NAME¶

std::basic_string_view::basic_string_view - std::basic_string_view::basic_string_view

Synopsis¶

constexpr basic_string_view() noexcept; (1) (since C++17)
constexpr basic_string_view( const basic_string_view& other )
noexcept (2) (since C++17)
= default;
constexpr basic_string_view( const CharT* s, size_type count ); (3) (since C++17)
constexpr basic_string_view( const CharT* s ); (4) (since C++17)
template< class It, class End > (5) (since C++20)
constexpr basic_string_view( It first, End last );
template< class R > (6) (since C++23)
explicit constexpr basic_string_view( R&& r );
constexpr basic_string_view( std::nullptr_t ) = delete; (7) (since C++23)

1) Default constructor. Constructs an empty basic_string_view. After construction,
data() is equal to nullptr, and size() is equal to 0.
2) Copy constructor. Constructs a view of the same content as other. After
construction, data() is equal to other.data(), and size() is equal to other.size().
3) Constructs a view of the first count characters of the character array starting
with the element pointed by s. s can contain null characters. The behavior is
undefined if [s, s+count) is not a valid range (even though the constructor may not
access any of the elements of this range). After construction, data() is equal to s,
and size() is equal to count.
4) Constructs a view of the null-terminated character string pointed to by s, not
including the terminating null character. The length of the view is determined as if
by Traits::length(s). The behavior is undefined if [s, s+Traits::length(s)) is not a
valid range. After construction, data() is equal to s, and size() is equal to
Traits::length(s).
5) Constructs a basic_string_view over the range [first, last). The behavior is
undefined if [first, last) is not a valid range, if It does not actually model
contiguous_iterator, or if End does not actually model sized_sentinel_for for It.
After construction, data() is equal to std::to_address(first), and size() is equal
to (last - first).

This overload participates in overload resolution only if

* It satisfies contiguous_iterator,
* End satisfies sized_sentinel_for for It,
* std::iter_value_t<It> and CharT are the same type, and
* End is not convertible to std::size_t.

6) Constructs a basic_string_view over the range r. After construction, data() is
equal to ranges::data(r), and size() is equal to ranges::size(r).

This overload participates in overload resolution only if

* std::remove_cvref_t<R> is not the same type as basic_string_view,
* R models contiguous_range and sized_range,
* ranges::range_value_t<R> and CharT are the same type,
* R is not convertible to const CharT*,
* let d be an lvalue of type std::remove_cvref_t<R>, d.operator
::std::basic_string_view<CharT, Traits>() is not a valid expression,
and
* if qualified-id std::remove_reference_t<R>::traits_type is valid and
denotes a type, it is same as Traits.

7) basic_string_view cannot be constructed from nullptr.

Parameters¶

other - another view to initialize the view with
s - pointer to a character array or a C string to initialize the view with
count - number of characters to include in the view
first - iterator to the first character of the sequence
last - iterator past the last character of the sequence or another sentinel
r - a contiguous range that contains the sequence

Complexity¶

1-3,5-6) constant
4) linear in length of s

Example¶

// Run this code

#include <array>
#include <iomanip>
#include <iostream>
#include <string>
#include <string_view>

int main()
{
std::string cppstr = "Foo";
std::string_view cppstr_v(cppstr); // overload (2), after
// std::string::operator string_view
std::cout << "1) cppstr_v: " << quoted( cppstr_v ) << '\n';

char array[3] = {'B', 'a', 'r'};
std::string_view array_v(array, std::size(array)); // overload (3)
std::cout << "2) array_v: " << quoted( array_v ) << '\n';

const char* one_0_two = "One\0Two";

std::string_view one_two_v {one_0_two, 7}; // overload (3)
std::cout << "3) one_two_v: \"";
for (char c: one_two_v) { std::cout << (c != '\0' ? c : '?'); }
std::cout << "\", one_two_v.size(): " << one_two_v.size() << '\n';

std::string_view one_v {one_0_two}; // overload (4)
std::cout << "4) one_v: " << quoted( one_v ) << ", one_v.size(): "
<< one_v.size() << '\n';

constexpr std::wstring_view wcstr_v = L"xyzzy"; // overload (4)
std::cout << "5) wcstr_v.size(): " << wcstr_v.size() << '\n';

std::array ar = {'P', 'u', 'b'};
std::string_view ar_v(ar.begin(), ar.end()); // overload (5), C++20
std::cout << "6) ar_v: " << quoted( ar_v ) << '\n';

// std::string_view ar_v2{ar}; // overload (6), OK in C++23
// std::cout << "ar_v2: " << quoted( ar_v2 ) << '\n'; // ar_v2: "Pub"

[[maybe_unused]] auto zero = [] { /* ... */ return nullptr; };
// std::string_view s{ zero() }; // overload (7), won't compile since C++23
}

Output:¶

1) cppstr_v: "Foo"
2) array_v: "Bar"
3) one_two_v: "One?Two", one_two_v.size(): 7
4) one_v: "One", one_v.size(): 3
5) wcstr_v.size(): 5
6) ar_v: "Pub"

See also¶

operator= assigns a view
(C++17) (public member function)
constructor constructs a basic_string
(public member function of std::basic_string<CharT,Traits,Allocator>)