C++写个函数，实时获取windows的cpu使用率

在C++中，获取Windows系统的CPU使用率通常需要借助第三方库，如Boost或其他系统性能监控API。这里我将提供一个使用`boost::process`库的例子，它可以帮助我们读取性能计数器数据。请注意，你需要先安装并链接这个库。

#include <boost/process.hpp>
#include <windows.h>

double get_cpu_usage() {
    boost::process::winapi::performance_counters pc;
    std::vector<boost::process::winapi::counter> counters = {
        {"% Processor Time", "", "Processor"}
    };

    if (!pc.initialize()) {
        throw std::runtime_error("Failed to initialize performance counters");
    }

    pc.select(counters);
    double cpu_total = 0.0;

    for (auto &counter : pc.counters()) {
        DWORD value;
        if (!counter.read(&value)) {
            throw std::runtime_error("Failed to read counter value");
        }
        // Windows CPU usage is the total processor time divided by the number of logical processors
        // Note that this can be an approximation due to the way Windows reports data
        cpu_total += static_cast<double>(value) / GetLogicalProcessorCount();
    }

    return cpu_total / static_cast<double>(counters.size());
}

int main() {
    try {
        double usage = get_cpu_usage();
        std::cout << "Current CPU usage: " << usage * 100 << "%" << std::endl;
    } catch (const std::exception &e) {
        std::cerr << "Error: " << e.what() << std::endl;
    }

    return 0;
}