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

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

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

If std:: allocator_traits < Allocator > ::
propagate_on_container_swap :: value &&
get_allocator ( ) == s. get_allocator ( ) is false , the behavior is undefined.

(since C++11)

Parameters

other - string to exchange the contents with

Complexity

Constant.

Exceptions

No exception is thrown.

(until C++11)

No exception is thrown, unless the behavior is undefined.

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

Run this code 
#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
LWG 2151
( P1148R0 ) 		C++11 no exception was thrown in the case
of unequal non-propagating allocators 		the behavior is
undefined in this case

See also

swaps the values of two objects
(function template)
swaps two ranges of elements
(function template)
swaps the contents
(public member function of std::basic_string_view<CharT,Traits> )
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