std::basic_string(3)

NAME
std::basic_string - std::basic_string

Synopsis
   Defined in header <string>
   template<
       class CharT,
       class Traits = std::char_traits<CharT>, (1)
       class Allocator = std::allocator<CharT>
   > class basic_string;
   namespace pmr {
   template<
       class CharT,
       class Traits = std::char_traits<CharT> (2) (since C++17)
   > using basic_string =
       std::basic_string<CharT, Traits,
   std::pmr::polymorphic_allocator<CharT>>;
   }
   The class template basic_string stores and manipulates sequences of character-like
   objects, which are non-array objects of TrivialType and StandardLayoutType. The
   class is dependent neither on the character type nor on the nature of operations on
   that type. The definitions of the operations are supplied via the Traits template
   parameter - a specialization of std::char_traits or a compatible traits class.
   The elements of a basic_string are stored contiguously, that is, for a basic_string
   s, &*(s.begin() + n) == &*s.begin() + n for any n in [0, s.size())
   , and *(s.begin() + s.size()) has value CharT() (a null terminator)
   (since C++11); or, equivalently, a pointer to s[0] can be passed to functions that
   expect a pointer to the first element of
   an array
   (until C++11)
   a null-terminated array
   (since C++11) of CharT.
   std::basic_string satisfies the requirements of AllocatorAwareContainer (except that
   customized construct/destroy are not used for construction/destruction of elements),
   SequenceContainer
   and ContiguousContainer
   (since C++17).
   If any of Traits::char_type and Allocator::char_type is different from CharT, the
   program is ill-formed.
   Member functions of std::basic_string are constexpr: it is possible to
   create and use std::string objects in the evaluation of a constant
   expression.
                        (since C++20)
   However, std::string objects generally cannot be constexpr, because
   any dynamically allocated storage must be released in the same
   evaluation of constant expression.
   Several typedefs for common character types are provided:
   Defined in header <string>
   Type Definition
   std::string std::basic_string<char>
   std::wstring std::basic_string<wchar_t>
   std::u8string (C++20) std::basic_string<char8_t>
   std::u16string (C++11) std::basic_string<char16_t>
   std::u32string (C++11) std::basic_string<char32_t>
   std::pmr::string (C++17) std::pmr::basic_string<char>
   std::pmr::wstring (C++17) std::pmr::basic_string<wchar_t>
   std::pmr::u8string (C++20) std::pmr::basic_string<char8_t>
   std::pmr::u16string (C++17) std::pmr::basic_string<char16_t>
   std::pmr::u32string (C++17) std::pmr::basic_string<char32_t>

Template parameters
   CharT - character type
   Traits - traits class specifying the operations on the character type
   Allocator - Allocator type used to allocate internal storage

Member types
   Member type Definition
   traits_type Traits
   value_type CharT
   allocator_type Allocator
                        Allocator::size_type (until C++11)
   size_type std::allocator_traits<Allocator>::size_type (since C++11)
                        Allocator::difference_type (until
                        C++11)
   difference_type std::allocator_traits<Allocator>::difference_type (since
                        C++11)
   reference value_type&
   const_reference const value_type&
                        Allocator::pointer (until C++11)
   pointer std::allocator_traits<Allocator>::pointer (since C++11)
                        Allocator::const_pointer (until C++11)
   const_pointer std::allocator_traits<Allocator>::const_pointer (since C++11)
                        LegacyRandomAccessIterator and (until C++20)
                        LegacyContiguousIterator to value_type
                        LegacyRandomAccessIterator,
   iterator contiguous_iterator, and ConstexprIterator to (since C++20)
                        value_type
                        LegacyRandomAccessIterator and (until C++20)
                        LegacyContiguousIterator to const value_type
                        LegacyRandomAccessIterator,
   const_iterator contiguous_iterator, and ConstexprIterator to (since C++20)
                        const value_type
   reverse_iterator std::reverse_iterator<iterator>
   const_reverse_iterator std::reverse_iterator<const_iterator>

Member functions
   constructor constructs a basic_string
                        (public member function)
                        destroys the string, deallocating internal storage if
   destructor used
                        (public member function)
   operator= assigns values to the string
                        (public member function)
   assign assign characters to a string
                        (public member function)
   assign_range assign a range of characters to a string
   (C++23) (public member function)
   get_allocator returns the associated allocator
                        (public member function)

Element access
   at accesses the specified character with bounds checking
                        (public member function)
   operator[] accesses the specified character
                        (public member function)
   front accesses the first character
   (DR*) (public member function)
   back accesses the last character
   (DR*) (public member function)
   data returns a pointer to the first character of a string
                        (public member function)
                        returns a non-modifiable standard C character array
   c_str version of the string
                        (public member function)
   operator basic_string_view returns a non-modifiable string_view into the entire
   (C++17) string
                        (public member function)

Iterators
   begin returns an iterator to the beginning
   cbegin (public member function)
   (C++11)
   end returns an iterator to the end
   cend (public member function)
   (C++11)
   rbegin returns a reverse iterator to the beginning
   crbegin (public member function)
   (C++11)
   rend returns a reverse iterator to the end
   crend (public member function)
   (C++11)

Capacity
   empty checks whether the string is empty
                        (public member function)
   size returns the number of characters
   length (public member function)
   max_size returns the maximum number of characters
                        (public member function)
   reserve reserves storage
                        (public member function)
                        returns the number of characters that can be held in
   capacity currently allocated storage
                        (public member function)
   shrink_to_fit reduces memory usage by freeing unused memory
   (DR*) (public member function)

Modifiers
   clear clears the contents
                        (public member function)
   insert inserts characters
                        (public member function)
   insert_range inserts a range of characters
   (C++23) (public member function)
   erase removes characters
                        (public member function)
   push_back appends a character to the end
                        (public member function)
   pop_back removes the last character
   (DR*) (public member function)
   append appends characters to the end
                        (public member function)
   append_range appends a range of characters to the end
   (C++23) (public member function)
   operator+= appends characters to the end
                        (public member function)
   replace replaces specified portion of a string
                        (public member function)
   replace_with_range replaces specified portion of a string with a range of
   (C++23) characters
                        (public member function)
   copy copies characters
                        (public member function)
   resize changes the number of characters stored
                        (public member function)
                        changes the number of characters stored and possibly
   resize_and_overwrite overwrites indeterminate contents via user-provided
   (C++23) operation
                        (public member function)
   swap swaps the contents
                        (public member function)

Search
   find finds the first occurrence of the given substring
                        (public member function)
   rfind find the last occurrence of a substring
                        (public member function)
   find_first_of find first occurrence of characters
                        (public member function)
   find_first_not_of find first absence of characters
                        (public member function)
   find_last_of find last occurrence of characters
                        (public member function)
   find_last_not_of find last absence of characters
                        (public member function)

Operations
   compare compares two strings
                        (public member function)
   starts_with checks if the string starts with the given prefix
   (C++20) (public member function)
   ends_with checks if the string ends with the given suffix
   (C++20) (public member function)
   contains checks if the string contains the given substring or
   (C++23) character
                        (public member function)
   substr returns a substring
                        (public member function)

Constants
   npos special value. The exact meaning depends on the context
   [static] (public static member constant)

Non-member functions
   operator+ concatenates two strings or a string and a char
                        (function template)
   operator==
   operator!=
   operator<
   operator>
   operator<=
   operator>= lexicographically compares two strings
   operator<=> (function template)
   (removed in C++20)
   (removed in C++20)
   (removed in C++20)
   (removed in C++20)
   (removed in C++20)
   (C++20)
   std::swap(std::basic_string) specializes the std::swap algorithm
                        (function template)
   erase(std::basic_string) erases all elements satisfying specific criteria
   erase_if(std::basic_string) (function template)
   (C++20)

Input/output
   operator<< performs stream input and output on strings
   operator>> (function template)
   getline read data from an I/O stream into a string
                        (function template)

Numeric conversions
   stoi
   stol
   stoll converts a string to a signed integer
   (C++11) (function)
   (C++11)
   (C++11)
   stoul
   stoull converts a string to an unsigned integer
   (C++11) (function)
   (C++11)
   stof
   stod
   stold converts a string to a floating point value
   (C++11) (function)
   (C++11)
   (C++11)
   to_string converts an integral or floating-point value to string
   (C++11) (function)
   to_wstring converts an integral or floating-point value to wstring
   (C++11) (function)

Literals
   Defined in inline namespace std::literals::string_literals
   operator""s converts a character array literal to basic_string
   (C++14) (function)

Helper classes
   std::hash<std::basic_string> hash support for strings
   (C++11) (class template specialization)
   Deduction guides (since C++17)

Notes
   Although it is required that customized construct or destroy is used when
   constructing or destroying elements of std::basic_string until C++23, all
   implementations only used the default mechanism. The requirement is corrected by
   P1072R10 to match existing practice.
            Feature-test macro Value Std Feature
   __cpp_lib_string_udls 201304L (C++14) User-defined literals for
                        string types
   __cpp_lib_starts_ends_with 201711L (C++20) starts_with, ends_with
   __cpp_lib_constexpr_string 201907L (C++20) Constexpr for
                        std::basic_string
   __cpp_lib_char8_t 201907L (C++20) std::u8string
   __cpp_lib_erase_if 202002L (C++20) erase, erase_if
   __cpp_lib_string_contains 202011L (C++23) contains
   __cpp_lib_string_resize_and_overwrite 202110L (C++23) resize_and_overwrite
                        Member functions for
   __cpp_lib_containers_ranges 202202L (C++23) construction, insertion, and
                        replacement that accept
                        container compatible range

Example
// Run this code
 #include <iostream>
 #include <string>
 int main()
 {
     using namespace std::literals;
     // Creating a string from const char*
     std::string str1 = "hello";
     // Creating a string using string literal
     auto str2 = "world"s;
     // Concatenating strings
     std::string str3 = str1 + " " + str2;
     // Print out the result
     std::cout << str3 << '\n';
     std::string::size_type pos = str3.find(" ");
     str1 = str3.substr(pos + 1); // the part after the space
     str2 = str3.substr(0, pos); // the part till the space
     std::cout << str1 << ' ' << str2 << '\n';
     // Accessing an element using subscript operator[]
     std::cout << str1[0] << '\n';
     str1[0] = 'W';
     std::cout << str1 << '\n';
 }

Output:
 hello world
 world hello
 w
 World
   Defect reports
   The following behavior-changing defect reports were applied retroactively to
   previously published C++ standards.
      DR Applied to Behavior as published Correct behavior
                        contiguity of the storage for elements of
   LWG 530 C++98 basic_string required again
                        was accidently made not required by LWG259
                        the behavior is undefined if any of the program is
   LWG 2994 C++98 Traits::char_type^[1] ill-formed in this
   (P1148R0) and Allocator::char_type is different from case
                        CharT
    1. ↑ The Traits::char_type case is fixed in P1148R0.

See also
   basic_string_view read-only string view
   (C++17) (class template)

External links
   C++ string handling

Hidden category:
     * Pages with unreviewed LWG DR marker