std::basic_string

 

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Strings library

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Classes

basic_string

basic_string_view (C++17)

char_traits

 

std::basic_string

Member functions basic_string::basic_string basic_string::~basic_string basic_string::operator= basic_string::assign basic_string::assign_range (C++23) basic_string::get_allocator Element access basic_string::at basic_string::operator[] basic_string::front (DR*) basic_string::back (DR*) basic_string::data basic_string::c_str basic_string::operator  basic_string_view (C++17) Iterators basic_string::beginbasic_string::cbegin (C++11) basic_string::endbasic_string::cend (C++11) basic_string::rbeginbasic_string::crbegin (C++11) basic_string::rendbasic_string::crend (C++11) Capacity basic_string::empty basic_string::sizebasic_string::length basic_string::max_size basic_string::reserve basic_string::capacity basic_string::shrink_to_fit (DR*) Modifiers basic_string::clear basic_string::insert basic_string::insert_range (C++23) basic_string::erase basic_string::push_back basic_string::pop_back (DR*) basic_string::append basic_string::append_range (C++23) basic_string::operator+= basic_string::replace basic_string::replace_with_range (C++23) basic_string::copy basic_string::resize basic_string::resize_and_overwrite (C++23)   basic_string::swap

Search basic_string::find basic_string::rfind basic_string::find_first_of basic_string::find_first_not_of basic_string::find_last_of basic_string::find_last_not_of Operations basic_string::compare basic_string::starts_with (C++20) basic_string::ends_with (C++20) basic_string::contains (C++23) basic_string::substr Constants basic_string::npos Non-member functions operator+ swap(std::basic_string) erase(std::basic_string)erase_if(std::basic_string) (C++20)(C++20) I/O operator<<operator>> getline Comparison operator==operator!=operator<operator>operator<=operator>=operator<=> (until C++20)(until C++20)(until C++20)(until C++20)(until C++20)(C++20) Numeric conversions stoistolstoll (C++11)(C++11)(C++11) stoulstoull (C++11)(C++11) stofstodstold (C++11)(C++11)(C++11) to_string (C++11) to_wstring (C++11) Literals operator""s (C++14) Helper classes hash<std::basic_string> (C++11) Deduction guides (C++17)

 

Defined in header <string>
template<     class CharT,     class Traits = std::char_traits<CharT>,     class Allocator = std::allocator<CharT> > class basic_string;	(1)
namespace pmr { template<     class CharT,     class Traits = std::char_traits<CharT> > using basic_string =     std::basic_string<CharT, Traits, std::pmr::polymorphic_allocator<CharT>>; }	(2)	(since C++17)

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. However, std::string objects generally cannot be constexpr, because any dynamically allocated storage must be released in the same evaluation of constant expression.

(since C++20)

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

Nested types

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

Data members

constexpr size_type npos [static]

the special value size_type(-1), its exact meaning depends on the context

Member functions

(constructor)	constructs a basic_string (public member function)
(destructor)	destroys the string, deallocating internal storage if used (public member function)
operator=	assigns values to the string (public member function)
assign	assign characters to a string (public member function)
assign_range (C++23)	assign a range of characters to a string (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 (DR*)	accesses the first character (public member function)
back (DR*)	accesses the last character (public member function)
data	returns a pointer to the first character of a string (public member function)
c_str	returns a non-modifiable standard C character array version of the string (public member function)
operator basic_string_view (C++17)	returns a non-modifiable basic_string_view into the entire string (public member function)
Iterators
begincbegin (C++11)	returns an iterator to the beginning (public member function)
endcend (C++11)	returns an iterator to the end (public member function)
rbegincrbegin (C++11)	returns a reverse iterator to the beginning (public member function)
rendcrend (C++11)	returns a reverse iterator to the end (public member function)
Capacity
empty	checks whether the string is empty (public member function)
sizelength	returns the number of characters (public member function)
max_size	returns the maximum number of characters (public member function)
reserve	reserves storage (public member function)
capacity	returns the number of characters that can be held in currently allocated storage (public member function)
shrink_to_fit (DR*)	reduces memory usage by freeing unused memory (public member function)
Modifiers
clear	clears the contents (public member function)
insert	inserts characters (public member function)
insert_range (C++23)	inserts a range of characters (public member function)
erase	removes characters (public member function)
push_back	appends a character to the end (public member function)
pop_back (DR*)	removes the last character (public member function)
append	appends characters to the end (public member function)
append_range (C++23)	appends a range of characters to the end (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 (C++23)	replaces specified portion of a string with a range of characters (public member function)
copy	copies characters (public member function)
resize	changes the number of characters stored (public member function)
resize_and_overwrite (C++23)	changes the number of characters stored and possibly overwrites indeterminate contents via user-provided 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 (C++20)	checks if the string starts with the given prefix (public member function)
ends_with (C++20)	checks if the string ends with the given suffix (public member function)
contains (C++23)	checks if the string contains the given substring or character (public member function)
substr	returns a substring (public member function)

Non-member functions

operator+	concatenates two strings, a string and a char, or a string and string_view (function template)
operator==operator!=operator<operator>operator<=operator>=operator<=> (removed in C++20)(removed in C++20)(removed in C++20)(removed in C++20)(removed in C++20)(C++20)	lexicographically compares two strings (function template)
std::swap(std::basic_string)	specializes the std::swap algorithm (function template)
erase(std::basic_string)erase_if(std::basic_string) (C++20)	erases all elements satisfying specific criteria (function template)
Input/output
operator<<operator>>	performs stream input and output on strings (function template)
getline	read data from an I/O stream into a string (function template)
Numeric conversions
stoistolstoll (C++11)(C++11)(C++11)	converts a string to a signed integer (function)
stoulstoull (C++11)(C++11)	converts a string to an unsigned integer (function)
stofstodstold (C++11)(C++11)(C++11)	converts a string to a floating point value (function)
to_string (C++11)	converts an integral or floating-point value to string (function)
to_wstring (C++11)	converts an integral or floating-point value to wstring (function)

Literals

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

Helper classes

std::hash<std::basic_string> (C++11)

hash support for strings (class template specialization)

Iterator invalidation

References, pointers, and iterators referring to the elements of a basic_string may be invalidated by any standard library function taking a reference to non-const basic_string as an argument, such as std::getline, std::swap, or operator>>, and by calling non-const member functions, except operator[], at, data, front, back, begin, rbegin, end, and rend.

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
__cpp_lib_containers_ranges	202202L	(C++23)	Member functions for 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
LWG 530	C++98	contiguity of the storage for elements of basic_string was accidently made not required by LWG259	required again
LWG 2861	C++98	value_type was Traits::char_type	changed to CharT
LWG 2994 (P1148R0)	C++98	the behavior is undefined if any of Traits::char_type and Allocator::char_type is different from CharT	the program is ill-formed in this case

See also

basic_string_view (C++17)

read-only string view (class template)

External links

C++ string handling