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is there an iterator across unique keys in a std::multimap?

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无人及你
无人及你 2020-11-29 08:18

Is there a simple or standard way to have a multimap iterator which iterate across unique keys in a multimap?

i.e. for a set that looks like: {1, \"a\"}, {1, \

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  • 天涯浪人
    天涯浪人 (楼主)
    2020-11-29 08:30

    You can use upper_bound to increment the iterator position instead of ++:

    #include 
#include 
#include 

using namespace std;

int main()
{
  multimap mm;
  mm.insert(make_pair(1, "a"));
  mm.insert(make_pair(1, "lemon"));
  mm.insert(make_pair(2, "peacock"));
  mm.insert(make_pair(3, "angel"));

  for( auto it = mm.begin(), end = mm.end();
       it != end;
       it = mm.upper_bound(it->first)
  )
    cout << it->first << ' ' << it->second << endl;
  return 0;
}

    This results in:

    1 a
2 peacock
3 angel

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