std::map<Key,T,Compare,Allocator>::insert - cppreference.com (original) (raw)

Inserts element(s) into the container, if the container doesn't already contain an element with an equivalent key.

1-3) Inserts value.

Overload (2) is equivalent to emplace(std::forward<P>(value)) and only participates in overload resolution if std::is_constructible<value_type, P&&>::value == true.

4-6) Inserts value in the position as close as possible to the position just prior to pos.

Overload (5) is equivalent to emplace_hint(pos, std::forward<P>(value)) and only participates in overload resolution if std::is_constructible<value_type, P&&>::value == true.

1. Inserts elements from range [first, last). If multiple elements in the range have keys that compare equivalent, it is unspecified which element is inserted (pending LWG2844).

2. Inserts elements from initializer list ilist. If multiple elements in the range have keys that compare equivalent, it is unspecified which element is inserted (pending LWG2844).

3. If nh is an empty node handle, does nothing. Otherwise, inserts the element owned by nh into the container , if the container doesn't already contain an element with a key equivalent to nh.key(). The behavior is undefined if nh is not empty and get_allocator() != nh.get_allocator().

4. If nh is an empty node handle, does nothing and returns the end iterator. Otherwise, inserts the element owned by nh into the container, if the container doesn't already contain an element with a key equivalent to nh.key(), and returns the iterator pointing to the element with key equivalent to nh.key()(regardless of whether the insert succeeded or failed). If the insertion succeeds, nh is moved from, otherwise it retains ownership of the element. The element is inserted as close as possible to the position just prior to pos. The behavior is undefined if nh is not empty and get_allocator() != nh.get_allocator().

No iterators or references are invalidated. If the insertion is successful, pointers and references to the element obtained while it is held in the node handle are invalidated, and pointers and references obtained to that element before it was extracted become valid.(since C++17)

Contents

• 1 Parameters
• 2 Return value
• 3 Exceptions
• 4 Complexity
• 5 Notes
• 6 Example
• 7 Defect reports
• 8 See also

[edit] Parameters

[edit] Return value

1-3) 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) An iterator to the inserted element, or to the element that prevented the insertion.

7,8) (none)

1. An object of insert_return_type with the members initialized as follows:

• If nh is empty, inserted is false, position is end(), and node is empty.
• Otherwise if the insertion took place, inserted is true, position points to the inserted element, and node is empty.
• If the insertion failed, inserted is false, node has the previous value of nh, and position points to an element with a key equivalent to nh.key().

1. End iterator if nh was empty, iterator pointing to the inserted element if insertion took place, and iterator pointing to an element with a key equivalent to nh.key() if it failed.

[edit] Exceptions

1-6) If an exception is thrown by any operation, the insertion has no effect.

[edit] Complexity

1-3) Logarithmic in the size of the container, O(log(size())).

4-6) Amortized constant if the insertion happens in the position just after(until C++11)before(since C++11) pos, logarithmic in the size of the container otherwise.

7,8) O(N·log(size() + N)), where N is the number of elements to insert.

1. Logarithmic in the size of the container, O(log(size())).

2. Amortized constant if the insertion happens in the position just before pos, logarithmic in the size of the container otherwise.

[edit] Notes

The hinted insert ((4-6) and (10)) does not return a boolean in order to be signature-compatible with positional insert on sequential containers, such as std::vector::insert. This makes it possible to create generic inserters such as std::inserter. One way to check success of a hinted insert is to compare size() before and after.

[edit] Example

#include #include #include #include using namespace std::literals;   template void print_insertion_status(It it, bool success) { std::cout << "Insertion of " << it->first << (success ? " succeeded\n" : " failed\n"); }   int main() { std::map<std::string, float> heights;   // Overload 3: insert from rvalue reference const auto [it_hinata, success] = heights.insert({"Hinata"s, 162.8}); print_insertion_status(it_hinata, success);   { // Overload 1: insert from lvalue reference const auto [it, success2] = heights.insert(*it_hinata); print_insertion_status(it, success2); } { // Overload 2: insert via forwarding to emplace const auto [it, success] = heights.insert(std::pair{"Kageyama", 180.6}); print_insertion_status(it, success); } { // Overload 6: insert from rvalue reference with positional hint const std::size_t n = std::size(heights); const auto it = heights.insert(it_hinata, {"Azumane"s, 184.7}); print_insertion_status(it, std::size(heights) != n); } { // Overload 4: insert from lvalue reference with positional hint const std::size_t n = std::size(heights); const auto it = heights.insert(it_hinata, *it_hinata); print_insertion_status(it, std::size(heights) != n); } { // Overload 5: insert via forwarding to emplace with positional hint const std::size_t n = std::size(heights); const auto it = heights.insert(it_hinata, std::pair{"Tsukishima", 188.3}); print_insertion_status(it, std::size(heights) != n); }   auto node_hinata = heights.extract(it_hinata); std::map<std::string, float> heights2;   // Overload 7: insert from iterator range heights2.insert(std::begin(heights), std::end(heights));   // Overload 8: insert from initializer_list heights2.insert({{"Kozume"s, 169.2}, {"Kuroo", 187.7}});   // Overload 9: insert node const auto status = heights2.insert(std::move(node_hinata)); print_insertion_status(status.position, status.inserted);   node_hinata = heights2.extract(status.position); { // Overload 10: insert node with positional hint const std::size_t n = std::size(heights2); const auto it = heights2.insert(std::begin(heights2), std::move(node_hinata)); print_insertion_status(it, std::size(heights2) != n); }   // Print resulting map std::cout << std::left << '\n'; for (const auto& [name, height] : heights2) std::cout << std::setw(10) << name << " | " << height << "cm\n"; }

Output:

Insertion of Hinata succeeded Insertion of Hinata failed Insertion of Kageyama succeeded Insertion of Azumane succeeded Insertion of Hinata failed Insertion of Tsukishima succeeded Insertion of Hinata succeeded Insertion of Hinata succeeded   Azumane | 184.7cm Hinata | 162.8cm Kageyama | 180.6cm Kozume | 169.2cm Kuroo | 187.7cm Tsukishima | 188.3cm

[edit] Defect reports

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

[edit] See also