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std::swap(std::basic_string)

Defined in header <string> 
template< class CharT, class Traits, class Alloc >
void swap( std::basic_string<CharT, Traits, Alloc>& lhs,
           std::basic_string<CharT, Traits, Alloc>& rhs );
 (until C++17) 
template< class CharT, class Traits, class Alloc >
void swap( std::basic_string<CharT, Traits, Alloc>& lhs,
           std::basic_string<CharT, Traits, Alloc>& rhs ) noexcept(/* see below */);
 (since C++17)
(until C++20)		 
template< class CharT, class Traits, class Alloc >
constexpr void
    swap( std::basic_string<CharT, Traits, Alloc>& lhs,
          std::basic_string<CharT, Traits, Alloc>& rhs ) noexcept(/* see below */);
 (since C++20)

Specializes the std::swap algorithm for std::basic_string. Swaps the contents of lhs and rhs.

Equivalent to lhs.swap(rhs).

Parameters

lhs, rhs - strings whose contents to swap

Return value

(none)

Complexity

Constant.

Exceptions

noexcept specification:
noexcept(noexcept(lhs.swap(rhs)))
(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";
 
    std::swap(a, 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 2064 C++11 non-member swap was noexcept and inconsistent with member swap noexcept removed

See also

swaps the contents
(public member function)

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https://en.cppreference.com/w/cpp/string/basic_string/swap2