Boost C++ Libraries

...one of the most highly regarded and expertly designed C++ library projects in the world. — Herb Sutter and Andrei Alexandrescu, C++ Coding Standards

Find the first occurrence of any of the characters not within the string.

std::size_t
find_first_not_of(
    string_view sv,
    std::size_t pos = 0) const noexcept;
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Find the first occurrence of a character not equal to ch.

std::size_t
find_first_not_of(
    char ch,
    std::size_t pos = 0) const noexcept;
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