std::basic_string<CharT,Traits,Allocator>::assign
From cppreference.com
< cpp | string | basic string
C++
Feature test macros (C++20)
Concepts library (C++20)
Metaprogramming library (C++11)
Ranges library (C++20)
Filesystem library (C++17)
Concurrency support library (C++11)
Execution control library (C++26)
std::basic_string
Literals Helper classes Deduction guides (C++17)
basic_string::assign
(C++23)
(DR*)
(DR*)
(C++23)
(DR*)
(C++23)
(C++23)
(C++20)
(C++20)
(C++23)
(C++20)(C++20)
(until C++20)(until C++20)(until C++20)(until C++20)(until C++20)(C++20)
(C++11)(C++11)(C++11)
(C++11)(C++11)
(C++14)
(C++11)
basic_string& assign( const basic_string& str );
(1)
(constexpr since C++20)
basic_string& assign( basic_string&& str ) noexcept(/* see below */);
(2)
(since C++11) (constexpr since C++20)
basic_string& assign( size_type count, CharT ch );
(3)
(constexpr since C++20)
basic_string& assign( const CharT* s, size_type count );
(4)
(constexpr since C++20)
basic_string& assign( const CharT* s );
(5)
(constexpr since C++20)
template< class SV >
basic_string& assign( const SV& t );
(6)
(since C++17) basic_string& assign( const SV& t );
(constexpr since C++20)
template< class SV >
(7)
(since C++17) basic_string& assign( const SV& t,
(constexpr since C++20)
(8)
basic_string& assign( const basic_string& str,
size_type pos, size_type count );
(until C++14)
size_type pos, size_type count );
basic_string& assign( const basic_string& str,
size_type pos, size_type count = npos);
(since C++14) size_type pos, size_type count = npos);
(constexpr since C++20)
template< class InputIt >
basic_string& assign( InputIt first, InputIt last );
(9)
(constexpr since C++20)
basic_string& assign( InputIt first, InputIt last );
basic_string& assign( std::initializer_list <CharT> ilist );
(10)
(since C++11) (constexpr since C++20)
Replaces the contents of the string.
1) Equivalent to return *this = str;.
2) Equivalent to return *this = std::move(str);.
3) Replaces the contents with count copies of character ch.
Equivalent to clear(); resize(n, c); return *this;.
4) Replaces the contents with copies of the characters in the range
[s, s + count). If
[s, s + count) is not a valid range, the behavior is undefined.5) Equivalent to return assign(s, Traits::length(s));.
6,7) Replaces the contents with characters in a string view sv constructed from t.
These overloads participate in overload resolution only if all following conditions are satisfied:
- std::is_convertible_v <const SV&, std::basic_string_view <CharT, Traits>> is true.
- std::is_convertible_v <const SV&, const CharT*> is false.
6) Equivalent to std::basic_string_view <CharT, Traits> sv = t;
return assign(sv.data(), sv.size());.
return assign(sv.data(), sv.size());.
7) Equivalent to std::basic_string_view <CharT, Traits> sv = t;
return assign(sv.substr(pos, count));.
return assign(sv.substr(pos, count));.
8) Replaces the contents with characters in str.
Equivalent to return assign(std::basic_string_view <CharT, Traits>
(str).substr(pos, count));.
(since C++20)(str).substr(pos, count));.
9) Equivalent to return assign(basic_string(first, last, get_allocator()));.
This overload participates in overload resolution only if InputIt satisfies the requirements of LegacyInputIterator.
10) Equivalent to return assign(ilist.begin(), ilist.size());.
[edit] Parameters
str
-
string to be used as source to initialize the characters with
count
-
size of the resulting string
ch
-
value to initialize characters of the string with
s
-
pointer to a character string to use as source to initialize the string with
t
-
object (convertible to std::basic_string_view ) to initialize the characters of the string with
pos
-
index of the first character to take
first, last
-
range to copy the characters from
ilist
-
std::initializer_list to initialize the characters of the string with
[edit] Return value
*this
[edit] Exceptions
2)
noexcept specification:
noexcept(std::allocator_traits <Allocator>::
propagate_on_container_move_assignment::value ||
If the operation would cause size() to exceed max_size() , throws std::length_error .
If an exception is thrown for any reason, this function has no effect (strong exception safety guarantee).
[edit] Example
Run this code
#include <iostream> #include <iterator> #include <string> int main() { std::string s; // assign(size_type count, CharT ch) s.assign(4, '='); std::cout << s << '\n'; // "====" std::string const c("Exemplary"); // assign(const basic_string& str) s.assign(c); std::cout << c << " == " << s << '\n'; // "Exemplary == Exemplary" // assign(const basic_string& str, size_type pos, size_type count) s.assign(c, 0, c.length() - 1); std::cout << s << '\n'; // "Exemplar"; // assign(basic_string&& str) s.assign(std::string ("C++ by ") + "example"); std::cout << s << '\n'; // "C++ by example" // assign(const CharT* s, size_type count) s.assign("C-style string", 7); std::cout << s << '\n'; // "C-style" // assign(const CharT* s) s.assign("C-style0円string"); std::cout << s << '\n'; // "C-style" char mutable_c_str[] = "C-style string"; // assign(InputIt first, InputIt last) s.assign(std::begin (mutable_c_str), std::end (mutable_c_str) - 1); std::cout << s << '\n'; // "C-style string" // assign(std::initializer_list<CharT> ilist) s.assign({'C', '-', 's', 't', 'y', 'l', 'e'}); std::cout << s << '\n'; // "C-style" }
Output:
==== Exemplary == Exemplary Exemplar C++ by example C-style C-style C-style string C-style
[edit] 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 847 | C++98 | there was no exception safety guarantee | added strong exception safety guarantee |
| LWG 2063 | C++11 | non-normative note stated that overload (2) can be implemented by swapping |
corrected to require move assignment |
| LWG 2250 | C++98 | the behavior of overload (8) was undefined if pos > str.size() is true |
always throws an exception in this case |
| LWG 2579 | C++98 | overload (1) and the copy assignment operator had different effects |
they have the same effect |
| LWG 2946 | C++17 | overload (6) caused ambiguity in some cases | avoided by making it a template |