std::basic_string<CharT,Traits,Allocator>::rfind

 

C++

Compiler support

Freestanding and hosted

Language

Standard library headers

Named requirements

Feature test macros (C++20)

Language support library

Concepts library (C++20)

Diagnostics library

General utilities library

Strings library

Containers library

Iterators library

Ranges library (C++20)

Algorithms library

Numerics library

Localizations library

Input/output library

Filesystem library (C++17)

Regular expressions library (C++11)

Atomic operations library (C++11)

Thread support library (C++11)

Technical specifications

Symbols index

External libraries

 

Strings library

Null-terminated strings

Byte strings

Multibyte strings

Wide strings

Classes

basic_string

basic_string_view (C++17)

char_traits

 

std::basic_string

Member functions basic_string::basic_string basic_string::operator= basic_string::assign basic_string::get_allocator Element access basic_string::at basic_string::operator[] basic_string::front (C++11) basic_string::back (C++11) basic_string::data basic_string::c_str basic_string::operator  basic_string_view (C++17) Iterators basic_string::beginbasic_string::cbegin (C++11) basic_string::endbasic_string::cend (C++11) basic_string::rbeginbasic_string::crbegin (C++11) basic_string::rendbasic_string::crend (C++11) Capacity basic_string::empty basic_string::sizebasic_string::length basic_string::max_size basic_string::reserve basic_string::capacity basic_string::shrink_to_fit (C++11)   Operations basic_string::clear basic_string::insert basic_string::erase basic_string::push_back basic_string::pop_back (C++11) basic_string::append basic_string::operator+= basic_string::compare basic_string::starts_with (C++20)   basic_string::ends_with (C++20) basic_string::contains (C++23) basic_string::replace basic_string::substr basic_string::copy basic_string::resize basic_string::resize_and_overwrite (C++23) basic_string::swap

Search basic_string::find basic_string::rfind basic_string::find_first_of basic_string::find_first_not_of basic_string::find_last_of basic_string::find_last_not_of Constants basic_string::npos Deduction guides (C++17) Non-member functions operator+ swap(std::basic_string) operator""s (C++14) erase(std::basic_string)erase_if(std::basic_string) (C++20)(C++20) I/O operator<<operator>> getline Comparison operator==operator!=operator<operator>operator<=operator>=operator<=> (until C++20)(until C++20)(until C++20)(until C++20)(until C++20)(C++20) Numeric conversion stoistolstoll (C++11)(C++11)(C++11) stoulstoull (C++11)(C++11) stofstodstold (C++11)(C++11)(C++11) to_string (C++11) to_wstring (C++11) Helper classes hash<std::string>hash<std::wstring>hash<std::u32string>hash<std::u16string>hash<std::u8string> (C++11)  (C++11)(C++11)(C++11)(C++20) hash<std::pmr::string>hash<std::pmr::wstring>hash<std::pmr::u32string>hash<std::pmr::u16string>hash<std::pmr::u8string> (C++17)(C++17)(C++17)(C++17)(C++20)

 

	(1)
size_type rfind( const basic_string& str, size_type pos = npos ) const;			(until C++11)
size_type rfind( const basic_string& str,                  size_type pos = npos ) const noexcept;			(since C++11) (until C++20)
constexpr size_type rfind( const basic_string& str,                            size_type pos = npos ) const noexcept;			(since C++20)
		(2)
size_type rfind( const CharT* s, size_type pos, size_type count ) const;				(until C++20)
constexpr size_type rfind( const CharT* s,                            size_type pos, size_type count ) const;				(since C++20)
			(3)
size_type rfind( const CharT* s, size_type pos = npos ) const;					(until C++20)
constexpr size_type rfind( const CharT* s, size_type pos = npos ) const;					(since C++20)
				(4)
size_type rfind( CharT ch, size_type pos = npos ) const;						(until C++11)
size_type rfind( CharT ch, size_type pos = npos ) const noexcept;						(since C++11) (until C++20)
constexpr size_type rfind( CharT ch, size_type pos = npos ) const noexcept;						(since C++20)
					(5)
template < class T > size_type     rfind( const T& t, size_type pos = npos ) const noexcept(/* see below */);							(since C++17) (until C++20)
template < class T > constexpr size_type     rfind( const T& t, size_type pos = npos ) const noexcept(/* see below */);							(since C++20)

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 T&, std::basic_string_view<CharT, Traits>> is true and std::is_convertible_v<const T&, 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 some cases	avoided by making it a template
P1148R0	C++11 C++17	noexcept for overload (4)/(5) was accidently dropped by LWG2064/LWG2946	restored

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 (C++17)	find the last occurrence of a substring (public member function of std::basic_string_view<CharT,Traits>)