human_readable_duration.cpp

#include <string>
#include <sstream>
#include <vector>
#include <iomanip>

std::string human_readable_duration(int num_seconds) {
    static int divisions[3] = {60, 60, 24};
    std::stringstream buf;
    if (num_seconds < divisions[0]) {
        buf << num_seconds << " seconds";
    } else {
        std::vector<int> components;
        for (int d = 0; d < sizeof(divisions)/sizeof(divisions[0]) && num_seconds > 0; num_seconds /= divisions[d++]) {
            int comp = num_seconds % divisions[d];
            components.push_back(comp);
        }
        if (num_seconds > 0) components.push_back(num_seconds);
        std::vector<int>::const_reverse_iterator iter = components.rbegin();
        buf << *(iter++);
        for (; iter != components.rend(); ++iter) {
            buf << ":" << std::setw(2) << std::setfill('0') << *iter;
        }
    }
    return buf.str();
}