template <class... Args> pair<iterator, bool> try_emplace(const key_type& k, Args&&... args); | (1) | (since C++17) |
template <class... Args> pair<iterator, bool> try_emplace(key_type&& k, Args&&... args); | (2) | (since C++17) |
template <class... Args> iterator try_emplace(const_iterator hint, const key_type& k, Args&&... args); | (3) | (since C++17) |
template <class... Args> iterator try_emplace(const_iterator hint, key_type&& k, Args&&... args); | (4) | (since C++17) |
1) If a key equivalent to
k already exists in the container, does nothing. Otherwise, behaves like emplace except that the element is constructed as value_type(std::piecewise_construct, std::forward_as_tuple(k), std::forward_as_tuple(forward<Args>(args)...)) 2) If a key equivalent to
k already exists in the container, does nothing. Otherwise, behaves like emplace except that the element is constructed as value_type(std::piecewise_construct, std::forward_as_tuple(std::move(k)), std::forward_as_tuple(forward<Args>(args)...)) 3) If a key equivalent to
k already exists in the container, does nothing. Otherwise, behaves like emplace_hint except that the element is constructed as value_type(std::piecewise_construct, std::forward_as_tuple(k), std::forward_as_tuple(forward<Args>(args)...)) 4) If a key equivalent to
k already exists in the container, does nothing. Otherwise, behaves like emplace_hint except that the element is constructed as value_type(std::piecewise_construct, std::forward_as_tuple(std::move(k)), std::forward_as_tuple(forward<Args>(args)...)) No iterators or references are invalidated.
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 |
Return value
1,2) Same as for emplace
3,4) Same as for emplace_hint
Complexity
1,2) Same as for emplace
3,4) Same as for emplace_hint
Notes
Unlike insert or emplace, these functions do not steal from move-only 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).
Example
See also
| (C++11) | constructs element in-place (public member function) |
| (C++11) | constructs elements in-place using a hint (public member function) |
| inserts elements (public member function) |
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