std::basic_string::assign

basic_string& assign( size_type count, CharT ch );	(1)
basic_string& assign( const basic_string& str );	(2)
	(3)
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)
basic_string& assign( basic_string&& str );	(4)	(since C++11)
basic_string& assign( const CharT* s, size_type count );	(5)
basic_string& assign( const CharT* s );	(6)
template< class InputIt > basic_string& assign( InputIt first, InputIt last );	(7)
basic_string& assign( std::initializer_list<CharT> ilist );	(8)	(since C++11)
basic_string& assign( std::basic_string_view<CharT, Traits> sv);	(9)	(since C++17)
template < class T > basic_string& assign( const T& t, size_type pos, size_type count = npos);	(10)	(since C++17)

替换字符串的内容。

1%29将内容替换为count字符副本ch...

2%29将内容替换为str...

3%29用子字符串替换内容。[pos, pos+count)成str如果请求的子字符串持续到字符串的末尾，或者count == npos，生成的子字符串是[pos, str.size()).如果pos > str.size()，，，std::out_of_range被扔了。

4%29将内容替换为str使用移动语义。相当于*this = std::move(str)...

5%29将内容替换为第一个count所指向的字符串字符s...s可以包含空字符。

6%29将内容替换为s字符串的长度由第一个空字符决定。

7%29将内容替换为范围内字符的副本。[first, last)此重载不参与重载解决方案。InputIt不满意InputIterator.%28自C++11%29

8%29将内容替换为初始化程序列表的内容。ilist...

9%29将内容替换为字符串视图的内容。sv，好像assign(sv.data(), sv.size())

10%29名皈依者t到字符串视图sv好像std::basic_string_view<CharT, Traits> sv = t;，然后将内容替换为子视图中的字符。[pos, pos+count)成sv如果所请求的子视图持续到sv，或者如果count == npos，生成的子视图是[pos, sv.size()).如果pos > sv.size()，，，std::out_of_range被扔了。此重载只参与在下列情况下的重载解决方案：std::is_convertible_v<const T&,std::basic_string_view<CharT, Traits>>是true和std::is_convertible_v<const T&, const CharT*>是false...

参数

count	-	size of the resulting string
pos	-	index of the first character to take
ch	-	value to initialize characters of the string with
first, last	-	range to copy the characters from
str	-	string to be used as source to initialize the characters with
s	-	pointer to a character string to use as source to initialize the string with
init	-	std::initializer_list to initialize the characters of the string with
sv	-	std::basic_string_view to initialize the characters of the string with
t	-	object (convertible to std::basic_string_view) to initialize the characters of the string with

类型要求

-输入必须符合输入器的要求。

返回值

*this...

复杂性

1%29线性count

2%29线性str

3%29线性count

4%29常数。如果alloc被赋予和alloc != other.get_allocator()，然后是线性的。

5%29线性count

6%29线性s

7%29直线之间的距离first和last

8%29线性init

例外

如果出于任何原因引发异常，则此函数没有效果%28强异常保证%29。%28自C++11%29。

如果手术会导致size() > max_size()，抛std::length_error...

4) noexcept specification: noexcept	(since C++11)(until C++17)
4) noexcept specification: noexcept(std::allocator_traits<Allocator>::propagate_on_container_move_assignment::value \|\| std::allocator_traits<Allocator>::is_always_equal::value)	(since C++17)

例

二次

#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(basic_string const& str)
  s.assign(c);
  std::cout << c << "==" << s <<'\n'; // "Exemplary == Exemplary"
 
  // assign(basic_string const& 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(charT const* s, size_type count)
  s.assign("C-style string", 7);
  std::cout << s << '\n'; // "C-style"
 
  // assign(charT const* 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"
}

二次

产出：

二次

====
Exemplary==Exemplary
Exemplar
C++ by example
C-style
C-style
C-style string
C-style

二次

缺陷报告

以下行为更改缺陷报告追溯应用于先前发布的C++标准。

DR	Applied to	Behavior as published	Correct behavior
LWG 2063	C++11	non-normative note stated that swap is a valid implementation of move-assign	corrected to require move assignment

另见

(constructor)	constructs a basic_string (public member function)
operator=	assigns values to the string (public member function)

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最后更新于：2017-12-18