caution

Note, this article is not finished! You can help by editing this doc page.

Overview

Simplified

template< class CharT, /* ... */ >
class basic_string;

Detailed

Regular

template<
		class CharT,
		class Traits	= std::char_traits<CharT>,
		class Allocator	= std::allocator<CharT>
	>
class basic_string;

Polymorphic (since C++17)

namespace pmr {
    template< class CharT, class Traits = std::char_traits<CharT> >
    using basic_string = std::basic_string<CharT, Traits,
                                            std::polymorphic_allocator<CharT>>;
}

A class that is used to store and manipulate sequence of characters.

Memory

The elements of a string are stored contiguously in memory. This means that a pointer to an element of a string may be passed to any function that expects a pointer to an element of an array of characters.

Aliases

Type std::string is in fact an alias to: std::basic_string<char>.

Available std::basic_string aliases

pub	std::string	std::basic_string<char>
pub	std::wstring	std::basic_string<wchar_t>
pub	std::u8string (since C++20)	std::basic_string<char8_t>
pub	std::u16string (since C++11)	std::basic_string<char16_t>
pub	std::u32string (since C++11)	std::basic_string<char32_t>
pub	std::pmr::string (since C++17)	std::pmr::basic_string<char>
pub	std::pmr::wstring (since C++17)	std::pmr::basic_string<wchar_t>
pub	std::pmr::u8string (since C++20)	std::pmr::basic_string<char8_t>
pub	std::pmr::u16string (since C++17)	std::pmr::basic_string<char16_t>
pub	std::pmr::u32string (since C++17)	std::pmr::basic_string<char32_t>

Technical details

Technical definition of a string

The class template basic_string stores and manipulates sequences of char-like objects, which are non-array objects of trivial standard-layout type. 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. Traits::char_type and CharT must name the same type; otherwise the program is ill-formed

.

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() ), or, equivalently, a pointer to s[0] can be passed to functions that expect a pointer to the first element of a null-terminated (since C++11) CharT[] array.

std::basic_string

Defined in

string

Template parameters

pub	CharT	A character type.
pub	Traits	Traits class specifying the operations on the character type.
pub	Allocator	Allocator type used to allocate internal storage.

Type names

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

Member functions

pub	(constructors)	Constructs a basic_string.
pub	(destructor)	Destroys the string, deallocating internal storage if used.
pub	operator=	Assigns values to the string.
pub	assign	Assigns characters to the string.
pub	get_allocator	Returns the associated allocator.

Element access

pub	at	Accesses the specified character with bounds checking.
pub	operator[]	Accesses the specified character.
pub	front (since C++11)	Returns the first character.
pub	back (since C++11)	Returns the last character.
pub	data	Returns a pointer to the first character of a string.
pub	c_str	Returns a non-modifiable standard C character array version of the string.
pub	operator basic_string_view (since C++17)	Returns a non-modifiable string_view into the entire string.

Iterators

pub	begin cbegin (since C++11)	Returns an iterator/const_iterator to the beginning.
pub	end cend (since C++11)	Returns an iterator/const_iterator to the end.
pub	rbegin crbegin (since C++11)	Returns an reverse iterator/const_iterator to the beginning.
pub	rend crend (since C++11)	Returns an reverse iterator/const_iterator to the end.

Capacity

pub	empty	Returns true if the string is empty, otherwise false.
pub	size length	Returns the number of characters.
pub	max_size	Returns the maximum number of characters.
pub	reserve	Reserves storage
pub	capacity	Returns the number of characters that can be held in currently allocated storage
pub	shrink_to_fit (since C++11)	Reduces memory usage by freeing unused memory.

Operations

pub	clear	Clears the contents.
pub	insert	Inserts characters.
pub	erase	Removes characters.
pub	push_back	Appends a character to the end.
pub	pop_back (since C++11)	Removes the last character.
pub	append	Appends characters to the end.
pub	operator+=	Appends characters to the end.
pub	compare	Compares two strings.
pub	starts_with (since C++20)	Checks if the string starts with the given prefix.
pub	ends_with (since C++20)	Checks if the string ends with the given suffix.
pub	contains (since C++23)	Checks if the string contains the given substring or character.
pub	replace	Replaces specified portion of a string.
pub	substr	Returns a substring.
pub	copy	Copies characters.
pub	resize	Changes the number of characters stored.
pub	resize_and_overwrite (since C++23)	Changes the number of characters stored and possibly overwrites indeterminate contents via user-provided operation.
pub	swap	Swaps the contents.

Search

pub	find	Find characters in the string.
pub	rfind	Find the last occurrence of a substring.
pub	find_first_of	Find first occurrence of characters.
pub	find_first_not_of	Find first absence of characters.
pub	find_last_of	Find last occurrence of characters.
pub	find_last_not_of	Find last absence of characters.

Constants

pubstaticconstexpr

npos

A special value. The exact meaning depends on the context.

Non-member functions

pub	operator+	Concatenates two strings or a string and a char.
pub	operator== operator!=  (removed in C++20) operator<  (removed in C++20) operator>  (removed in C++20) operator<=  (removed in C++20) operator>=  (removed in C++20) operator<=>	Lexicographically compares two strings.
pub	std::swap (std::basic_string)	An overload for a std::swap algorithm.
pub	erase (std::basic_string) erase_if (std::basic_string)	Overloads for std::erase/std::erase_if algorithms.

Input/output

pub	operator<< operator>>	Performs stream input and output on strings.
pub	getline	Read data from an I/O stream into a string.

Numeric conversions

pub	stoi stol stoll	Converts a string to a signed integer.
pub	stoui stoul stoull	Converts a string to an unsigned integer.
pub	stof stod stold	Converts a string to a floating point value.
pub	to_string	Converts an integral or floating point value to std::string.
pub	to_wstring	Converts an integral or floating point value to std::wstring.

Literals

Defined in namespace std::literals::string_literals

pub

operator ""s

Converts a character array literal to std::string.

Helper classes

pub

std::hash<std::string>  (since C++11) std::hash<std::u8string>  (since C++20) std::hash<std::u16string>  (since C++11) std::hash<std::u32string>  (since C++11) std::hash<std::wstring>  (since C++11) std::hash<std::pmr::string>  (since C++17) std::hash<std::pmr::u8string>  (since C++20) std::hash<std::pmr::u16string>  (since C++17) std::hash<std::pmr::u32string>  (since C++17) std::hash<std::pmr::wstring>  (since C++17)

Specializations for std::hash to support string hashing.

Deduction guides (since C++17)

Click to expand

Deduction guides

// (1)
template< class InputIt, class Alloc = std::allocator<
                         typename std::iterator_traits<InputIt>::value_type> >
basic_string( InputIt, InputIt, Alloc = Alloc() )
  -> basic_string<typename std::iterator_traits<InputIt>::value_type,
                std::char_traits<typename std::iterator_traits<InputIt>::value_type>,
                Alloc>;

(1) allows deduction from a iterator range

// (2)
template< class CharT,
          class Traits,
          class Alloc = std::allocator<CharT> >
explicit basic_string( std::basic_string_view<CharT, Traits>, const Alloc& = Alloc() )
  -> basic_string<CharT, Traits, Alloc>;

// (3)
template< class CharT,
          class Traits,
          class Alloc = std::allocator<CharT>> >
basic_string( std::basic_string_view<CharT, Traits>, typename /*see below*/::size_type,
              typename /*see below*/::size_type, const Alloc& = Alloc() )
    -> basic_string<CharT, Traits, Alloc>;

(2) and (3) allow deduction from a std::basic_string_view<CharT, Traits>

The size_type parameter type refers to the size_type member type of the type deduced by the deduction guide.

Overload resolution

In order for any of the deduction guides to participate in overload resolution, the folllowing requirements must be met:

• for (1), InputIt satisfies LegacyInputIterator
• for (1 - 3), Alloc satisfies Allocator

note

The extent to which the library determines that a type does not satisfy LegacyInputIterator is unspecified, except that as a minimum:

• Integral types do not qualify as input iterators.

Likewise, the extent to which it determines that a type does not satisfy Allocator is unspecified, except that as a minimum:

• The member type Alloc::value_type must exist.
• The expression std::declval<Alloc&>().allocate(std::size_t{}) must be well-formed when treated as an unevaluated operand.

Examples

Basic manipulation

Creating and printing a simple string

#include <iostream>
#include <string>

int main()
{
	std::string s = "World";
	std::cout << "Hello, " << s << "!" << std::endl;
}

Result

Hello, World!

Concatenating strings

#include <iostream>
#include <string>

int main()
{
	std::string a = "Hello, ";
	std::string b = "World!";
	std::string c = a + b;
	std::cout << c;
}

Result

Hello, World!

Splitting a string

#include <iostream>
#include <string>

int main()
{
	// Split by the comma.
	//                    v
	std::string a = "Hello, World!";
	size_t pos = a.find(',');

	std::string hello = a.substr(0, pos);
	// 1 for a comma, and 1 for a space before "World"
	std::string world = a.substr(pos + 1 + 1);

	std::cout << hello << '\n' << world;
}

Result

Hello
World!

Conversions

Convert a string to int

#include <iostream>
#include <string>

int main()
{
	std::string numberInString = "8314";

	// Note: stoi can throw exception if failed!
	int number = std::stoi(numberInString);
	std::cout << "Number: " << number;
}

Result

Number: 8314

Convert string to float

#include <iostream>
#include <string>

int main()
{
	std::string numberInString = "3.141";

	// Note: stof can throw exception if failed!
	float number = std::stof(numberInString);
	std::cout << "Number: " << number;
}

Result

Number: 3.141

Convert numbers to std::string

Convert string to float

#include <iostream>
#include <string>

int main()
{
	std::string numberInString = "3.141";

	// Note: stof can throw exception if failed!
	float number = std::stof(numberInString);
	std::cout << "Number: " << number;
}

Possible output

s1: 123
s2: 456.200012
s3: 3.141590

tip

If you want a custom formatting, use std::stringstream, or a non-standard library fmtlib.