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

 

C++

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Feature test macros (C++20)

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Concepts library (C++20)

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Metaprogramming library (C++11)

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Ranges library (C++20)

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Technical specifications

Symbols index

External libraries

 

Strings library

Classes

basic_string

basic_string_view (C++17)

char_traits

 

std::basic_string

Member functions basic_string::basic_string basic_string::~basic_string basic_string::operator= basic_string::assign basic_string::assign_range (C++23)   basic_string::get_allocator Element access basic_string::at basic_string::operator[] basic_string::front (DR*) basic_string::back (DR*) basic_string::data basic_string::c_str basic_string::operator  basic_string_view (C++17) Iterators basic_string::beginbasic_string::cbegin (C++11) basic_string::endbasic_string::cend (C++11) basic_string::rbeginbasic_string::crbegin (C++11) basic_string::rendbasic_string::crend (C++11) Search basic_string::find basic_string::rfind basic_string::find_first_of basic_string::find_first_not_of basic_string::find_last_of basic_string::find_last_not_of

Modifiers basic_string::clear basic_string::insert basic_string::insert_range (C++23) basic_string::erase basic_string::push_back basic_string::pop_back (DR*) basic_string::append basic_string::append_range (C++23) basic_string::operator+= basic_string::replace basic_string::replace_with_range (C++23) basic_string::copy basic_string::resize basic_string::resize_and_overwrite (C++23)  basic_string::swap Capacity basic_string::empty basic_string::sizebasic_string::length basic_string::max_size basic_string::reserve basic_string::capacity basic_string::shrink_to_fit (DR*) Operations basic_string::compare basic_string::starts_with (C++20) basic_string::ends_with (C++20) basic_string::contains (C++23) basic_string::substr

Constants basic_string::npos Non-member functions operator+ swap(std::basic_string) erase(std::basic_string)erase_if(std::basic_string) (C++20)(C++20) I/O operator<<operator>> getline Comparison operator==operator!=operator<operator>operator<=operator>=operator<=> (until C++20)(until C++20)(until C++20)(until C++20)(until C++20)(C++20) Numeric conversions stoistolstoll (C++11)(C++11)(C++11) stoulstoull (C++11)(C++11)  stofstodstold (C++11)(C++11)(C++11) to_string (C++11) to_wstring (C++11) Literals operator""s (C++14) Helper classes hash<std::basic_string> (C++11) Deduction guides (C++17)

 

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_type>::propagate_on_container_swap::value is true, then the allocators are exchanged using an unqualified call to non-member swap. Otherwise, they are not swapped (and if get_allocator() != other.get_allocator(), 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

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