std::basic_..._last_not_of(3)

🌸 NAME 🌸

okay so bestie, welcome to the manual page for std::basic_..._last_not_of(3), straight out of the C++ Standard Library. The actual star is std::basic_string::find_last_not_of — yes, that whole mouthful — and it's giving “find the last character that is not in this set” energy. 💅

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✨ Synopsis ✨

size_type find_last_not_of( const basic_string& str,
                            size_type pos = npos ) const;

size_type find_last_not_of( const CharT* s,
                            size_type pos, size_type count ) const;

size_type find_last_not_of( const CharT* s,
                            size_type pos = npos ) const;

size_type find_last_not_of( CharT ch,
                            size_type pos = npos ) const;

template< class StringViewLike >
size_type find_last_not_of( const StringViewLike& t,
                            size_type pos = npos ) const
    noexcept(/* see below */);

Overload tea, in order ☕:

• overload (1) — noexcept since C++11, constexpr since C++20.
• overload (2) — constexpr since C++20.
• overload (3) — constexpr since C++20.
• overload (4) — noexcept since C++11, constexpr since C++20.
• overload (5) — since C++17, constexpr since C++20.

So what does it actually do? It finds the last character equal to none of the characters in the given character sequence. The search only looks at the range [0, pos]. And if every character in that range can be found in the given character sequence, it returns npos. No cap. 🫶

Here's the overload-by-overload breakdown:

1. Finds the last character equal to none of the characters in str.
2. Finds the last character equal to none of the characters in the range [s, s + count). This range can include null characters. 🚨 If [s, s + count) is not a valid range, the behavior is undefined — not cute, don't do it.
3. Finds the last character equal to none of the characters in the character string pointed to by s. The length of the string is determined by the first null character using Traits::length(s). 🚨 If [s, s + Traits::length(s)) is not a valid range, the behavior is undefined.
4. Finds the last character not equal to ch.
5. Implicitly converts t to a string view sv as if by std::basic_string_view<CharT, Traits> sv = t;, then finds the last character equal to none of the characters in sv. This overload participates in overload resolution only if std::is_convertible_v<const StringViewLike&, std::basic_string_view<CharT, Traits>> is true and std::is_convertible_v<const StringViewLike&, const CharT*> is false.

In all cases, equality is checked by calling Traits::eq. periodt. ✨

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🎀 Parameters 🎀

• str — string identifying characters to search for
• pos — position at which to end search
• count — length of character string identifying characters to search for
• s — pointer to a character string identifying characters to search for
• ch — character identifying characters to search for
• t — object (convertible to std::basic_string_view) identifying characters to search for

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🌈 Return value 🌈

Position of the found character, or npos if no such character is found. That's it, that's the whole vibe. 💖

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💜 Exceptions 💜

Overloads 1 and 4 throw nothing. Iconic behavior, honestly.

Overload 5 has this noexcept specification:

noexcept(std::is_nothrow_convertible_v<
    const T&, std::basic_string_view<CharT, Traits>>)

If an exception is thrown for any reason, this function has no effect — it has the strong exception safety guarantee. 🛡️

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🦋 Example 🦋

// Run this code

#include <iostream>
#include <string>

void show_pos(const std::string& str, std::string::size_type found)
{
    if (found != std::string::npos)
        std::cout << '[' << found << "] = \'" << str[found] << "\'\n";
    else
        std::cout << "not found\n";
}

int main()
{
    std::string str{"abc_123"};
    char const* skip_set{"0123456789"};
    std::string::size_type str_last_pos{std::string::npos};

    show_pos(str, str.find_last_not_of(skip_set)); // [3] = '_'

    str_last_pos = 2;
    show_pos(str, str.find_last_not_of(skip_set, str_last_pos)); // [2] = 'c'

    str_last_pos = 2;
    show_pos(str, str.find_last_not_of('c', str_last_pos)); // [1] = 'b'

    const char arr[]{'3', '4', '5'};
    show_pos(str, str.find_last_not_of(arr)); // [5] = '2'

    str_last_pos = 2;
    std::string::size_type skip_set_size{4};
    show_pos(str, str.find_last_not_of(skip_set,
                                       str_last_pos,
                                       skip_set_size)); // [2] = 'c'

    show_pos(str, str.find_last_not_of("abc")); // [6] = '3'

    str_last_pos = 2;
    show_pos(str, str.find_last_not_of("abc", str_last_pos)); // not found
}

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🌟 Output 🌟

[3] = '_'
[2] = 'c'
[1] = 'b'
[5] = '2'
[2] = 'c'
[6] = '3'
not found

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🧚 Defect reports 🧚

The following behavior-changing defect reports were applied retroactively to previously published C++ standards. History really said “let me fix that for you.” 💅

• LWG 141 — applied to C++98. Before: overload (1) could only return npos if pos >= size(). After: the search range is [0, size()) in this case.
• LWG 847 — applied to C++98. Before: there was no exception safety guarantee. After: added strong exception safety guarantee.
• LWG 2064 — applied to C++11. Before: overloads (3,4) were noexcept. After: removed.
• LWG 2946 — applied to C++17. Before: overload (5) caused ambiguity in some cases. After: avoided by making it a template.
• P1148R0 — applied to C++11, C++17. Before: noexcept for overloads (4,5) were accidentally dropped by LWG2064/LWG2946. After: restored.

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🔥 See also 🔥

• find — finds the first occurrence of the given substring (public member function)
• rfind — find the last occurrence of a substring (public member function)
• find_first_of — find first occurrence of characters (public member function)
• find_first_not_of — find first absence of characters (public member function)
• find_last_of — find last occurrence of characters (public member function)
• find_last_not_of — find last absence of characters (public member function)
• find_last_not_of — find last absence of characters (public member function of std::basic_string_view<CharT,Traits>)

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👑 Category 👑

• conditionally noexcept

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🫶 that's the whole page, bestie. source: http://cppreference.com, version/date: 2024.06.10, page: std::basic_..._last_not_of(3). mwah 💋