
};

// Template with default arguments
template<typename T, typename Allocator = std::allocator<T>>
class Vector {
    // ...
};

// Partial specialization
template<typename T>
class Container<T*> {
    // Specialization for pointer types
};

// CRTP (Curiously Recurring Template Pattern)
template<typename Derived>
class Counter {
    static inline int count_ = 0;

public:
    Counter() { ++count_; }
    ~Counter() { --count_; }

    static int count() { return count_; }
};

class Widget : public Counter<Widget> {
    // Widget inherits counting behavior
};
```

---

## STL Containers and Algorithms

```cpp
#include <vector>
#include <map>
#include <unordered_map>
#include <set>
#include <algorithm>
#include <numeric>

void container_examples() {
    // vector
    std::vector<int> vec{1, 2, 3, 4, 5};
    vec.push_back(6);
    vec.emplace_back(7); // Construct in place

    // map
    std::map<std::string, int> ordered_map;
    ordered_map["one"] = 1;
    ordered_map.insert({"two", 2});
    ordered_map.try_emplace("three", 3);

    // unordered_map
    std::unordered_map<std::string, int> hash_map;
    hash_map["one"] = 1;

    // set
    std::set<int> ordered_set{3, 1, 4, 1, 5};
    auto [iter, inserted] = ordered_set.insert(9);
}

void algorithm_examples() {
    std::vector<int> vec{5, 2, 8, 1, 9, 3};

    // Sort
    std::sort(vec.begin(), vec.end());
    std::sort(vec.begin(), vec.end(), std::greater<int>());

    // Find
    auto it = std::find(vec.begin(), vec.end(), 8);
    auto it2 = std::find_if(vec.begin(), vec.end(), [](int n) { return n > 5; });

    // Transform
    std::vector<int> doubled(vec.size());
    std::transform(vec.begin(), vec.end(), doubled.begin(), [](int n) { return n * 2; });

    // Accumulate
    int sum = std::accumulate(vec.begin(), vec.end(), 0);

    // Remove-erase idiom
    vec.erase(std::remove_if(vec.begin(), vec.end(), [](int n) { return n < 3; }), vec.end());

    // C++20 ranges (simplified)
    // auto result = vec | std::views::filter([](int n) { return n > 3; })
    //                   | std::views::transform([](int n) { return n * 2; });
}
```

---

## Concurrency

```cpp
#include <thread>
#include <future>
#include <mutex>
#include <condition_variable>
#include <atomic>

// Basic threading
void thread_example() {
    std::thread t([]() {
        std::cout << "Hello from thread\n";
    });
    t.join();
}

// async/future
std::future<int> async_example() {
    return std::async(std::launch::async, []() {
        std::this_thread::sleep_for(std::chrono::seconds(1));
        return 42;
    });
}

// promise/future
void promise_example() {
    std::promise<int> promise;
    std::future<int> future = promise.get_future();

    std::thread producer([&promise]() {
        promise.set_value(42);
    });

    int result = future.get();
    producer.join();
}

// Thread-safe queue
template<typename T>
class ThreadSafeQueue {
    std::queue<T> queue_;
    mutable std::mutex mutex_;
    std::condition_variable cond_;

public:
    void push(T value) {
        std::lock_guard<std::mutex> lock(mutex_);
        queue_.push(std::move(value));
        cond_.notify_one();
    }

    T pop() {
        std::unique_lock<std::mutex> lock(mutex_);
        cond_.wait(lock, [this]() { return !queue_.empty(); });
        T value = std::move(queue_.front());
        queue_.pop();
        return value;
    }

    bool try_pop(T& value) {
        std::lock_guard<std::mutex> lock(mutex_);
        if (queue_.empty()) return false;
        value = std::move(queue_.front());
        queue_.pop();
        return true;
    }
};

// Atomic operations
class AtomicCounter {
    std::atomic<int> count_{0};

public:
    void increment() { count_.fetch_add(1, std::memory_order_relaxed); }
    int get() const { return count_.load(std::memory_order_relaxed); }
};
```

---

## Lambda Expressions

```cpp
#include <functional>

void lambda_examples() {
    // Basic lambda
    auto add = [](int a, int b) { return a + b; };

    // Capture by value
    int x = 10;
    auto by_value = [x]() { return x; };

    // Capture by reference
    auto by_ref = [&x]() { x++; };

    // Capture all by value
    auto all_value = [=]() { return x; };

    // Capture all by reference
    auto all_ref = [&]() { x++; };

    // Mutable lambda (modify captured values)
    auto mutable_lambda = [x]() mutable { return ++x; };

    // Generic lambda (C++14)
    auto generic = [](auto a, auto b) { return a + b; };

    // Init capture (C++14)
    auto ptr = std::make_unique<int>(42);
    auto capture_move = [p = std::move(ptr)]() { return *p; };

    // Template lambda (C++20)
    auto template_lambda = []<typename T>(std::vector<T>& vec) {
        return vec.size();
    };

    // Constexpr lambda (C++17)
    constexpr auto square = [](int n) constexpr { return n * n; };
    static_assert(square(5) == 25);
}

// Storing lambdas
class EventHandler {
    std::function<void(int)> handler_;

public:
    void set_handler(std::function<void(int)> handler) {
        handler_ = std::move(handler);
    }

    void trigger(int value) {
        if (handler_) handler_(value);
    }
};
```

---

## Error Handling

```cpp
#include <stdexcept>
#include <optional>
#include <variant>
#include <expected> // C++23

// Custom exception
class DatabaseError : public std::runtime_error {
    int error_code_;

public:
    DatabaseError(const std::string& message, int code)
        : std::runtime_error(message), error_code_(code) {}

    int error_code() const { return error_code_; }
};

// std::optional for nullable values
std::optional<int> find_value(const std::string& key) {
    if (key == "answer") return 42;
    return std::nullopt;
}

void optional_usage() {
    auto result = find_value("answer");

    if (result) {
        std::cout << "Found: " << *result << "\n";
    }

    int value = result.value_or(0);
}

// std::variant for type-safe union
using Result = std::variant<int, std::string>;

Result compute(bool success) {
    if (success) return 42;
    return std::string("error");
}

void variant_usage() {
    Result r = compute(true);

    std::visit([](auto&& arg) {
        using T = std::decay_t<decltype(arg)>;
        if constexpr (std::is_same_v<T, int>) {
            std::cout << "Success: " << arg << "\n";
        } else {
            std::cout << "Error: " << arg << "\n";
        }
    }, r);
}

// std::expected (C++23)
// std::expected<int, std::string> divide(int a, int b) {
//     if (b == 0) return std::unexpected("Division by zero");
//     return a / b;
// }
```

---

## Related Skills

- [[system-design]] - Systems programming
- [[performance-optimization]] - Low-level optimization
- [[desktop-apps]] - Native applications


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