CODEWITHSUNDEEP
c++
rplantiko
rplantiko

Reputation: 2738

Continue looping after a given iterator position in an std::map

I want to loop over all items of a map that follow a given item.

Unfortunately, I get the error: no match for 'operator+' (operand types are 'std::_Rb_tree_iterator >' and 'int').

What am I doing wrong?

#include <iostream>
#include <map>

int main ()
{
  std::map<char,int> m = {
    {'a',1},{'b',2},{'c',3},{'d',4},
  };

  // Position at 'b' (the 'given item')
  auto it = m.find('b');

  // Output everything after 'b':
  for (auto it1=it+1; it1!=m.end(); ++it1) {
    std::cout << it1->first << " => " << it1->second << '\n';
  }

  return 0;
}

Upvotes: 1

Views: 42

Answers (2)

aspen100
aspen100

Reputation: 965

++ works just as well: 

 // Output everything after 'b':
    for (auto it1=++it; it1!=m.end(); ++it1) {
      std::cout << it1->first << " => " << it1->second << '\n';
    }

Upvotes: 1

Vaughn Cato
Vaughn Cato

Reputation: 64308

The iterator for a std::map is not random-access, so it doesn't have an operator+(). You need to use std::next() instead:

 for (auto it1=std::next(it); it1!=m.end(); ++it1) {
    std::cout << it1->first << " => " << it1->second << '\n';
 }

Upvotes: 3

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