std::basic_string_view<CharT,Traits>::basic_string_view
From cppreference.com
< cpp | string | basic string view
C++
Feature test macros (C++20)
Concepts library (C++20)
Metaprogramming library (C++11)
Ranges library (C++20)
Filesystem library (C++17)
Concurrency support library (C++11)
Execution control library (C++26)
std::basic_string_view
basic_string_view::basic_string_view
(C++20)
(C++20)
(C++23)
Constants
(until C++20)(until C++20)(until C++20)(until C++20)(until C++20)(C++20)
Deduction guides (C++20)
constexpr basic_string_view() noexcept;
(1)
(since C++17)
constexpr basic_string_view( const basic_string_view& other ) noexcept = default;
(2)
(since C++17)
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 >
constexpr basic_string_view( It first, End last );
(5)
(since C++20)
constexpr basic_string_view( It first, End last );
template< class R >
constexpr explicit basic_string_view( R&& r );
(6)
(since C++23)
constexpr explicit basic_string_view( R&& r );
basic_string_view( std::nullptr_t ) = delete;
(7)
(since C++23)
1) Default constructor. Constructs an empty
std::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
std::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 all following conditions are satisfied:
-
Itsatisfiescontiguous_iterator, -
Endsatisfiessized_sentinel_forforIt, - std::iter_value_t <It> and
CharTare the same type, and -
Endis not convertible to std::size_t .
-
6) Constructs a
std::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 all following conditions are satisfied:
- std::remove_cvref_t <R> is not the same type as
std::basic_string_view, -
Rmodelscontiguous_rangeandsized_range, - ranges::range_value_t <R> and
CharTare the same type, -
Ris not convertible to const CharT*, and - 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.
- std::remove_cvref_t <R> is not the same type as
7)
std::basic_string_view cannot be constructed from nullptr.Contents
[edit] 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
[edit] Complexity
1-3,5,6) Constant.
4) Linear in length of s.
[edit] 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: " << std::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: " << std::quoted (array_v) << '\n'; const char* one_0_two = "One0円Two"; 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円' ? 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: " << std::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: " << std::quoted (ar_v) << '\n'; // std::string_view ar_v2{ar}; // overload (6), OK in C++23 // std::cout << "ar_v2: " << std::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"
[edit] See also
constructs a
(public member function of
basic_string (public member function of
std::basic_string<CharT,Traits,Allocator>) [edit]