lst-0100-book.cpp
// https://godbolt.org/z/bxW63jPor
#include <map> // the main thing
#include <iostream> // for output
#include <string> // often used for key or target
using std::multimap; using std::cout; using std::string;
template<typename Key, typename Trg, typename Cmp>
std::ostream& operator<<=(std::ostream&os, const multimap<Key,Trg,Cmp>&data){
for(auto &e : data) {
os << e.first << ":" << e.second << ' ';
}
return os << '\n'; // '<<=' instead of '<<' for line break
}
int main() {
// Example code here
}