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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. (since 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.  (since 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).  (since 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
This article originates from this CppReference page. It was likely altered for improvements or editors' preference. Click "Edit this page" to see all changes made to this document.
Hover to see the original license.

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. (since 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.  (since 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).  (since 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
This article originates from this CppReference page. It was likely altered for improvements or editors' preference. Click "Edit this page" to see all changes made to this document.
Hover to see the original license.