std::basic_string_view<CharT,Traits>::basic_string_view
From cppreference.com
< cpp | string | basic string view
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) |
template< class R > constexpr explicit basic_string_view( R&& r ); |
(6) | (since C++23) |
constexpr 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:
-
It
satisfiescontiguous_iterator
, -
End
satisfiessized_sentinel_for
forIt
, - std::iter_value_t<It> and
CharT
are the same type, and -
End
is 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
, -
R
modelscontiguous_range
andsized_range
, - ranges::range_value_t<R> and
CharT
are the same type, -
R
is 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 = "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: " << 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
assigns a view (public member function) | |
constructs a basic_string (public member function of std::basic_string<CharT,Traits,Allocator> )
|