std::basic_..._string_view(3)

✨ std::basic_..._string_view(3) ✨

okay so this is the constructor page for std::basic_string_view, straight from the C++ Standard Libary (yes bestie, that spelling is exactly what the manual says 😭). it's giving “seven overloads walk into a group chat,” and every single one is iconic in its own way. let's get into it 💅

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🌸 NAME 🌸

std::basic_string_view::basic_string_view — std::basic_string_view::basic_string_view

yes, the name is literally the same thing twice. main character energy, fr fr.

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🎀 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 > constexpr explicit basic_string_view( R&& r );
(6) (since C++23)
constexpr basic_string_view( std::nullptr_t ) = delete;
(7) (since C++23)

the little numbers in parentheses are overload IDs, iykyk. now here's the lowdown on each one:

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.

bestie, those “undefined behavior” bits are not a vibe check you wanna fail — do not test them 🙈

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🌈 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

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⭐ Complexity ⭐

• 1-3,5,6) — Constant.
• 4) — Linear in length of s.

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🦋 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"

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👑 See also 👑

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

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that's the whole vibe, bestie — source/version http://cppreference.com, date 2024.06.10, and yes the manual name is still std::basic_..._string_view(3). go build something iconic 💖✨🫶