std::map swap() 方法

自 C++17 起

// Non const version only
void swap( map& other ) noexcept(/* see below */);

C++17 之前

// Non const version only
void swap( map& other );

将容器的内容与 `other` 的内容进行交换。不调用单个元素的任何移动、复制或交换操作。

失效

past-the-end 迭代器失效。

所有其他迭代器和引用保持有效。

Compare 对象必须是Swappable，并且它们通过对非成员 swap 的非限定调用进行交换。

参数

• other - 要交换内容的容器

返回值

(无)

异常

自 C++17 起

noexcept 规范

noexcept(std::allocator_traits<Allocator>::is_always_equal::value
&& std::is_nothrow_swappable<Compare>::value)

C++17 之前

由 Compare 对象的交换抛出的任何异常。

复杂度

常数 - O(1)。

示例

Main.cpp

#include <iostream>
#include <string>
#include <utility>
#include <map>
 
// print out a std::pair
template <class Os, class U, class V>
Os& operator<<(Os& os, const std::pair<U, V>& p) {
    return os << p.first << ":" << p.second;
}
 
// print out a container
template <class Os, class Co>
Os& operator<<(Os& os, const Co& co) {
    os << "{";
    for (auto const& i : co) { os << ' ' << i; }
    return os << " }\n";
}
 
int main()
{
    std::map<std::string, std::string>
        m1 { {"γ", "gamma"}, {"β", "beta"}, {"α", "alpha"}, {"γ", "gamma"}, },
        m2 { {"ε", "epsilon"}, {"δ", "delta"}, {"ε", "epsilon"} };
 
    const auto& ref = *(m1.begin());
    const auto iter = std::next(m1.cbegin());
 
    std::cout << "──────── before swap ────────\n"
              << "m1: " << m1 << "m2: " << m2 << "ref: " << ref
              << "\niter: " << *iter << '\n';
 
    m1.swap(m2);
 
    std::cout << "──────── after swap ────────\n"
              << "m1: " << m1 << "m2: " << m2 << "ref: " << ref
              << "\niter: " << *iter << '\n';
 
    // Note that every iterator referring to an element in one container before
    // the swap refers to the same element in the other container after the swap.
    // Same is true for references.
}

输出

──────── before swap ────────
m1: { α:alpha β:beta γ:gamma }
m2: { δ:delta ε:epsilon }
ref: α:alpha
iter: β:beta
──────── after swap ────────
m1: { δ:delta ε:epsilon }
m2: { α:alpha β:beta γ:gamma }
ref: α:alpha
iter: β:beta