std::basic_string<CharT,Traits,Allocator>::assign
From cppreference.com
< cpp | string | basic string
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) (constexpr since C++20) |
template
<
class SV >
basic_string& assign( const SV& t, |
(7) | (since C++17) (constexpr since C++20) |
(8) | ||
basic_string& assign(
const basic_string& str,
size_type pos, size_type count ) ; |
(until C++14) | |
basic_string& assign(
const basic_string& str,
size_type pos, size_type count = npos) ; |
(since C++14) (constexpr since C++20) |
|
template
<
class InputIt >
basic_string& assign( InputIt first, InputIt last ) ; |
(9) | (constexpr since C++20) |
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
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) |
9) Equivalent to
return assign(basic_string(first, last, get_allocator(
)
)
)
;
.
This overload participates in overload resolution only if |
(since C++11) |
10) Equivalent to
return assign(ilist.begin
(
), ilist.size
(
)
)
;
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 |
Return value
*this
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).
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-style\0string"); 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
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 |
See also
(C++23)
|
assign a range of characters to a string (public member function) |
constructs a basic_string (public member function) |
|
assigns values to the string (public member function) |