std::map<Key,T,Compare,Allocator>::swap
void swap( map& other ); |
(until C++17) | |
void swap( map& other ) noexcept(/* see below */); |
(since C++17) |
Exchanges the contents of the container with those of other. Does not invoke any move, copy, or swap operations on individual elements.
All iterators and references remain valid. The past-the-end iterator is invalidated.
The Compare objects must be Swappable, and they are exchanged using unqualified call to non-member swap.
| If |
(since C++11) |
Parameters
| other | - | container to exchange the contents with |
Return value
(none).
Exceptions
| Any exception thrown by the swap of the |
(until C++17) |
noexcept specification:
noexcept(std::allocator_traits<Allocator>::is_always_equal::value
|
(since C++17) |
Complexity
Constant.
Example
#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.
}
Output:
──────── 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
See also
specializes the std::swap algorithm (function template) |
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