NAME¶

std::map::insert - std::map::insert

Synopsis¶

std::pair<iterator, bool> insert( const value_type& (1)
value );
template< class P > (2) (since C++11)
std::pair<iterator, bool> insert( P&& value );
std::pair<iterator, bool> insert( value_type&& value (3) (since C++17)
);
iterator insert( iterator pos, const value_type& (until C++11)
value );
iterator insert( const_iterator pos, const (since C++11)
value_type& value );
template< class P > (5) (since C++11)
iterator insert( const_iterator pos, P&& value );
iterator insert( const_iterator pos, value_type&& (6) (since C++17)
value ); (4)
template< class InputIt > (7)
void insert( InputIt first, InputIt last );
void insert( std::initializer_list<value_type> ilist (8) (since C++11)
);
insert_return_type insert( node_type&& nh ); (9) (since C++17)
iterator insert( const_iterator pos, node_type&& nh (10) (since C++17)
);

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(hint, std::forward<P>(value)) and only
participates in overload resolution if std::is_constructible<value_type, P&&>::value
== true.
7) 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).
8) 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).
9) 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().
10) 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)

Parameters¶

pos - iterator to the position before which the new element will be inserted
value - element value to insert
first, last - range of elements to insert
ilist - initializer list to insert the values from
nh - a compatible node handle

Type requirements¶

-
InputIt must meet the requirements of LegacyInputIterator.

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)
9) 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().
10) 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.

Exceptions¶

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

This section is incomplete
Reason: cases 7-10

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.
9) Logarithmic in the size of the container, O(log(size())).
10) Amortized constant if the insertion happens in the position just before pos,
logarithmic in the size of the container otherwise.

Notes¶

The hinted insert (4-6) 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.

Example¶

// Run this code

#include <iomanip>
#include <iostream>
#include <map>
#include <string>
using namespace std::literals;

template<typename It>
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

Defect reports

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

DR Applied to Behavior as published Correct behavior
the insertion is required
pos was just a hint, it could be to
LWG 233 C++98 totally ignored be as close as possible to
the
position just prior to pos
the complexity of overload (7) was removed the linear
LWG 264 C++98 required to be linear if requirement
the range [first, last) is sorted in this special case
according to Compare
in the return value of overload (1),
LWG 316 C++98 it was not specified success is
which bool value indicates a indicated by true
successful insertion
LWG 2005 C++11 overloads (2,5) were poorly described improved the description

See also¶

emplace constructs element in-place
(C++11) (public member function)
emplace_hint constructs elements in-place using a hint
(C++11) (public member function)
insert_or_assign inserts an element or assigns to the current element if the key
(C++17) already exists
(public member function)
inserter creates a std::insert_iterator of type inferred from the argument
(function template)

Category:¶

* Todo with reason