# std::basic_string<CharT,Traits,Allocator>::operator=

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< cpp‎ | string‎ | basic string

basic_string& operator=( const basic_string& str ); | (1) |
| (2) |
basic_string& operator=( basic_string&& str ); |  | (since C++11) (until C++17)
basic_string& operator=( basic_string&& str ) noexcept(/* see below */); |  | (since C++17)
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. `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.
3) Replaces the contents with those of null-terminated character string pointed to by `s` as if by assign(s, Traits::length(s)).
4) Replaces the contents with character `ch` as if by assign( std::addressof (ch), 1)
5) Replaces the contents with those of the initializer list `ilist` as if by assign(ilist.begin(), ilist.size())
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
ilist | - | 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 `ilist`

### Exceptions

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

### Example

| This section is incomplete Reason: no example

### See also

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

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