std::string_view find_first_of() method

since C++17

// (1) Const version only
constexpr size_type find_first_of( const basic_string& str, size_type pos = 0 ) const noexcept;

// (2) Const version only
constexpr size_type find_first_of( const CharT* s, size_type pos, size_type count ) const;

// (3) Const version only
constexpr size_type find_first_of( const CharT* s, size_type pos = 0 ) const;

// (4) Const version only
constexpr size_type find_first_of( CharT ch, size_type pos = 0 ) const noexcept;

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(c), 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
• c - character to search for

Return value

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

Complexity

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

important

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Exceptions

(none)

Example

#include <string_view>
#include <iostream>
 
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.