Difference between revisions of "cpp/string/basic string/operator="
From cppreference.com
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{{dcl | num=6 | since=c++17 | 1= | {{dcl | num=6 | since=c++17 | 1= | ||
template<class T> | template<class T> | ||
| − | basic_string& operator=( const T& t); | + | basic_string& operator=( const T& t ); |
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{{dcl end}} | {{dcl end}} | ||
Revision as of 08:08, 18 March 2018
| basic_string& operator=( const basic_string& str ); |
(1) | |
| basic_string& operator=( basic_string&& str ); |
(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 participates in overload resolution only if std::is_convertible_v<const StringViewLike&,
std::basic_string_view<CharT, Traits>> is true and std::is_convertible_v<const StringViewLike&, const CharT*> is false.
std::basic_string_view<CharT, Traits>> is true and std::is_convertible_v<const StringViewLike&, const CharT*> is false.
Contents |
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) |
Example
| This section is incomplete Reason: no example |
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 |
See also
constructs a basic_string (public member function) | |
| assign characters to a string (public member function) |
