map::emplace_hint
Inserts an element constructed in place (no copy or move operations are performed), with a placement hint.
template<class... Args>
iterator emplace_hint(
const_iterator where,
Args&&... args);
Parameters
Parameter |
Description |
args |
The arguments forwarded to construct an element to be inserted into the map unless the map already contains that element or, more generally, unless it already contains an element whose key is equivalently ordered. |
where |
The place to start searching for the correct point of insertion. (If that point immediately precedes where, insertion can occur in amortized constant time instead of logarithmic time.) |
Return Value
An iterator to the newly inserted element.
If the insertion failed because the element already exists, returns an iterator to the existing element with its key.
Remarks
No iterators or references are invalidated by this function.
During emplacement, if an exception is thrown, the container's state is not modified.
The value_type of an element is a pair, so that the value of an element will be an ordered pair with the first component equal to the key value and the second component equal to the data value of the element.
Example
// map_emplace.cpp
// compile with: /EHsc
#include <map>
#include <string>
#include <iostream>
using namespace std;
template <typename M> void print(const M& m) {
cout << m.size() << " elements: " << endl;
for (const auto& p : m) {
cout << "(" << p.first << "," << p.second << ") ";
}
cout << endl;
}
int main()
{
map<string, string> m1;
// Emplace some test data
m1.emplace("Anna", "Accounting");
m1.emplace("Bob", "Accounting");
m1.emplace("Carmine", "Engineering");
cout << "map starting data: ";
print(m1);
cout << endl;
// Emplace with hint
// m1.end() should be the "next" element after this emplacement
m1.emplace_hint(m1.end(), "Doug", "Engineering");
cout << "map modified, now contains ";
print(m1);
cout << endl;
}
Output
map starting data: 3 elements:
(Anna,Accounting) (Bob,Accounting) (Carmine,Engineering)
map modified, now contains 4 elements:
(Anna,Accounting) (Bob,Accounting) (Carmine,Engineering) (Doug,Engineering)
Requirements
Header: <map>
Namespace: std