std::erase, std::erase_if(std::list)
From cppreference.com
| Defined in header <list>
|
||
template< class T, class Alloc, class U >
std::list<T, Alloc>::size_type
erase( std::list<T, Alloc>& c, const U& value );
|
(1) | (since C++20) (until C++26) |
template< class T, class Alloc, class U = T >
std::list<T, Alloc>::size_type
erase( std::list<T, Alloc>& c, const U& value );
|
(since C++26) | |
template< class T, class Alloc, class Pred >
std::list<T, Alloc>::size_type
erase_if( std::list<T, Alloc>& c, Pred pred );
|
(2) | (since C++20) |
1) Erases all elements that compare equal to
value from the container. 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. Equivalent to return c.remove_if(pred);.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 |
Return value
The number of erased elements.
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 algorithm (1) |
Example
Run this code
#include <complex>
#include <numeric>
#include <print>
#include <list>
template<typename T>
struct std::formatter<std::complex<T>, char>
{
template<class ParseContext>
constexpr ParseContext::iterator parse(ParseContext& ctx)
{
return ctx.begin();
}
template<class FmtContext>
FmtContext::iterator format(const auto& s, FmtContext& ctx) const
{
auto out{std::format("({},{})", s.real(), s.imag())};
return std::ranges::copy(std::move(out), ctx.out()).out;
}
};
int main()
{
std::list<char> cnt(10);
std::iota(cnt.begin(), cnt.end(), '0');
std::println("Initially, cnt = {}", cnt);
std::erase(cnt, '3');
std::println("After erase '3', cnt = {}", cnt);
auto erased = std::erase_if(cnt, [](char x) { return (x - '0') % 2 == 0; });
std::println("After erase all even numbers, cnt = {}", cnt);
std::println("Erased even numbers: {}", erased);
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
std::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
|