Question

If a timestamp is NOT in a map stored with timestamps I would like to find the closest matching timestamp in the map and use the closest value as a key. I have the basic structure setup for what I’m trying to do i’m just not sure how to find the nearest timestamp

typedef std::map<std::string,int>  Map;
Map::iterator it;
Map my_map;

my_map["2010-01-26 17:02:12"]= 1;
my_map["2010-01-25 08:55:29"]= 2;
my_map["2010-01-24 08:55:29"]= 3;

string timestamp = "2010-01-24 08:55:30"; // would return 3
string timestamp1 = "2010-01-27 01:55:30"; // would return 1

  it = my_map.find(timestamp); 
     if(it == my_map.end()){
       //not sure how to approach this
   }    

update

I’m trying to avoid converting a fairly large code base from std::string to uint64_t although it would increase performance, it’s not that big of an issue,

I can’t get the std::map::lower_bound or std::map::upper_bound solutions to work
here is my attempt on IDE ONE,

http://ideone.com/MnRLIH

Answer 1

You can probably get what you need with std::map::lower_bound or std::map::upper_bound, either of which is O(log N) complexity.

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Also, strongly consider storing your timestamps as, say, a uint64_t rather than a string. This would greatly reduce the amount of computation to compare and process.