std::erase,...f(std::list)(3)

🎀 std::erase,...f(std::list)(3) 🎀

Okay so welcome to the C++ Standard Libary manual page for std::erase and std::erase_if on std::list — yes, that’s the manual name folded in right here, bestie, instead of a boring copied header line. We’re gonna make this make sense together. 💅

🌸 NAME 🌸

std::erase,std::erase_if(std::list) — std::erase,std::erase_if(std::list)

🦋 Synopsis 🦋

Defined in header <list>.

First erase overload, bestie:

template< class T, class Alloc, class U >
std::list<T, Alloc>::size_type
erase( std::list<T, Alloc>& c, const U& value );

• Tags: (since C++20), (until C++26).

Second erase overload, now with the default value type glow-up:

template< class T, class Alloc, class U = T >
std::list<T, Alloc>::size_type
erase( std::list<T, Alloc>& c, const U& value );

• Tags: (1), (since C++26).

And the erase_if girlie:

template< class T, class Alloc, class Pred >
std::list<T, Alloc>::size_type
erase_if( std::list<T, Alloc>& c, Pred pred );

• Tags: (2), (since C++20).

What they do, fr fr:

1. Erases all elements that compare equal to value from the container. Equivalent to return c.remove_if([&](auto& elem) { 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 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). Ngl, that constraint is strict, so read it twice. 😭

💖 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 📊

• Feature-test macro: __cpp_lib_algorithm_default_value_type — Value: 202403 — Std: C++26 — Feature: List-initialization for algorithm (1)

🧚 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 << "{ ";
    for (const auto& x : c)
        std::cout << 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) }

👑 See also 👑

• remove — removes elements satisfying specific criteria.
• remove_if — (function template).
• remove — removes elements satisfying specific criteria.
• remove_if — (public member function).

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That’s the whole vibe check, bestie 💖. Source/version: http://cppreference.com; date: 2024.06.10; page: std::erase,...f(std::list)(3). Now go erase those elements like the main character you are ✨.