basic_string&operator=(constbasic_string&str); (1)(constexpr since C++20)basic_string&operator=(basic_string&&str)noexcept(/* see below */); (2)(since C++11)
(constexpr since C++20)basic_string&operator=(constCharT*s); (3)(constexpr since C++20)basic_string&operator=(CharTch); (4)(constexpr since C++20)basic_string&operator=(std::initializer_list<CharT>ilist); (5)(since C++11)
(constexpr since C++20)template<classStringViewLike>basic_string&operator=(constStringViewLike&t); (6)(since C++17)
(constexpr since C++20)basic_string&operator=(std::nullptr_t)=delete; (7) (since C++23)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
's move assignment semantics.
Unlike other sequence container move assignments, references, pointers, and iterators to elements of 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 participates in overload resolution only if std::is_convertible_v<constStringViewLike&,std::basic_string_view<CharT,Traits>> is true and std::is_convertible_v<constStringViewLike&,constCharT*> is false.
7)std::basic_string cannot be assigned from nullptr.
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 -
to initialize the string with t - object convertible to
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.
6) Linear in size of t.
Exceptions
2)
specification:
noexcept(std::allocator_traits<Allocator>::propagate_on_container_move_assignment::value||std::allocator_traits<Allocator>::is_always_equal::value)If the operation would cause
to exceed
, throws
.
If an exception is thrown for any reason, this function has no effect (
strong exception safety guarantee
).
Example
Run this code
#include<iomanip>#include<iostream>#include<string>intmain(){std::stringstr1;std::stringstr2{"alpha"};// (1) operator=(const basic_string&);str1=str2;std::cout<<std::quoted(str1)<<' '// "alpha"<<std::quoted(str2)<<'\n';// "alpha"// (2) operator=(basic_string&&);str1=std::move(str2);std::cout<<std::quoted(str1)<<' '// "alpha"<<std::quoted(str2)<<'\n';// "" or "alpha" (unspecified)// (3) operator=(const CharT*);str1="beta";std::cout<<std::quoted(str1)<<'\n';// "beta"// (4) operator=(CharT);str1='!';std::cout<<std::quoted(str1)<<'\n';// "!"// (5) operator=(std::initializer_list<CharT>);str1={'g','a','m','m','a'};std::cout<<std::quoted(str1)<<'\n';// "gamma"// (6) operator=(const T&);str1=35U;// equivalent to str1 = static_cast<char>(35U);std::cout<<std::quoted(str1)<<'\n';// "#" (ASCII = 35)}Possible output:
"alpha" "alpha" "alpha" "" "beta" "!" "gamma" "#" Defect reports
The following behavior-changing defect reports were applied retroactively to previously published C++ standards.
DR Applied to Behavior as published Correct behavior
C++98 there was no exception safety guarantee added strong exception safety guarantee
C++11 the move assignment operator did not follow
's semantic requirement follows
C++17 overload (
) caused 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)
assigns a view
(public member function of std::basic_string_view<CharT,Traits>)