Hi :icon_smile:

I have written a C++ program which works very fine. The problem comes in terms of efficiency and speed. I am using a multimap which is required for my type of requirement.


Now the problem is that for files more than 100 MB it takes a lot of time to load the data into multimap which slows down the program.

I am inserting Strings into the multimap. I even used references of string for insertion into multimap but not of much help.

My question is more conceptual. So what do I need to do to speed up my program ?

If I insert my strings into a vector and then insert that vector into multimap - will that increase the speed of my program ?

I mean something like this:


Would appreciate any advice

Thanks in advance :-/

All the thing mentioned by you could speed up your program. But the main question is: Why are you loading 100 mb of data in your memory? This might be a good time to review your algorithm!

Lets suppose this code. My requirement is like the code below. Is there a way I can do such a thing using vector ? without loading into memory ?

// multimap::count
#include <iostream>
#include <map>
using namespace std;

int main ()
  multimap<string,string> mymm;
  multimap<string,string>::iterator it;
  vector<string> vec1;
  vector<string>::iterator itv;

  mymm.insert(pair<string,string>("andrew","andrew S* years old"));
  mymm.insert(pair<string,string>("peter","peter 1 years old"));
  mymm.insert(pair<string,string>("peter","peter 2 years old"));
  mymm.insert(pair<string,string>("peter","peter 3 years old"));
  mymm.insert(pair<string,string>("mathew","mathew 1 years old"));
  mymm.insert(pair<string,string>("mathew","mathew 2 years old"));
  mymm.insert(pair<string,string>("Dsouza","Dsouza S* years old"));
  mymm.insert(pair<string,string>("Austin","Austin 1 years old"));
  mymm.insert(pair<string,string>("Austin","Austin 2 years old"));
  mymm.insert(pair<string,string>("Austin","Austin 3 years old"));
  mymm.insert(pair<string,string>("Austin","Austin 4 years old"));
  mymm.insert(pair<string,string>("Austin","Austin 5 years old"));
  mymm.insert(pair<string,string>("David","David S* years old"));
  mymm.insert(pair<string,string>("John","John 1 years old"));
  mymm.insert(pair<string,string>("John","John 2 years old"));

    for(itv=vec1.begin(); itv < vec1.end(); itv++)
       int i = 0;
       int k = 0;
    for (it=mymm.equal_range(*itv).first; it!=mymm.equal_range(*itv).second; ++it)
            cout << "one"<<"\t"<<(*it).second << endl;
         else if(i>0 && i < ( mymm.count(*itv) - 1)){
            cout << "middle"<<"\t"<<(*it).second << endl;
         else if(i !=0 ){     
            cout << "end"<<"\t"<<(*it).second << endl;
      else if((int)mymm.count(*itv)==1){      
            cout << "Single"<<"\t"<<(*it).second << endl;   
      else if((int)mymm.count(*itv)==2){      
            cout << "one" << "\t"<< (*it).second << endl;
         else {
            cout << "end" << "\t" << (*it).second << endl; 
  return 0;


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