Sort a huge set of log files in C++ and STL

you are given a huge set of log files sorted by timestamp and you need to merge them. You have unlimited disk, but fixed amount of memory. In case of ties, break it by consider a progressive number for the log files

Solution: 

good to recall how a min-heap is defined in STL, it's just an heap with a custom comparison. An heap is nothing more that a normal std::vector and you build it with std::make_heap, std::push_back, std::push_heap(), std::front(), std::pop_heap(). It's always a bit confusing for me to consider that you need to push_back in the vector and than push_heap, but that's not so strange considering that an heap is built upon the vector itself ;-)

   bool greater (const std::pair & a, const std::pair & b)