std::basic_string_view<CharT,Traits>:: basic_string_view

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

• 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 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

• std:: remove_cvref_t < R > is not the same type as std::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 * , 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.

7) std::basic_string_view cannot be constructed from nullptr .

1-3,5,6) Constant.

4) Linear in length of s .

#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
}

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"