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std::basic_string<CharT,Traits,Allocator>::swap

void swap( basic_string& other );		(until C++17)
void swap( basic_string& other ) noexcept(/* see below */);		(since C++17) (until C++20)
constexpr void swap( basic_string& other ) noexcept(/* see below */);		(since C++20)

Exchanges the contents of the string with those of other. All iterators and references may be invalidated.

The behavior is undefined if Allocator does not propagate on swap and the allocators of *this and other are unequal.

(since C++11)

Parameters

other

string to exchange the contents with

Return value

(none).

Complexity

Constant.

Exceptions

No exception is thrown.

(until C++11)

Exceptions can only be thrown in the case where the behavior is undefined (see above).

If an exception is thrown for any reason, this function has no effect (strong exception safety guarantee).

(since C++11)

noexcept specification:

noexcept(std::allocator_traits<Allocator>::propagate_on_container_swap::value ||
 std::allocator_traits<Allocator>::is_always_equal::value)

(since C++17)

Example

#include <iostream>
#include <string>
 
int main() 
{
    std::string a = "AAA";
    std::string b = "BBBB";
 
    std::cout << "Before swap:\n"
                 "a = " << a << "\n"
                 "b = " << b << "\n\n";
 
    a.swap(b);
 
    std::cout << "After swap:\n"
                 "a = " << a << "\n"
                 "b = " << b << '\n';
}

Output:

Before swap:
a = AAA
b = BBBB
 
After swap:
a = BBBB
b = AAA

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 403	C++98	`swap()` might throw an exception	no exception is thrown
LWG 535	C++98	swapping strings did not preserve the character orders	orders are also preserved

swap	swaps the values of two objects (function template)
swap_ranges	swaps two ranges of elements (function template)
swap (C++17)	swaps the contents (public member function of `std::basic_string_view<CharT,Traits>`)