can someone please explain lower_bound function in map stl in c++?i am confused in this example given on c++ site

Question

// map::lower_bound/upper_bound
#include <iostream>
#include <map>

int main ()
{
std::map<char,int> mymap;
std::map<char,int>::iterator itlow,itup;

mymap['a']=20;
mymap['b']=40;
mymap['c']=60;
mymap['d']=80;
mymap['e']=100;

itlow=mymap.lower_bound ('b'); // itlow points to b
itup=mymap.upper_bound ('d'); // itup points to e (not d!)

mymap.erase(itlow,itup); // erases [itlow,itup)

// print content:
for (std::map<char,int>::iterator it=mymap.begin(); it!=mymap.end(); ++it)
std::cout << it->first << " => " << it->second << '\n';

return 0;
}

Answer 1

Bahubali as you might be aware that map has key and value... if you do lowebound on map, it searches for key and returns iterator based on value as per below logic :

for example, map has key as 1,3,4 and 5..

now, lower_bound (2) will give you iterator of key as 3 because 1 is not equal to or more than searched value (2 in our case)

lower_bound (3) will give you iterator of key as 3 because 1 is not equal to or more than searched value (3 in our case), but 3 is equal to 3