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Showing content from https://en.cppreference.com/w/cpp/language/../algorithm/../../cpp/container/map/try_emplace.html below:

std::map<Key,T,Compare,Allocator>::try_emplace - cppreference.com

template< class... Args >
std::pair<iterator, bool> try_emplace( const Key& k, Args&&... args ); (1) (since C++17) template< class... Args >
std::pair<iterator, bool> try_emplace( Key&& k, Args&&... args ); (2) (since C++17) template< class K, class... Args >
std::pair<iterator, bool> try_emplace( K&& k, Args&&... args ); (3) (since C++26)

template< class... Args >
iterator try_emplace( const_iterator hint, const Key& k, Args&&... args );

(4) (since C++17)

template< class... Args >
iterator try_emplace( const_iterator hint, Key&& k, Args&&... args );

(5) (since C++17)

template< class K, class... Args >
iterator try_emplace( const_iterator hint, K&& k, Args&&... args );

(6) (since C++26)

If a key equivalent to k already exists in the container, does nothing. Otherwise, inserts a new element into the container with key k and value constructed with args. In such case:

1-6)

If

value_type

is not

EmplaceConstructible

into

map

from the corresponding expression, the behavior is undefined.

3)

This overload participates in overload resolution only if all following conditions are satisfied:

If equal_range(u.first) == equal_range(k) is false, the behavior is undefined, where u is the new element to be inserted.

6) This overload participates in overload resolution only if the qualified-id Compare::is_transparent is valid and denotes a type.

If equal_range(u.first) == equal_range(k) is false, the behavior is undefined, where u is the new element to be inserted.

No iterators or references are invalidated.

[edit] Parameters k - the key used both to look up and to insert if not found hint - iterator to the position before which the new element will be inserted args - arguments to forward to the constructor of the element [edit] Return value 1-3)

Same as for

emplace

:

A pair consisting of an iterator to the inserted element (or to the element that prevented the insertion) and a

bool

value set to

true

if and only if the insertion took place.

4-6)

Same as for

emplace_hint

:

An iterator to the inserted element, or to the element that prevented the insertion.

[edit] Complexity 1-3)

Same as for

emplace

:

Logarithmic in the size of the container.

4-6)

Same as for

emplace_hint

:

Logarithmic in the size of the container in general, but amortized constant if the new element is inserted just before

hint

.

[edit] Notes

Unlike insert or emplace, these functions do not move from rvalue arguments if the insertion does not happen, which makes it easy to manipulate maps whose values are move-only types, such as std::map<std::string, std::unique_ptr<foo>>. In addition, try_emplace treats the key and the arguments to the mapped_type separately, unlike emplace, which requires the arguments to construct a value_type (that is, a std::pair).

Overloads (3) and (6) can be called without constructing an object of type Key.

[edit] Example 
#include <iostream>
#include <string>
#include <map>
#include <utility>
 
void print_node(const auto& node)
{
    std::cout << '[' << node.first << "] = " << node.second << '\n';
}
 
void print_result(auto const& pair)
{
    std::cout << (pair.second ? "inserted: " : "ignored:  ");
    print_node(*pair.first);
}
 
int main()
{
    using namespace std::literals;
    std::map<std::string, std::string> m;
 
    print_result(m.try_emplace("a", "a"s));
    print_result(m.try_emplace("b", "abcd"));
    print_result(m.try_emplace("c", 10, 'c'));
    print_result(m.try_emplace("c", "Won't be inserted"));
 
    for (const auto& p : m)
        print_node(p);
}

Output:

inserted: [a] = a
inserted: [b] = abcd
inserted: [c] = cccccccccc
ignored:  [c] = cccccccccc
[a] = a
[b] = abcd
[c] = cccccccccc
[edit] See also constructs element in-place
(public member function) [edit] constructs elements in-place using a hint
(public member function) [edit] inserts elements or nodes(since C++17)
(public member function) [edit]

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