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std::string assign() method

// (1) Non const version only
constexpr basic_string& assign( size_type count, CharT ch );

// (2) Non const version only
constexpr basic_string& assign( const basic_string& str );

// (3) Non const version only
constexpr basic_string& assign( const basic_string& str,
                      size_type pos, size_type count = npos);

// (4) Non const version only
constexpr basic_string& assign( basic_string&& str ) noexcept(/* see below */);

// (5) Non const version only
constexpr basic_string& assign( const CharT* s, size_type count );

// (6) Non const version only
constexpr basic_string& assign( const CharT* s );

// (7) Non const version only
template< class InputIt >
constexpr basic_string& assign( InputIt first, InputIt last );

// (8) Non const version only
constexpr basic_string& assign( std::initializer_list<CharT> ilist );

// (9) Non const version only
template < class StringViewLike >
constexpr basic_string& assign( const StringViewLike& t );

// (10) Non const version only
template < class StringViewLike >
constexpr basic_string& assign( const StringViewLike& t,
                      size_type pos, size_type count = npos);

Replaces the contents of the string.

  • (1) Replaces the contents with count copies of character ch.

  • (2) Replaces the contents with a copy of str. Equivalent to *this = str;.
    In particular, allocator propagation may take place. (od C++11)

  • (3) Replaces the contents with a substring [ pos, pos + count ) of str.
    If the requested substring lasts past the end of the string, or if count == npos, the resulting substring is [ pos, str.size() ). If pos > str.size(), std::out_of_range is thrown.

  • (4) Replaces the contents with those of str using move semantics. Equivalent to *this = std::move(str). In particular, allocator propagation may take place.

  • (5) Replaces the contents with copies of the characters in the range [ s, s+count ). This range can contain null characters.

  • (6) Replaces the contents with those of null-terminated character string pointed to by s.
    The length of the string is determined by the first null character using Traits::length(s).

  • (7) Replaces the contents with copies of the characters in the range [ first, last ). This overload does not participate in overload resolution if InputIt does not satisfy LegacyInputIterator.  (od C++11)

  • (8) Replaces the contents with those of the initializer list ilist.

  • (9) 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 sv, as if by assign(sv.data(), sv.size()).

    Overload Resolution

    This overload participates in overload resolution only if std::is_convertible_v<const StringViewLike&, std::basic_string_view<CharT, Traits>> is true and std::is_convertible_v<const StringViewLike&, const CharT*> is false.

  • (10) Implicitly converts t to a string view sv as if by std::basic_string_view<CharT, Traits> sv = t;, then replaces the contents with the characters from the subview [ pos, pos + count ) of sv.
    If the requested subview lasts past the end of sv, or if count == npos, the resulting subview is [ pos, sv.size() ). If pos > sv.size(), std::out_of_range is thrown.

    Overload Resolution

    This overload participates in overload resolution only if std::is_convertible_v<const StringViewLike&, std::basic_string_view<CharT, Traits>> is true and std::is_convertible_v<const StringViewLike&, const CharT*> is false.

Parameters​

  • 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
  • ilist - std::initializer_list to initialize the characters of the string with
  • t - object (convertible to std::basic_string_view) to initialize the characters of the string with

Type requirements​

Return value​

*this

Complexity​

  • (1) Linear in count - O(count).
  • (2) Linear in size of str - O(str.size()).
  • (3) Linear in count - O(count).
  • (4)
    Constant - O(1). If alloc is given and alloc != other.get_allocator(), then linear in size - O(size()).
  • (5) Linear in count - O(count).
  • (6) Linear in size of s - O(s.size()).
  • (7) Linear in distance [ first, last ) - O(std::distance(first, last)).
  • (8) Linear in size of ilist - O(ilist.size()).

Exceptions​

  • (4) noexcept specification:
noexcept(std::allocator_traits<Allocator>::propagate_on_container_move_assignment::value
 || std::allocator_traits<Allocator>::is_always_equal::value)

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).  (od C++11)

Example​

Main.cpp
#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"
}
Output
====
Exemplary == Exemplary
Exemplar
C++ by example
C-style
C-style
C-style string
C-style
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