erase_if在哪里？

Question

我有一个容器,想根据谓词擦除元素.erase_if听起来很熟悉,但我在C++中找不到它.名称是什么,它定义在哪里？我想在VS10中使用lambda.

Answer 1

您可能正在寻找std::remove_if,例如:

vec.erase(std::remove_if(vec.begin(), vec.end(), predicate), vec.end());

Answer 2

它在Library Fundamentals v2中，不久之后在C ++ 20中。

Answer 3

我猜你正在考虑remove_if哪个需要一个谓词来确定是否应该删除元素。

remove_if返回一个迭代器，指向容器中要删除的元素的开头。要实际删除它们，您需要使用erase：

container.erase(remove_if(container.start(), container.end(), pred), container.end())

或者你错误地回忆了copy_if算法？不知何故被排除在标准之外，但在Effective STL 中编写并实施。

Answer 4

MSVC 尚未std::erase_if从P1209R0实现 C++20 ，因此，作为一种解决方法，您可以将特定容器的实现从该论文某处复制到您的代码中。GCC 9.1 和 Clang 9.0 已经有了它。

namespace std {

// for std::string
template <class charT, class traits, class A, class Predicate>
void erase_if(basic_string<charT, traits, A>& c, Predicate pred) {
    c.erase(remove_if(c.begin(), c.end(), pred), c.end());
}

// for std::deque
template <class T, class A, class Predicate>
void erase_if(deque<T, A>& c, Predicate pred) {
    c.erase(remove_if(c.begin(), c.end(), pred), c.end());
}

// for std::vector
template <class T, class A, class Predicate>
void erase_if(vector<T, A>& c, Predicate pred) {
    c.erase(remove_if(c.begin(), c.end(), pred), c.end());
}

// for std::list
template <class T, class A, class Predicate>
void erase_if(list<T, A>& c, Predicate pred) {
    c.remove_if(pred);
}

// for std::forward_list
template <class T, class A, class Predicate>
void erase_if(forward_list<T, A>& c, Predicate pred) {
    c.remove_if(pred);
}

// for std::map
template <class K, class T, class C, class A, class Predicate>
void erase_if(map<K, T, C, A>& c, Predicate pred) {
    for (auto i = c.begin(), last = c.end(); i != last; )
        if (pred(*i))
            i = c.erase(i);
        else
            ++i;
}

// for std::multimap
template <class K, class T, class C, class A, class Predicate>
void erase_if(multimap<K, T, C, A>& c, Predicate pred) {
    for (auto i = c.begin(), last = c.end(); i != last; )
        if (pred(*i))
            i = c.erase(i);
        else
            ++i;
}

// for std::set
template <class K, class C, class A, class Predicate>
void erase_if(set<K, C, A>& c, Predicate pred) {
    for (auto i = c.begin(), last = c.end(); i != last; )
        if (pred(*i))
            i = c.erase(i);
        else
            ++i;
}

// for std::multiset
template <class K, class C, class A, class Predicate>
void erase_if(multiset<K, C, A>& c, Predicate pred) {
    for (auto i = c.begin(), last = c.end(); i != last; )
        if (pred(*i))
            i = c.erase(i);
        else
            ++i;
}

// for std::unordered_map
template <class K, class T, class H, class P, class A, class Predicate>
void erase_if(unordered_map<K, T, H, P, A>& c, Predicate pred) {
    for (auto i = c.begin(), last = c.end(); i != last; )
        if (pred(*i))
            i = c.erase(i);
        else
            ++i;
}

// for std::unordered_multimap
template <class K, class T, class H, class P, class A, class Predicate>
void erase_if(unordered_multimap<K, T, H, P, A>& c, Predicate pred) {
    for (auto i = c.begin(), last = c.end(); i != last; )
        if (pred(*i))
            i = c.erase(i);
        else
            ++i;
}

// for std::unordered_set
template <class K, class H, class P, class A, class Predicate>
void erase_if(unordered_set<K, H, P, A>& c, Predicate pred) {
    for (auto i = c.begin(), last = c.end(); i != last; )
        if (pred(*i))
            i = c.erase(i);
        else
            ++i;
}

// for std::unordered_multiset
template <class K, class H, class P, class A, class Predicate>
void erase_if(unordered_multiset<K, H, P, A>& c, Predicate pred) {
    for (auto i = c.begin(), last = c.end(); i != last; )
        if (pred(*i))
            i = c.erase(i);
        else
            ++i;
}

} // namespace std