基于C++协程和事件循环的网络库
以下是基于C++协程和事件循环的网络库实例，涵盖常见场景和功能实现。示例基于libuv、Boost.Asio或自定义事件循环，结合C++20协程（如std::coroutine）或其他协程库（如cppcoro）实现。
基础TCP服务器
#include <cppcoro/task.hpp>
#include <cppcoro/io_service.hpp>
#include <cppcoro/socket.hpp>cppcoro::task<> handle_connection(cppcoro::socket client) {char buffer[1024];auto bytes_read = co_await client.recv(buffer, sizeof(buffer));co_await client.send(buffer, bytes_read);client.close();
}cppcoro::task<> tcp_server(cppcoro::io_service& io_service, uint16_t port) {auto listen_socket = cppcoro::socket::create_tcpv4(io_service);listen_socket.bind(cppcoro::ipv4_endpoint{ {}, port });listen_socket.listen();while (true) {auto client = co_await listen_socket.accept();handle_connection(std::move(client));}
}
异步HTTP客户端
#include <cppcoro/http/client.hpp>cppcoro::task<> fetch_data() {cppcoro::http::client client;auto response = co_await client.request("GET", "https://example.com");std::string body = co_await response.body();std::cout << "Response: " << body << std::endl;
}
定时器任务
#include <cppcoro/task.hpp>
#include <cppcoro/io_service.hpp>
#include <cppcoro/sync_wait.hpp>cppcoro::task<> delayed_task(cppcoro::io_service& io_service) {co_await io_service.schedule_after(std::chrono::seconds(1));std::cout << "Task executed after 1 second" << std::endl;
}
文件异步读取
#include <cppcoro/io_service.hpp>
#include <cppcoro/read_only_file.hpp>cppcoro::task<> read_file(cppcoro::io_service& io_service) {auto file = cppcoro::read_only_file::open(io_service, "example.txt");char buffer[1024];auto bytes_read = co_await file.read(0, buffer, sizeof(buffer));std::cout << "File content: " << std::string(buffer, bytes_read) << std::endl;
}
UDP广播服务器
#include <cppcoro/socket.hpp>cppcoro::task<> udp_broadcaster(cppcoro::io_service& io_service) {auto socket = cppcoro::socket::create_udpv4(io_service);socket.bind(cppcoro::ipv4_endpoint{ {}, 12345 });const char* message = "Broadcast message";co_await socket.send_to(cppcoro::ipv4_endpoint{ INADDR_BROADCAST, 12345 }, message, strlen(message));
}
协程并行任务
#include <cppcoro/when_all.hpp>cppcoro::task<int> task1() { co_return 42; }
cppcoro::task<std::string> task2() { co_return "hello"; }cppcoro::task<> run_parallel() {auto [num, str] = co_await cppcoro::when_all(task1(), task2());std::cout << num << ", " << str << std::endl;
}
WebSocket服务器
#include <boost/beast/core.hpp>
#include <boost/beast/websocket.hpp>boost::asio::awaitable<void> ws_session(boost::beast::websocket::stream<boost::beast::tcp_stream> ws) {co_await ws.async_accept();while (true) {boost::beast::flat_buffer buffer;co_await ws.async_read(buffer);co_await ws.async_write(buffer.data());}
}
SSL/TLS加密连接
#include <boost/asio/ssl.hpp>boost::asio::awaitable<void> ssl_client(boost::asio::ssl::stream<boost::asio::ip::tcp::socket> ssl_socket) {co_await ssl_socket.async_handshake(boost::asio::ssl::stream_base::client);co_await ssl_socket.async_write_some(boost::asio::buffer("Hello SSL"));
}
协程任务取消
#include <cppcoro/cancellation_token.hpp>cppcoro::task<> cancellable_task(cppcoro::cancellation_token token) {while (!token.is_cancellation_requested()) {co_await std::chrono::seconds(1);std::cout << "Working..." << std::endl;}std::cout << "Cancelled!" << std::endl;
}
异步DNS解析
#include <cppcoro/net/ip_address.hpp>cppcoro::task<> resolve_hostname(cppcoro::io_service& io_service) {auto addresses = co_await cppcoro::dns::resolve(io_service, "example.com");for (const auto& addr : addresses) {std::cout << "Resolved IP: " << addr.to_string() << std::endl;}
}
基于C++ auto关键字的实例
以下是基于C++ auto关键字的实用示例，涵盖不同场景下的应用，包括容器遍历、Lambda表达式、类型推导等。示例均遵循现代C++（C++11及以上）标准编写。
基础类型推导
auto x = 42; // 推导为int
auto y = 3.14; // 推导为double
auto z = "Hello"; // 推导为const char*
auto flag = true; // 推导为bool
容器遍历
std::vector<int> vec = {1, 2, 3};
for (auto num : vec) { // 自动推导为intstd::cout << num << " ";
}
STL迭代器简化
std::map<std::string, int> m = {{"a", 1}, {"b", 2}};
for (auto it = m.begin(); it != m.end(); ++it) {std::cout << it->first << ": " << it->second << "\n";
}
Lambda表达式
auto add = [](auto a, auto b) { return a + b; }; // C++14泛型Lambda
std::cout << add(5, 3.2); // 输出8.2
函数返回类型推导（C++14）
auto multiply(double a, double b) {return a * b; // 返回类型推导为double
}
结构化绑定（C++17）
std::tuple<int, std::string> t = {1, "Alice"};
auto [id, name] = t; // 自动解包
模板函数简化
template<typename T>
auto process(T container) -> decltype(container.size()) {return container.size();
}
类型别名简化
auto ptr = std::make_shared<int>(10); // 推导为std::shared_ptr<int>
避免冗长的类型声明
std::vector<std::map<std::string, std::list<int>>> complex;
for (auto& outer : complex) { // 避免重复复杂类型for (auto& inner : outer) {for (auto num : inner.second) {/* ... */}}
}
类型安全的NULL指针
auto nullPtr = nullptr; // 推导为std::nullptr_t
范围循环与引用
std::vector<std::string> names = {"Bob", "Eve"};
for (auto& name : names) { // 避免拷贝name += "!";
}
函数指针简化
auto funcPtr = &multiply; // 推导为double(*)(double, double)
类型推导与const
const auto pi = 3.14159; // 推导为const double
auto& ref = pi; // 推导为const double&
初始化列表
auto list = {1, 2, 3}; // 推导为std::initializer_list<int>
类型萃取辅助
std::vector<int> v = {1, 2, 3};
auto size = v.size(); // 推导为size_t（避免有符号/无符号问题）
多类型容器遍历
std::unordered_map<std::string, float> prices = {{"apple", 1.2f}};
for (auto& [key, value] : prices) { // C++17结构化绑定std::cout << key << ": " << value << "\n";
}
配合decltype使用
int a = 10;
decltype(auto) b = a; // 推导为int（保留引用和const）
自动推导数组长度
int arr[] = {1, 2, 3};
auto len = std::size(arr); // C++17，推导为size_t
简化复杂模板实例
auto matrix = std::vector<std::vector<double>>(3, std::vector<double>(3, 0.0));
类型安全的宏替代
#define MAX(a, b) ({ auto _a = (a); auto _b = (b); _a > _b ? _a : _b; })
配合智能指针
auto uptr = std::make_unique<int>(42); // 推导为std::unique_ptr<int>
避免临时对象
auto result = std::find(vec.begin(), vec.end(), 2); // 推导为std::vector<int>::iterator
类型推导与移动语义
auto str = std::string("Hello");
auto movedStr = std::move(str); // 推导为std::string&&
泛型编程辅助
template<typename T>
auto printTypeInfo(const T& val) {std::cout << typeid(val).name() << "\n";
}
自动推导函数对象
auto greaterThan = [threshold=10](int x) { return x > threshold; };
std::cout << greaterThan(15); // 输出1（true）
配合类型转换
auto intValue = static_cast<int>(3.14); // 显式转换后推导为int
多返回值处理
auto [min, max] = std::minmax({5, 2, 8, 3}); // 推导为std::pair<int, int>
避免类型截断
auto largeNumber = 10000000000LL; // 推导为long long
动态类型检查辅助
std::any data = 42;
if (auto ptr = std::any_cast<int>(&data)) {std::cout << *ptr; // 安全类型检查
}
这些示例覆盖了auto在变量声明、循环、函数返回类型、Lambda表达式等场景的应用，能有效提升代码简洁性和可维护性。注意合理使用以避免降低可读性。
基于C++的移动开发实例
以下是基于C++的移动开发实例，涵盖基础功能、网络通信、传感器交互等场景，适用于Android/iOS平台开发（通常通过NDK或跨平台框架实现）。每个例子均提供核心思路和代码片段：
基础UI交互
例子1：调用系统通知栏
// Android NDK示例
#include <jni.h>
#include <string>extern "C" JNIEXPORT void JNICALL
Java_com_example_app_MainActivity_showNotification(JNIEnv* env, jobject thiz, jstring title) {const char *nativeTitle = env->GetStringUTFChars(title, nullptr);// 通过JNI调用Java的NotificationManagerjclass cls = env->FindClass("android/app/NotificationManager");// 实际代码需补充完整构造逻辑env->ReleaseStringUTFChars(title, nativeTitle);
}
例子2：创建本地对话框
// Qt Quick示例（跨平台）
#include <QMessageBox>void showDialog() {QMessageBox::information(nullptr, "Title", "C++ triggered dialog");
}
硬件访问
例子3：获取电池状态
// Android NDK
extern "C" JNIEXPORT jint JNICALL
Java_com_example_app_BatteryMonitor_getLevel(JNIEnv* env, jobject thiz) {jclass cls = env->GetObjectClass(thiz);jmethodID mid = env->GetMethodID(cls, "getSystemService", "(Ljava/lang/String;)Ljava/lang/Object;");// 实际需通过Java层BatteryManager获取return 75; // 示例值
}
例子4：控制闪光灯
// iOS通过AVFoundation
#import <AVFoundation/AVFoundation>void toggleTorch(bool on) {AVCaptureDevice *device = [AVCaptureDevice defaultDeviceWithMediaType:AVMediaTypeVideo];if ([device hasTorch]) {[device lockForConfiguration:nil];[device setTorchMode: on ? AVCaptureTorchModeOn : AVCaptureTorchModeOff];[device unlockForConfiguration];}
}
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