linux获取cpu使用率（sy%+us%）

float getCpuUsage() 
{
    // C++11兼容的元组解包
    typedef std::tuple<unsigned long long, unsigned long long, unsigned long long> CpuTuple;

    auto parseCpuLine = [](const std::string& line) -> CpuTuple {
        std::istringstream iss(line);
        iss.ignore(3, ' '); // 跳过 "cpu"
        while (iss.peek() == ' ' || iss.peek() == '\t') iss.ignore();

        // 解析所有字段（含 steal、guest、guest_nice）
        unsigned long long user = 0, nice = 0, system = 0, idle = 0,
            iowait = 0, irq = 0, softirq = 0, steal = 0,
            guest = 0, guest_nice = 0;
        iss >> user >> nice >> system >> idle >> iowait >> irq >> softirq
            >> steal >> guest >> guest_nice;

        // 计算用户态和系统态时间（us% = user + nice, sy% = system + irq + softirq）
        unsigned long long us_time = user + nice;
        unsigned long long sy_time = system + irq + softirq;
        // 总时间包含所有字段 [11](@ref)
        unsigned long long total = user + nice + system + idle + iowait +
            irq + softirq + steal + guest + guest_nice;

        return std::make_tuple(us_time, sy_time, total);
    };

    // 第一次采样
    std::ifstream file1("/proc/stat");
    std::string line1;
    std::getline(file1, line1);
    unsigned long long us1, sy1, total1;
    std::tie(us1, sy1, total1) = parseCpuLine(line1);

    sleep(1);

    // 第二次采样
    std::ifstream file2("/proc/stat");
    std::string line2;
    std::getline(file2, line2);
    unsigned long long us2, sy2, total2;
    std::tie(us2, sy2, total2) = parseCpuLine(line2);

    // 计算差值
    const unsigned long long total_diff = total2 - total1;
    if (total_diff == 0) return 0.0f;

    const unsigned long long us_diff = us2 - us1;
    const unsigned long long sy_diff = sy2 - sy1;

    return static_cast<float>(us_diff + sy_diff) * 100.0f / total_diff;
}