std::basic_string::find_first_of(3)

NAME
std::basic_string::find_first_of - std::basic_string::find_first_of

Synopsis
   size_type find_first_of( const basic_string& str, (1) (noexcept since C++11)
   size_type pos = 0 ) const; (constexpr since C++20)
   size_type find_first_of( const CharT* s,
                        size_type pos, size_type count (2) (constexpr since C++20)
   ) const;
   size_type find_first_of( const CharT* s, size_type pos = (3) (constexpr since C++20)
   0 ) const;
   size_type find_first_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_of( const StringViewLike& t, (5) (constexpr since C++20)
                      size_type pos = 0 ) const noexcept(/*
   see below */);
   Finds the first character equal to one of the characters in the given character
   sequence. The search considers only the range [pos, size()). If none of the
   characters in the given character sequence is present in the range, npos will be
   returned.
   1) Finds the first character equal to one of the characters in str.
   2) Finds the first character equal to one of the characters in the 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 one of the 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 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 one of the 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.

Parameters
   str - string identifying characters to search for
   pos - position at which to begin searching
   count - length of character string identifying characters to search for
   s - pointer to a character string identifying characters to search for
   ch - character to search for
   t - object (convertible to std::basic_string_view) identifying characters to
           search for

Return value
   Position of the found character or npos if no such character is found.

Exceptions
   1,4) Throws nothing.
   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).

Notes
   Traits::eq() is used to perform the comparison.

Example
// Run this code
 #include <cassert>
 #include <iostream>
 #include <string>
 #include <string_view>
 int main()
 {
     using namespace std::literals;
     std::string::size_type sz;
     // (1)
     sz = "alignas"s.find_first_of("klmn"s);
     // └────────────────────────┘
     assert(sz == 1);
     sz = "alignof"s.find_first_of("wxyz"s);
     // no match
     assert(sz == std::string::npos);
     // (2)
     sz = "consteval"s.find_first_of("xyzabc", 0, 3);
     // no match (× are not targets) ×××
     assert(sz == std::string::npos);
     sz = "consteval"s.find_first_of("xyzabc", 0, 6);
     // └───────────────────────────────┘
     assert(sz == 0);
     // (3)
     sz = "decltype"s.find_first_of("xyzabc");
     // └────────────────────────────┘
     assert(sz == 2);
     // (4)
     sz = "co_await"s.find_first_of('a');
     // └──────────────────────┘
     assert(sz == 3);
     // (5)
     sz = "constinit"s.find_first_of("int"sv);
     // └─────────────────────────┘
     assert(sz == 2);
     std::cout << "All tests passed.\n";
 }

Output:
 All tests passed.
   Defect reports
   The following behavior-changing defect reports were applied retroactively to
   previously published C++ standards.
      DR Applied to Behavior as published Correct behavior
   LWG 847 C++98 there was no exception safety guarantee added strong exception
                        safety guarantee
   LWG 2064 C++11 overloads (3,4) were noexcept removed
   LWG 2946 C++17 overload (5) caused ambiguity in some avoided by making it a
                       cases template
   P1148R0 C++11 noexcept for overloads (4,5) were restored
            C++17 accidentally dropped by LWG2064/LWG2946

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_not_of find first absence 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 occurrence of characters
   find_first_of (public member function of std::basic_string_view<CharT,Traits>)
                     returns the length of the maximum initial segment that consists
   strspn of only the characters found in another byte string
                     (function)

Category:
     * conditionally noexcept