std::erase, std::erase_if(std::list)
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Defined in header
<list>
(1)
template< class T, class Alloc, class U >
(since C++20) typename std::list <T, Alloc>::size_type
(until C++26)
template< class T, class Alloc, class U = T >
(since C++26)
constexpr typename std::list <T, Alloc>::size_type
template< class T, class Alloc, class Pred >
(2)
(since C++20) typename std::list <T, Alloc>::size_type
(constexpr since C++26)
1) Erases all elements that compare equal to value from the container c. Equivalent to
return c.remove_if([&](const auto& elem) -> bool { return elem == value; });.
2) Erases all elements that satisfy the predicate pred from the container c. Equivalent to
return c.remove_if(pred);.
[edit] Parameters
c
-
container from which to erase
value
-
value to be removed
pred
-
unary predicate which returns true if the element should be erased.
The expression pred(v) must be convertible to bool for every argument v of type (possibly const) T, regardless of value category, and must not modify v. Thus, a parameter type of T&is not allowed, nor is T unless for T a move is equivalent to a copy(since C++11).
[edit] Return value
The number of erased elements.
[edit] Complexity
Linear.
Notes
Unlike std::list::remove , erase accepts heterogeneous types and does not force a conversion to the container's value type before invoking the == operator.
| Feature-test macro | Value | Std | Feature |
|---|---|---|---|
__cpp_lib_algorithm_default_value_type |
202403 |
(C++26) | List-initialization for std::erase
|
[edit] Example
Run this code
#include <complex> #include <iostream> #include <numeric> #include <string_view> #include <list> void println(std::string_view comment, const auto& c) { std::cout << comment << '['; bool first{true}; for (const auto& x : c) std::cout << (first ? first = false, "" : ", ") << x; std::cout << "]\n"; } int main() { std::list <char> cnt(10); std::iota (cnt.begin(), cnt.end(), '0'); println("Initially, cnt = ", cnt); std::erase (cnt, '3'); println("After erase '3', cnt = ", cnt); auto erased = std::erase_if (cnt, [](char x) { return (x - '0') % 2 == 0; }); println("After erase all even numbers, cnt = ", cnt); std::cout << "Erased even numbers: " << erased << '\n'; std::list <std::complex <double>> nums{{2, 2}, {4, 2}, {4, 8}, {4, 2}}; #ifdef __cpp_lib_algorithm_default_value_type std::erase (nums, {4, 2}); #else std::erase (nums, std::complex <double>{4, 2}); #endif println("After erase {4, 2}, nums = ", nums); }
Output:
Initially, cnt = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
After erase '3', cnt = [0, 1, 2, 4, 5, 6, 7, 8, 9]
After erase all even numbers, cnt = [1, 5, 7, 9]
Erased even numbers: 5
After erase {4, 2}, nums = [(2,2), (4,8)]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 4135 | C++20 | the return type of the lambda predicate used was deduced from predicate arguments |
the return type is explicitly specified as bool |