std::basic_...irst_not_of(3)

✨ NAME ✨

std::basic_string::find_first_not_of — the member function of std::basic_string that finds the first character equal to none of the characters in a given character sequence. Bestie, this is the one from the C++ Standard Library and she is lowkey iconic for pattern-matching.

---

🌸 SYNOPSIS 🌸

size_type find_first_not_of( const basic_string& str,    (1)
(noexcept since C++11)
                               size_type pos = 0 ) const;
(constexpr since C++20)
size_type find_first_not_of( const CharT* s,
                             size_type pos, size_type    (2)
(constexpr since C++20)
count ) const;
size_type find_first_not_of( const CharT* s,             (3)
(constexpr since C++20)
                               size_type pos = 0 ) const;
size_type find_first_not_of( CharT ch, size_type pos = 0 (4)
(noexcept since C++11)
) const;
(constexpr since C++20)
template< class StringViewLike >

size_type                                                    (since
C++17)
    find_first_not_of( const StringViewLike& t,          (5)
(constexpr since C++20)

                       size_type pos = 0 ) const
noexcept(/* see below */);

Finds the first character equal to none of the characters in the given character sequence. The search considers only the range [pos, size()). If all characters in the range can be found in the given character sequence, npos will be returned.

1. Finds the first character equal to none of characters in str.
2. Finds the first character equal to none of characters in range [s, s + count). This range can include null characters. If [s, s + count) is not a valid range, the behavior is undefined.
3. Finds the first character equal to none of characters in 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 first 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 first character equal to none of 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.

---

🎀 PARAMETERS 🎀

• str — string identifying characters to search for
• pos — position for the search to start from
• 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

---

💖 RETURN VALUE 💖

Position of the found character, or std::string::npos if no such character is found. Periodt.

---

🦋 EXCEPTIONS 🦋

1,4) Throws nothing. Literally nothing. The calmest overloads in the game.

5. 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 (strong exception safety guarantee). So even if things go off the rails, your string stays unbothered. 💅

---

⭐ EXAMPLE ⭐

// Run this code

#include <iostream>
#include <string>

int main()
{
    // Permit uppercase letters, lowercase letters and numbers in macro names
    const char* pattern = "ABCDEFGHIJKLMNOPQRSTUVWXYZ"
                          "abcdefghijklmnopqrstuvwxyz"
                          "0123456789";

    std::string data = "1) %FIX, 2) %HACK, and 3) %TODO";
    const std::string replacement = "%DONE%";

    std::cout << "Before: " << data << '\n';

    for (std::string::size_type first{}, last{};
        (first = data.find('%', first)) != std::string::npos;
        first += replacement.size())
    {
        last = data.find_first_not_of(pattern, first + 1);
        if (last == std::string::npos)
            last = data.length();

        // Now first at '%' and last is one past end of the found substring
        data.replace(first, last - first, replacement);
    }

    std::cout << "After: " << data << '\n';
}

Output:

Before: 1) %FIX, 2) %HACK, and 3) %TODO
After: 1) %DONE%, 2) %DONE%, and 3) %DONE%

---

🌈 DEFECT REPORTS 🌈

The following behavior-changing defect reports were applied retroactively to previously published C++ standards. The way the committee keeps tweaking these overloads... we love an evolving icon. 🫶

• LWG 847 — Applied to: C++98 — Behavior as published: there was no exception safety guarantee — Correct behavior: added strong exception safety guarantee
• LWG 2064 — Applied to: C++11 — Behavior as published: overloads (3,4) were noexcept — Correct behavior: removed
• LWG 2946 — Applied to: C++17 — Behavior as published: overload (5) caused ambiguity in some cases — Correct behavior: avoided by making it a template
• P1148R0 — Applied to: C++11 and C++17 — Behavior as published: noexcept for overloads (4,5) were accidentally dropped by LWG2064/LWG2946 — Correct behavior: restored

---

👑 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_last_of — find last occurrence of characters (public member function)
• find_last_not_of — find last absence of characters (public member function)
• find_first_not_of — find first absence of characters (public member function of std::basic_string_view<CharT,Traits>)

---

🍓 CATEGORY 🍓

• conditionally noexcept

---

Source: cppreference.com · Version: 2024.06.10

That's the whole vibe, bestie — go forth and find_first_not_of with confidence. 💜✨