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

 

C++

Language

Standard Library Headers

Freestanding and hosted implementations

Named requirements

Language support library

Concepts library (C++20)

Diagnostics library

Utilities library

Strings library

Containers library

Iterators library

Ranges library (C++20)

Algorithms library

Numerics library

Input/output library

Localizations library

Regular expressions library (C++11)

Atomic operations library (C++11)

Thread support library (C++11)

Filesystem library (C++17)

Technical Specifications

 

Strings library

Null-terminated strings

Byte strings

Multibyte strings

Wide strings

Classes

basic_string

basic_string_view (C++17)

char_traits

 

std::basic_string

Member functions basic_string::basic_string basic_string::operator= basic_string::assign basic_string::get_allocator Element access basic_string::at basic_string::operator[] basic_string::front (C++11) basic_string::back (C++11) 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) Capacity basic_string::empty basic_string::sizebasic_string::length basic_string::max_size basic_string::reserve basic_string::capacity basic_string::shrink_to_fit (C++11)

Operations basic_string::clear basic_string::insert basic_string::erase basic_string::push_back basic_string::pop_back (C++11) basic_string::append basic_string::operator+= basic_string::compare basic_string::starts_with (C++20) basic_string::ends_with (C++20) basic_string::replace basic_string::substr basic_string::copy basic_string::resize basic_string::swap 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 Constants basic_string::npos

Non-member functions operator+ swap(std::basic_string) operator""s (C++14) 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 conversion (C++11) stoistolstoll stoulstoull stofstodstold to_string to_wstring Helper classes hash<std::string>hash<std::wstring>hash<std::u32string>hash<std::u16string>hash<std::u8string> (C++11)(C++11)(C++11)(C++11)(C++20) hash<std::pmr::string>hash<std::pmr::wstring>hash<std::pmr::u32string>hash<std::pmr::u16string>hash<std::pmr::u8string> (C++20)(C++20)(C++20)(C++20)(C++20) Deduction guides(C++17)

 

	(1)
basic_string& operator=( const basic_string& str );			(until C++20)
constexpr basic_string& operator=( const basic_string& str );			(since C++20)
		(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) (until C++20)
constexpr basic_string&     operator=( basic_string&& str ) noexcept(/* see below */);				(since C++20)
			(3)
basic_string& operator=( const CharT* s );					(until C++20)
constexpr basic_string& operator=( const CharT* s );					(since C++20)
				(4)
basic_string& operator=( CharT ch );						(until C++20)
constexpr basic_string& operator=( CharT ch );						(since C++20)
					(5)
basic_string& operator=( std::initializer_list<CharT> ilist );							(since C++11) (until C++20)
constexpr basic_string& operator=( std::initializer_list<CharT> ilist );							(since C++20)
						(6)
template<class T> basic_string& operator=( const T& t );								(since C++17) (until C++20)
template<class T> constexpr basic_string& operator=( const T& t );								(since C++20)

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

See also

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