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String view class reference

Overview

Simplified

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

Detailed

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

A class that is used as a lightweight view over a sequence of characters.

Memory

important

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Aliases

Type std::string_view is in fact an alias to: std::basic_string_view<char>.

Available std::basic_string_view aliases

pub	std::string_view	std::basic_string_view<char>
pub	std::wstring_view	std::basic_string_view<wchar_t>
pub	std::u8string_view (since C++20)	std::basic_string_view<char8_t>
pub	std::u16string_view (since C++11)	std::basic_string_view<char16_t>
pub	std::u32string_view (since C++11)	std::basic_string_view<char32_t>

Technical details

Technical definition of a string view

The class template basic_string_view describes an object that can refer to a constant contiguous sequence of char-like objects with the first element of the sequence at position zero.

A typical implementation holds only two members: a pointer to constant CharT and a size.

Every specialization of std::basic_string_view is a TriviallyCopyable type.  (since C++11)

Named requirements

std::basic_string_view meets the requirements of:

• TriviallyCopyable (since C++23)
  • note

    Specializations of std::basic_string_view are already trivially copyable types in all existing implementations, even before the formal requirement introduced in C++23.

Feature testing macros

important

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std::string_view

Defined in

string_view

Template parameters

pub	CharT	Character type
pub	Traits	CharTraits class specifying the operations on the character type. important Like for std::basic_string, Traits::char_type must name the same type as CharT or the program is ill-formed .

Type names

pub	traits_type	Traits
pub	value_type	CharT
pub	pointer	CharT*
pub	const_pointer	const CharT*
pub	reference	CharT
pub	const_reference	const CharT&
pub	const_iterator	implementation-defined constant LegacyInputIterator, ConstexprIterator  (since C++20) and LegacyContiguousIterator  (until C++20) contiguous_iterator  (since C++20) whose value_type is CharT
pub	const_reverse_iterator	std::reverse_iterator<const_iterator>
pub	reverse_iterator	const_reverse_iterator
pub	size_type	std::size_t
pub	difference_type	std::ptrdiff_t

Iterators

iterator and const_iterator are the same type because string views are views into constant character sequences.

All requirements on the iterator types of a Container applies to the iterator and const_iterator types of std::basic_string_view as well.

Member functions

pub	(constructors)	Constructs a string view.
pub	(destructor)	Destroys the string view.
pub	operator=	Assigns values to the string string view.

Element access

pub	at	Accesses the specified character with bounds checking.
pub	operator[]	Accesses the specified character.
pub	front	Returns the first character.
pub	back	Returns the last character.
pub	data	Returns a pointer to the first character of a view.

Iterators

pub	begin cbegin	Returns an iterator/const_iterator to the beginning.
pub	end cend	Returns an iterator/const_iterator to the end.
pub	rbegin crbegin	Returns a reverse iterator/const_iterator to the beginning.
pub	rend crend	Returns a reverse iterator/const_iterator to the end.

Capacity

pub	empty	Returns true if the view is empty, otherwise false.
pub	size length	Returns the number of characters.
pub	max_size	Returns the maximum number of characters.

Modifiers

pub	remove_prefix	Shrinks the view by moving its start forward.
pub	remove_suffix	Shrinks the view by moving its end backward.
pub	swap	Swaps the contents.

Operations

pub	copy	Copies characters.
pub	substr	Returns a substring.
pub	compare	Compares two views.
pub	starts_with (since C++20)	Checks if the view starts with the given prefix.
pub	ends_with (since C++20)	Checks if the view ends with the given suffix.
pub	contains (since C++23)	Checks if the view contains the given substring or character.
pub	find	Find the first occurrence of a substring.
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== 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 string views.

Input/output

pub

operator<<

Performs stream output on views.

Literals

Defined in namespace std::literals::string_view_literals

pub

operator ""sv

Creates a string view out of a character literal.

Helper classes

pub

std::hash<std::string_view>  (since C++11) std::hash<std::wstring_view>  (since C++11) std::hash<std::u8string_view>  (since C++20) std::hash<std::u16string_view>  (since C++11) std::hash<std::u32string_view>  (since C++11)

Specializations for std::hash to support string view hashing.

Specializations

since C++20

template<class CharT, class Traits>
inline constexpr bool ranges::enable_borrowed_range<std::basic_string_view<CharT, Traits>> = true;

This specialization of ranges::enable_borrowed_range makes basic_string_view satisfy borrowed_range.

since C++20

template<class CharT, class Traits>
inline constexpr bool ranges::enable_view<std::basic_string_view<CharT, Traits>> = true;

This specialization of ranges::enable_view makes basic_string_view satisfy view.

Deduction guides (since C++20)

Click to expand

// (1)
template<class It, class End>
basic_string_view(It, End) -> basic_string_view<std::iter_value_t<It>>;

(1) allows deduction from an iterator-sentinel pair.

// (2)
template<class R>
basic_string_view(R&&) -> basic_string_view<ranges::range_value_t<R>>;

(2) allows the character type to be deduced from an arbitrary range.

Overload resolution

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

• for (1), It satisfies contiguous_iterator and End satisfies sized_sentinel_for for It
• for (2), R satisfies contiguous_range

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