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

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< cpp‎ | string‎ | basic string view

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

Run this code

    #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

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

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