std::basic_string::rfind(3)

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

Synopsis
   size_type rfind( const basic_string& (until
   str, size_type pos = npos ) const; C++11)
   size_type rfind( const basic_string& (since
   str, C++11)
   size_type pos = npos ) const (until
   noexcept; C++20)
   constexpr size_type rfind( const
   basic_string& str, (since
   size_type pos = npos ) const C++20)
   noexcept;
   size_type rfind( const CharT* s, (until
   size_type pos, size_type count ) C++20)
   const;
   constexpr size_type rfind( const
   CharT* s, (since
   size_type pos, size_type count ) C++20)
   const;
   size_type rfind( const CharT* s, (until
   size_type pos = npos ) const; C++20)
   constexpr size_type rfind( const (since
   CharT* s, size_type pos = npos ) C++20)
   const;
   size_type rfind( CharT ch, size_type (1) (until
   pos = npos ) const; C++11)
                        (since
   size_type rfind( CharT ch, size_type C++11)
   pos = npos ) const noexcept; (until
                        (2) C++20)
   constexpr size_type rfind( CharT ch, (since
   size_type pos = npos ) const C++20)
   noexcept; (3)
   template < class StringViewLike >
                        (since
   size_type (4) C++17)
                        (until
   rfind( const StringViewLike& t, C++20)
   size_type pos = npos ) const
   noexcept(/* see below */); (5)
   template < class StringViewLike >
   constexpr size_type (since
                        C++20)
   rfind( const StringViewLike& t,
   size_type pos = npos ) const
   noexcept(/* see below */);
   Finds the last substring equal to the given character sequence. Search begins at
   pos, i.e. the found substring must not begin in a position following pos. If npos or
   any value not smaller than size()-1 is passed as pos, 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.
   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).
   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 (str.size(), count, or Traits::length(s) is zero)
   returns pos (the empty string is found immediately) unless pos > size() (including
   the case where pos == npos), in which case returns size().
   Otherwise, if size() is zero, npos is always returned.

Exceptions
   5)
   noexcept specification:
   noexcept(std::is_nothrow_convertible_v<const T&, std::basic_string_view<CharT,
   Traits>>)

Example
// Run this code
 #include <string>
 #include <iostream>
 void print(std::string::size_type n, std::string const &s)
 {
     if (n == std::string::npos) {
         std::cout << "not found\n";
     } else {
         std::cout << "found: \"" << s.substr(n) << "\" 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, s);
     // search backwards from position 4
     n = s.rfind("is", 4);
     print(n, s);
     // find a single character
     n = s.rfind('s');
     print(n, s);
     // find a single character
     n = s.rfind('q');
     print(n, s);
 }

Output:
 found: "is a string" at 5
 found: "is is a string" at 2
 found: "string" at 10
 not found
  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 2064 C++11 overload (3) and (4) were noexcept removed
   LWG 2946 C++17 string_view overload causes ambiguity in avoided by making it a
                       some cases template
   P1148R0 C++11 noexcept for overload (4)/(5) was restored
            C++17 accidently dropped by LWG2064/LWG2946

See also
   find find characters in the string
                     (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)
   rfind find the last occurrence of a substring
   (C++17) (public member function of std::basic_string_view<CharT,Traits>)