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template<class...Args> iterator emplace_hint( const_iterator hint, Args&&...args); | (since C++11) (constexpr since C++26) | |
Inserts a new element into the container as close as possible to the position just beforehint.
The constructors of the key and mapped value are called with exactly the same arguments as supplied to the function, forwarded withstd::forward<Args>(args)....
No iterators or references are invalidated.
Contents |
| hint | - | iterator to the position before which the new element will be inserted |
| args | - | arguments to forward to the constructor of the element |
An iterator to the inserted element, or to the element that prevented the insertion.
If an exception is thrown for any reason, this function has no effect (strong exception safety guarantee).
Logarithmic in the size of the container in general, but amortized constant if the new element is inserted just beforehint.
#include <chrono>#include <cstddef>#include <functional>#include <iomanip>#include <iostream>#include <set> constint n_operations=1005000; std::size_t set_emplace(){std::set<int> set;for(int i=0; i< n_operations;++i) set.emplace(i);return set.size();} std::size_t set_emplace_hint(){std::set<int> set;auto it= set.begin();for(int i=0; i< n_operations;++i){ set.emplace_hint(it, i); it= set.end();}return set.size();} std::size_t set_emplace_hint_wrong(){std::set<int> set;auto it= set.begin();for(int i= n_operations; i>0;--i){ set.emplace_hint(it, i); it= set.end();}return set.size();} std::size_t set_emplace_hint_corrected(){std::set<int> set;auto it= set.begin();for(int i= n_operations; i>0;--i){ set.emplace_hint(it, i); it= set.begin();}return set.size();} std::size_t set_emplace_hint_closest(){std::set<int> set;auto it= set.begin();for(int i=0; i< n_operations;++i) it= set.emplace_hint(it, i);return set.size();} double time_it(std::function<std::size_t()> set_test,constchar* what= nullptr,double ratio=0.0){constauto start=std::chrono::system_clock::now();conststd::size_t setsize= set_test();constauto stop=std::chrono::system_clock::now();conststd::chrono::duration<double,std::milli> time= stop- start;if(what!= nullptr&& setsize>0)std::cout<<std::setw(8)<< time<<" for "<< what<<" (ratio: "<<(ratio==0.0?1.0: ratio/ time.count())<<")\n";return time.count();} int main(){std::cout<<std::fixed<<std::setprecision(2); time_it(set_emplace);// cache warmupconstauto x= time_it(set_emplace,"plain emplace"); time_it(set_emplace_hint,"emplace with correct hint", x); time_it(set_emplace_hint_wrong,"emplace with wrong hint", x); time_it(set_emplace_hint_corrected,"corrected emplace", x); time_it(set_emplace_hint_closest,"emplace using returned iterator", x);}
Possible output:
392.25ms for plain emplace (ratio: 1.00) 97.15ms for emplace with correct hint (ratio: 4.04)387.52ms for emplace with wrong hint (ratio: 1.01) 84.80ms for corrected emplace (ratio: 4.63) 83.67ms for emplace using returned iterator (ratio: 4.69)
(C++11) | constructs element in-place (public member function)[edit] |
| inserts elementsor nodes(since C++17) (public member function)[edit] |
