Unable to step into

#include <unordered_map>
#include <iostream>
#include <QString>

int main(int argc, char *argv[])
{
    std::unordered_map<int, QString> mapq;
    mapq[1] = "one";
    mapq[2] = "two";
    mapq[3] ="thre";

    size_t i = 0;
    // size_t i = 0;
    for (const auto &md : mapq) {
        std::cout << "{ key: " << md.first << ", value: " << md.second.toStdString();
        if (++i < mapq.size())
            std::cout << " }, " << std::endl;
        else
            std::cout << " }" << std::endl;
    }

    return 0;
}