std::ctype:...type::do_is(3)

🎀 NAME 🎀

okay bestie, this is std::ctype::is and std::ctype::do_is — and yes, the NAME is literally std::ctype::is,std::ctype::do_is - std::ctype::is,std::ctype::do_is, twice, because the manpage said it and we're keeping the receipts 💅. It comes from the C++ Standard Libary manual, page id std::ctype:...type::do_is(3). We're so back.

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✨ Synopsis ✨

Defined in header <locale> 💖

public:
(1)
bool is( mask m, CharT c ) const;
public:
(2)
const CharT* is( const CharT* low, const CharT* high, mask* vec )
const;
protected:
(3)
virtual bool do_is( mask m, CharT c ) const;
protected:
virtual const CharT* do_is( const CharT* low, const CharT* high,
mask* vec )    (4)
const;

okay so what's the tea:

• 1,2) — Public member function, calls the protected virtual member function do_is of the most derived class.
• 3) — Checks if the character c is classified by the mask m.
• 4) — For every character in the character array [low, high), identifies the complete classification mask (e.g. digit|xdigit|alnum|print|graph for the digit '0' in the default locale), and stores the masks in the corresponding elements of the array pointed to by vec.

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🌸 Parameters 🌸

• c — character to classify
• m — mask to use for classifying a single character
• low — pointer to the first character in an array of characters to classify
• high — one past the end pointer for the array of characters to classify
• vec — pointer to the first element of the array of masks to fill

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💖 Return value 💖

• 1,3) — true if c is classified by m.
• 2,4) — high

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🧚 Example 🧚

Run this code, bestie — exact example, no cap:

        #include <cstddef>
        #include <iostream>
        #include <locale>
        #include <utility>
        #include <vector>

        // utility wrapper to make locale-bound facets destructible
        template<class Facet>
        struct deletable_facet : Facet
        {
            template<class ...Args>
            deletable_facet(Args&& ...args) :
       Facet(std::forward<Args>(args)...) {}
            ~deletable_facet() {}
        };

        int main()
        {
            // classify a single character using the default locale
            auto& f = std::use_facet<std::ctype<char>>(std::locale());
            char c = '0';
            if (f.is(std::ctype_base::digit, c)) // or isdigit(c, locale());
                std::cout << '\'' << c << "' is a digit\n";

            // classify every character in a string using a named locale
            deletable_facet<std::ctype_byname<wchar_t>> f2("en_US.utf8");
            std::wstring str = L"z\u00df\u6c34\U0001d10b";
            std::vector<std::ctype_base::mask> vec(str.size());
            f2.is(&str[0], &str[0] + str.size(), &vec[0]);

            for (std::size_t n = 0; n < str.size(); ++n)
            {
                std::cout << std::hex << "U+" << static_cast<wint_t>(str[n]) <<
       " is: ";
                if (vec[n] & std::ctype_base::alnum)
                    std::cout << "alnum";
                if (vec[n] & std::ctype_base::punct)
                    std::cout << "punct";
                std::cout << '\n';
            }
        }

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🌈 Output 🌈

'0' is a digit
U+7a is: alnum
U+df is: alnum
U+6c34 is: alnum
U+1d10b is: punct

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🦋 See also 🦋

• is — classifies a character or a character sequence, using the classification table (public member function of std::ctype<char>)
• iswctype — classifies a wide character according to the specified LC_CTYPE category (function)

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source: http://cppreference.com · version/page: std::ctype:...type::do_is(3) · date: 2024.06.10 💜