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std::erase_if (std::map)

From cppreference.com
< cpp‎ | container‎ | map
 
 
 
 
Defined in header <map>
template< class Key, class T, class Compare, class Alloc,

          class Pred >
std::map<Key, T, Compare, Alloc>::size_type
    erase_if( std::map<Key, T, Compare, Alloc>& c,

              Pred pred );
(since C++20)

Erases all elements that satisfy the predicate pred from c.

Equivalent to

auto old_size = c.size();
for (auto first = c.begin(), last = c.end(); first != last;)
{
    if (pred(*first))
        first = c.erase(first);
    else
        ++first;
}
return old_size - c.size();

Contents

[edit] Parameters

c - container from which to erase
pred - predicate that returns true if the element should be erased

[edit] Return value

The number of erased elements.

[edit] Complexity

Linear.

[edit] Example

#include <iostream>
#include <map>
 
void println(auto rem, auto const& container)
{
    std::cout << rem << '{';
    for (char sep[]{0, ' ', 0}; const auto& [key, value] : container)
        std::cout << sep << '{' << key << ", " << value << '}', *sep = ',';
    std::cout << "}\n";
}
 
int main()
{
    std::map<int, char> data
    {
        {1, 'a'}, {2, 'b'}, {3, 'c'}, {4, 'd'},
        {5, 'e'}, {4, 'f'}, {5, 'g'}, {5, 'g'},
    };
    println("Original:\n", data);
 
    const auto count = std::erase_if(data, [](const auto& item)
    {
        auto const& [key, value] = item;
        return (key & 1) == 1;
    });
 
    println("Erase items with odd keys:\n", data);
    std::cout << count << " items removed.\n";
}

Output:

Original:
{{1, a}, {2, b}, {3, c}, {4, d}, {5, e}}
Erase items with odd keys:
{{2, b}, {4, d}}
3 items removed.

[edit] See also

removes elements satisfying specific criteria
(function template) [edit]