std::erase_if (std::unordered_multimap)
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< cpp | container | unordered multimap
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std::unordered_multimap (C++23)
(C++17)
(C++17)
(C++20)
erase_if(std::unordered_multimap)
(C++20)
(until C++20)
Deduction guides (C++17)
Defined in header
<unordered_map>
template< class Key, class T, class Hash, class KeyEqual, class Alloc,
(since C++20) class Pred >
std::unordered_multimap <Key, T, Hash, KeyEqual, Alloc>::size_type
erase_if( std::unordered_multimap <Key, T, Hash, KeyEqual, Alloc>& c,
(constexpr since C++26)
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();
[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
Run this code
#include <iostream> #include <unordered_map> void println(auto rem, const auto& 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::unordered_multimap <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) { const auto& [key, value] = item; return (key & 1) == 1; }); println("Erase items with odd keys:\n", data); std::cout << count << " items removed.\n"; }
Possible output:
Original:
{{5, g}, {5, g}, {5, e}, {4, f}, {4, d}, {3, c}, {2, b}, {1, a}}
Erase items with odd keys:
{{4, f}, {4, d}, {2, b}}
5 items removed.