std::basic_string_view<CharT,Traits>::find_first_of

From cppreference.com
 
 
 
 
constexpr size_type find_first_of( basic_string_view v, size_type pos = 0 ) const noexcept;
(1) (since C++17)
constexpr size_type find_first_of( CharT ch, size_type pos = 0 ) const noexcept;
(2) (since C++17)
constexpr size_type find_first_of( const CharT* s, size_type pos, size_type count ) const;
(3) (since C++17)
constexpr size_type find_first_of( const CharT* s, size_type pos = 0 ) const;
(4) (since C++17)

Finds the first character equal to any of the characters in the given character sequence.

1) Finds the first occurrence of any of the characters of v in this view, starting at position pos.
2) Equivalent to find_first_of(basic_string_view(std::addressof(ch), 1), pos).
3) Equivalent to find_first_of(basic_string_view(s, count), pos).
4) Equivalent to find_first_of(basic_string_view(s), pos).

Parameters

v - view to search for
pos - position at which to start the search
count - length of the string of characters to search for
s - pointer to a string of characters to search for
ch - character to search for

Return value

Position of the first occurrence of any character of the substring, or npos if no such character is found.

Complexity

O(size() * v.size()) at worst.

Example

#include <iostream>
#include <string_view>
 
int main()
{
    using namespace std::literals;
    constexpr auto N = std::string_view::npos;
 
    auto is_white_space = [](const char c) noexcept
    {
        return " \t\n\f\r\v"sv.find_first_of(c) != N;
    };
 
    static_assert(
        1 == "alignas"sv.find_first_of("klmn"sv) &&
          //   └─────────────────────────┘
        N == "alignof"sv.find_first_of("wxyz"sv) &&
          //
        3 == "concept"sv.find_first_of("bcde"sv, /* pos= */ 1) &&
          //     └───────────────────────┘
        N == "consteval"sv.find_first_of("oxyz"sv, /* pos= */ 2) &&
          //
        6 == "constexpr"sv.find_first_of('x') &&
          //        └─────────────────────┘
        N == "constinit"sv.find_first_of('x') &&
          //
        6 == "const_cast"sv.find_first_of('c', /* pos= */ 4) &&
          //        └──────────────────────┘
        N == "continue"sv.find_first_of('c', /* pos= */ 42) &&
          //
        5 == "co_await"sv.find_first_of("cba", /* pos= */ 4) &&
          //       └───────────────────────┘
        7 == "decltype"sv.find_first_of("def", /* pos= */ 2, /* count= */ 2) &&
          //         └────────────────────┘
        N == "decltype"sv.find_first_of("def", /* pos= */ 2, /* count= */ 1) &&
          //
        is_white_space(' ') && is_white_space('\r') && !is_white_space('\a')
    );
    std::cout << "All tests passed.\n";
}

Output:

All tests passed.

See also

(C++17)
find characters in the view
(public member function)
(C++17)
find the last occurrence of a substring
(public member function)
find last occurrence of characters
(public member function)
find first absence of characters
(public member function)
find last absence of characters
(public member function)
find first occurrence of characters
(public member function of std::basic_string<CharT,Traits,Allocator>)