std::basic_string::rfind(3)

NAME
std::basic_string::rfind - std::basic_string::rfind

Synopsis
   size_type rfind( const basic_string& str, size_type pos (1) (noexcept since C++11)
   = npos ) const; (constexpr since C++20)
   size_type rfind( const CharT* s, size_type pos, (2) (constexpr since C++20)
   size_type count ) const;
   size_type rfind( const CharT* s, size_type pos = npos ) (3) (constexpr since C++20)
   const;
   size_type rfind( CharT ch, size_type pos = npos ) const; (4) (noexcept since C++11)
                        (constexpr since C++20)
   template< class StringViewLike >
   size_type rfind( const StringViewLike& t, (5) (since C++17)
                        (constexpr since C++20)
                    size_type pos = npos ) const
   noexcept(/* see below */);
   Finds the last substring that is equal to the given character sequence. The search
   begins at pos and proceeds from right to left (thus, the found substring, if any,
   cannot begin in a position following pos). If npos or any value not smaller than
   size() - 1 is passed as pos, the whole string will be searched.
   1) Finds the last substring equal to str.
   2) Finds the last substring equal to 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 last substring equal to the 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 last 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 last substring equal to the contents of 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.
   In all cases, equality is checked by calling Traits::eq.

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

Return value
   Position of the first character of the found substring or npos if no such substring
   is found. Note that this is an offset from the start of the string, not the end.
   If searching for an empty string (i.e., str.size(), count, or Traits::length(s) is
   zero), the empty string is found immediately and rfind returns:
     * pos, if pos < size();
     * size() otherwise, including the case where pos == npos.
   Otherwise, if size() is zero, npos is always returned.

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).

Example
// Run this code
 #include <iomanip>
 #include <iostream>
 #include <string>
 void print(std::string::size_type n,
            std::string::size_type len,
            std::string const &s)
 {
     if (n == std::string::npos)
         std::cout << "not found\n";
     else
         std::cout << "found: " << std::quoted(s.substr(n, len)) << " at " << n << '\n';
 }
 int main()
 {
     std::string::size_type n;
     std::string const s = "This is a string";
     // search backwards from end of string
     n = s.rfind("is");
     print(n, 2, s);
     // search backwards from position 4
     n = s.rfind("is", 4);
     print(n, 2, s);
     // find a single character
     n = s.rfind('s');
     print(n, 1, s);
     // find a single character
     n = s.rfind('q');
     print(n, 1, s);
     // find the prefix (see also s.starts_with("This"))
     n = s.rfind("This", 0);
     print(n, 4, s);
 }

Output:
 found: "is" at 5
 found: "is" at 2
 found: "s" at 10
 not found
 found: "This" at 0
   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 accidently dropped by LWG2064/LWG2946

See also
   find finds the first occurrence of the given substring
                     (public member function)
   find_first_of find first occurrence of characters
                     (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 the last occurrence of a substring
   rfind (public member function of std::basic_string_view<CharT,Traits>)

Category:
     * conditionally noexcept