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std::map<Key,T,Compare,Allocator>::erase

From cppreference.com
< cpp‎ | container‎ | map
 
 
 
 
(1)
iterator erase( iterator pos );
iterator erase( const_iterator pos );
(since C++11)
(2)
iterator erase( iterator first, iterator last );
(until C++11)
iterator erase( const_iterator first, const_iterator last );
(since C++11)
size_type erase( const Key& key );
(3)
template< class K >
size_type erase( K&& x );
(4) (since C++23)

Removes specified elements from the container.

1) Removes the element at pos.
2) Removes the elements in the range [first; last), which must be a valid range in *this.
3) Removes the element (if one exists) with the key equivalent to key.
4) Removes the element (if one exists) with key that compares equivalent to the value x. This overload participates in overload resolution only if the qualified-id Compare::is_transparent is valid and denotes a type, and neither iterator nor const_iterator is implicitly convertible from K. It allows calling this function without constructing an instance of Key.

References and iterators to the erased elements are invalidated. Other references and iterators are not affected.

The iterator pos must be valid and dereferenceable. Thus the end() iterator (which is valid, but is not dereferenceable) cannot be used as a value for pos.

Contents

[edit] Parameters

pos - iterator to the element to remove
first, last - range of elements to remove
key - key value of the elements to remove
x - a value of any type that can be transparently compared with a key denoting the elements to remove

[edit] Return value

1-2) (none) (until C++11)Iterator following the last removed element. (since C++11)
3,4) Number of elements removed (0 or 1).

[edit] Exceptions

1,2) Throws nothing.
3,4) Any exceptions thrown by the Compare object.

[edit] Complexity

Given an instance c of map:

1) Amortized constant
2) log(c.size()) + std::distance(first, last)
3) log(c.size()) + c.count(key)
4) log(c.size()) + c.count(x)

[edit] Notes

Feature-test macro Value Std Comment
__cpp_lib_associative_heterogeneous_erasure 202110L (C++23) Heterogeneous erasure; overload (4)

[edit] Example

#include <map>
#include <iostream>
 
int main()
{
    std::map<int, std::string> c =
    {
        {1, "one" }, {2, "two" }, {3, "three"},
        {4, "four"}, {5, "five"}, {6, "six"  }
    };
 
    // erase all odd numbers from c
    for (auto it = c.begin(); it != c.end();)
    {
        if (it->first % 2 != 0)
            it = c.erase(it);
        else
            ++it;
    }
 
    for (auto& p : c)
        std::cout << p.second << ' ';
}

Output:

two four six

[edit] Defect reports

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

DR Applied to Behavior as published Correct behavior
LWG 130 C++98 the return type of overloads (1) and (2) was void (it
conflicts with the general erase() requirement on containers)
corrected to iterator
LWG 2059 C++11 overload for one const_iterator introduced new ambiguity overload for iterator added

[edit] See also

clears the contents
(public member function) [edit]