标准差的输出为NaN - C++

#include <iostream>
#include <vector>
#include <cmath>
#include <numeric> // for std::accumulate

double calculateStandardDeviation(const std::vector<double>& data) {
    if (data.empty()) {
        return std::numeric_limits<double>::quiet_NaN();
    }

    double sum = std::accumulate(data.begin(), data.end(), 0.0);
    double mean = sum / data.size();

    double variance = 0.0;
    for (double value : data) {
        variance += (value - mean) * (value - mean);
    }
    variance /= data.size();

    if (variance < 0) {
        return std::numeric_limits<double>::quiet_NaN();
    }

    return std::sqrt(variance);
}

int main() {
    std::vector<double> data = {1.0, 2.0, 3.0, 4.0, 5.0};

    double stdDev = calculateStandardDeviation(data);
    if (std::isnan(stdDev)) {
        std::cout << "标准差计算结果为NaN" << std::endl;
    } else {
        std::cout << "标准差: " << stdDev << std::endl;
    }

    return 0;
}