概述

C++11引入了一系列改进和新特性，旨在提升语言的性能、易用性和安全性。这些新特性包括模板元编程的增强、自动类型推断、范围基于的for循环、可变参数模板、并行编程支持等。本文将详细介绍C++11中的可变参数模板、通用迭代器、constexpr函数等新特性，并以示例代码指导如何在实践案例中应用这些特性。

C++11特性介绍与实践

可变参数模板示例

#include <iostream>

template <typename... Args>
void log(const char* format, Args... args) {
    std::cout << std::vsnprintf(nullptr, 0, format, std::make_tuple(args...)) << std::endl;
}

int main() {
    log("Hello, World!");
    log("The sum of %d and %d is %d", 1, 2, 3);
    return 0;
}

使用std::optional处理空值

#include <optional>

void process() {
    auto result = std::optional<std::string>{"Hello"};
    if (result) {
        std::cout << *result << std::endl;
    } else {
        std::cout << "No result" << std::endl;
    }
}

使用std::move优化函数调用

#include <functional>

void exchange(int& a, int& b) {
    std::swap(a, b);
}

int main() {
    int x = 5, y = 10;
    exchange(x, y); // 使用std::move提高性能
    std::cout << "x = " << x << ", y = " << y << std::endl;
    return 0;
}

使用范围for循环遍历容器

#include <iostream>
#include <vector>

int main() {
    std::vector<int> numbers = {1, 2, 3, 4, 5};
    for (int num : numbers) {
        std::cout << num << " ";
    }
    std::cout << std::endl;
    return 0;
}

使用constexpr进行计算

#include <iostream>

constexpr int add(int a, int b) {
    return a + b;
}

int main() {
    std::cout << "The sum is: " << add(10, 20) << std::endl;
    return 0;
}

使用std::optional和std::array

#include <optional>
#include <array>

int main() {
    std::array<int, 3> data = {1, 2, 3};
    std::optional<std::array<int, 3>> optData = data;
    if (optData) {
        for (int val : *optData) {
            std::cout << val << " ";
        }
    }
    return 0;
}

使用std::find_if和std::reverse

#include <iostream>
#include <vector>
#include <algorithm>

int main() {
    std::vector<int> numbers = {3, 2, 1, 4, 5};
    auto it = std::find_if(numbers.begin(), numbers.end(), [](int n) { return n > 2; });
    if (it != numbers.end()) {
        std::cout << *it << " is the first number greater than 2." << std::endl;
    } else {
        std::cout << "No number greater than 2 found." << std::endl;
    }
    std::reverse(numbers.begin(), numbers.end());
    for (int n : numbers) {
        std::cout << n << " ";
    }
    std::cout << std::endl;
    return 0;
}

并发与线程支持的示例

使用std::atomic和std::mutex

#include <iostream>
#include <thread>
#include <atomic>
#include <mutex>

std::atomic<int> counter(0);
std::mutex mtx;

void incrementCounter() {
    std::lock_guard<std::mutex> lock(mtx);
    ++counter;
    std::cout << "Counter incremented to " << counter << std::endl;
}

int main() {
    std::thread t1(incrementCounter);
    std::thread t2(incrementCounter);
    t1.join();
    t2.join();
    return 0;
}

使用std::async进行并发计算

#include <iostream>
#include <future>

std::future<int> asyncCompute() {
    std::promise<int> promise;
    std::future<int> future = promise.get_future();
    std::thread t([]() {
        int result = 100;
        promise.set_value(result);
    });
    t.join();
    return future;
}

int main() {
    int result = asyncCompute().get();
    std::cout << "Result: " << result << std::endl;
    return 0;
}

实践案例与代码示例

使用std::make_unique进行内存管理

#include <iostream>
#include <memory>

struct MyClass {
    MyClass() { std::cout << "Created" << std::endl; }
    ~MyClass() { std::cout << "Destroyed" << std::endl; }
};

int main() {
    std::unique_ptr<MyClass> ptr = std::make_unique<MyClass>();
    ptr->MyClass::MyClass(); // Created
    // 使用完毕后自动调用析构函数
    return 0;
}

具体并发场景下的线程池应用

#include <iostream>
#include <thread>
#include <vector>
#include <future>
#include <mutex>
#include <condition_variable>

std::mutex mtx;
std::condition_variable cv;
int counter = 0;

void incrementCounter(int n) {
    std::unique_lock<std::mutex> lock(mtx);
    for (int i = 0; i < n; ++i) {
        ++counter;
    }
    cv.notify_one();
}

int main() {
    std::vector<std::future<void>> futures;
    const int nThreads = 10;
    const int nIncrement = 10000000;

    for (int i = 0; i < nThreads; ++i) {
        futures.push_back(std::async(std::launch::async, incrementCounter, nIncrement));
    }

    for (auto& future : futures) {
        future.wait();
    }

    std::cout << "Final counter value: " << counter << std::endl;
    return 0;
}

本文通过全面介绍了C++11的关键特性及其在实际编程中的应用方法，为学习者提供了从基础到实践的快速入门指南。C++11的引入为C++语言带来了许多重要的改进，使得编写更安全、更高效和更易于维护的代码成为可能。