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std::basic_string::operator=

basic_string& operator=( const basic_string& str );	(1)
basic_string& operator=( basic_string&& str ) noexcept(/* see below */);	(2)	(since C++11)
basic_string& operator=( const CharT* s );	(3)
basic_string& operator=( CharT ch );	(4)
basic_string& operator=( std::initializer_list<CharT> ilist );	(5)	(since C++11)
template<class T> basic_string& operator=( const T& t );	(6)	(since C++17)

Replaces the contents of the string.

1) Replaces the contents with a copy of str. If *this and str are the same object, this function has no effect.

2) Replaces the contents with those of str using move semantics. Leaves str in valid, but unspecified state. If *this and str are the same object, the function has no effect. (until C++17)

2) Replaces the contents with those of str using move semantics. str is in a valid but unspecified state afterwards. If std::allocator_traits<Allocator>::propagate_on_container_move_assignment() is true, the target allocator is replaced by a copy of the source allocator. If it is false and the source and the target allocators do not compare equal, the target cannot take ownership of the source memory and must assign each character individually, allocating additional memory using its own allocator as needed. Unlike other container move assignments, references, pointers, and iterators to str may be invalidated. (since C++17)

3) Replaces the contents with those of null-terminated character string pointed to by s as if by *this = basic_string(s), which involves a call to Traits::length(s).

4) Replaces the contents with character ch as if by *this = basic_string(1,c)

5) Replaces the contents with those of the initializer list ilist as if by *this = basic_string(ilist)

6) Implicitly converts t to a string view sv as if by std::basic_string_view<CharT, Traits> sv = t;, then replaces the contents with those of the sv as if by assign(sv). This overload only participates in overload resolution if std::is_convertible_v<const T&, std::basic_string_view<CharT, Traits>> is true and std::is_convertible_v<const T&, const CharT*> is false.

Parameters

ch	-	value to initialize characters of the string with
str	-	string to be used as source to initialize the string with
s	-	pointer to a null-terminated character string to use as source to initialize the string with
init	-	`std::initializer_list` to initialize the string with
t	-	object convertible to `std::basic_string_view` to initialize the string with

Return value

*this.

Complexity

1) linear in size of str

2) linear in the size of this (formally, each CharT has to be destroyed). If allocators do not compare equal and do not propagate, then also linear in the size of str (copy must be made)

3) linear in size of s

4) constant.

5) linear in size of init

Exceptions

2) `noexcept` specification: `noexcept`	(since C++11) (until C++17)
2) `noexcept` specification: `noexcept(std::allocator_traits<Allocator>::propagate_on_container_move_assignment::value \|\| std::allocator_traits<Allocator>::is_always_equal::value)`	(since C++17)

If the operation would result in size() > max_size(), throws std::length_error.

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

(since C++11)

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 2063	C++11	non-normative note stated that swap is a valid implementation of move assignment	corrected to support allocators
LWG 2946	C++17	`string_view` overload causes ambiguity in some cases	avoided by making it a template

(constructor)	constructs a `basic_string` (public member function)
assign	assign characters to a string (public member function)