std::ctype::scan_not(3)

💅 NAME 💅

std::ctype::scan_not — bestie, it's literally std::ctype::scan_not. That's the whole name, no notes. 🎀

This one lives in the C++ Standard Library and it's from the <locale> girlies ✨

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✨ Synopsis ✨

Okay so first things first, this is defined in header <locale>, k? Don't come for me if you forget the include. 🫶

const char* scan_not( mask m, const char* beg, const char* end ) const;

🌸 What it actually does 🌸

It locates the first character in the character array [beg, end) that does not satisfy the classification mask m. That is, the very first character c such that

table()[(unsigned char)c] & m

would return false. Iconic behavior honestly. 👑

Lowkey important caveat bestie: if (unsigned char)c >= std::ctype<char>::table_size, then an implementation-defined value gets substituted instead of table()[(unsigned char)c] — and it's possibly different for different values of c. So like... don't vibe too hard on that edge case, mwah. 💀

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🦋 Parameters 🦋

• m — the mask to search for 💅
• beg — pointer to the first character in an array of characters to search 🎀
• end — the one-past-the-end pointer for the array of characters to search 🌈

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⭐ Return value ⭐

A pointer to the first character in [beg, end) that does not satisfy the mask — or end if no such character was found. So if everybody in the group chat passes the vibe check, you just get end back. Periodt. 🧚

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💜 Notes 💜

Unlike the primary template std::ctype, this specialization doesn't perform a virtual function call when classifying characters. No virtual dispatch, no drama, we love to see it. ✨

To customize the behavior, a derived class may provide a non-default classification table to the base class constructor. That's your main character move right there. 🔥

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🍓 Example 🍓

// Run this code

#include <iostream>
#include <iterator>
#include <locale>

int main()
{
    auto& f = std::use_facet<std::ctype<char>>(std::locale());

    // skip leading whitespace
    char s1[] = "      \t\t\n  Test";
    const char* p1 = f.scan_not(std::ctype_base::space, std::begin(s1), std::end(s1));
    std::cout << '\'' << p1 << "'\n";

    // skip leading digits
    char s2[] = "123456789abcd";
    const char* p2 = f.scan_not(std::ctype_base::digit, std::begin(s2), std::end(s2));
    std::cout << '\'' << p2 << "'\n";
}

Output:

'Test'
'abcd'

See? We skipped the whitespace, we skipped the digits, and what's left is giving clean string. Ate. 💅💖

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🎀 See also 🎀

• do_scan_not — locates the first character in a sequence that fails given classification — [virtual] (virtual protected member function of std::ctype<CharT>) 🌸
• scan_is — locates the first character in a sequence that conforms to given classification, using the classification table (public member function) 🦋

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Okay that's the whole page bestie, ily, go read your locale facets responsibly 🫶

Source: http://cppreference.com · Version: 2024.06.10 · Page: std::ctype::scan_not(3) — drink water, unplug your charger at 80%, and ngl this doc was kinda iconic. 💜👑