std::basic_string<CharT,Traits,Allocator>::swap
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basic_string::swap
(C++20)
(C++20)
(C++23)
(C++20)(C++20)
(until C++20)(until C++20)(until C++20)(until C++20)(until C++20)(C++20)
(C++11)(C++11)(C++11)
(C++11)(C++11)
(C++14)
(C++11)
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).
[edit] Parameters
other
-
string to exchange the contents with
[edit] Complexity
Constant.
[edit] 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:
(since C++17)noexcept(std::allocator_traits <Allocator>::propagate_on_container_swap::value ||
std::allocator_traits <Allocator>::is_always_equal::value)
std::allocator_traits <Allocator>::is_always_equal::value)
[edit] 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
[edit] 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 |