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std::basic_..._string_view(3) C++ Standard Libarystd::basic_..._string_view(3) NAME std::basic_string_view::basic_string_view - std::basic_string_view::ba- sic_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 con- structor 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 ac- tually model contiguous_iterator, or if End does not actually model sized_sen- tinel_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 construc- tion, 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 ba- sic_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::ba- sic_string<CharT,Traits,Allocator>) http://cppreference.com 2022.07.31 std::basic_..._string_view(3)
NAME | Synopsis | Parameters | Complexity | Example | Output: | See also
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