The multimap in C++ seems to work really odd, i would like to know why
#include <iostream>
#include <unordered_map>
using namespace std;
typedef unordered_multimap<char,int> MyMap;
int main(int argc, char **argv)
{
MyMap map;
map.insert(MyMap::value_type('a', 1));
map.insert(MyMap::value_type('b', 2));
map.insert(MyMap::value_type('c', 3));
map.insert(MyMap::value_type('d', 4));
map.insert(MyMap::value_type('a', 7));
map.insert(MyMap::value_type('b', 18));
for(auto it = map.begin(); it != map.end(); it++) {
cout << it->first << '\t';
cout << it->second << endl;
}
cout << "all values to a" << endl;
for(auto it = map.find('a'); it != map.end(); it++) {
cout << it->first << '\t' << it->second << endl;
}
}
this is the output:
c 3
d 4
a 1
a 7
b 2
b 18
all values to a
a 1
a 7
b 2
b 18
why does the output still contain anything with b as the key when I am explicitly asking for 'a'? Is this a compiler or stl bug?
find
, as implemented, returns an iterator for the first element which matches the key in the multimap (as with any other map). You're likely looking for equal_range
:
// Finds a range containing all elements whose key is k.
// pair<iterator, iterator> equal_range(const key_type& k)
auto its = map.equal_range('a');
for (auto it = its.first; it != its.second; ++it) {
cout << it->first << '\t' << it->second << endl;
}