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std::basic_string::rfind

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

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 (equality is checked by calling Traits::eq), as if by rfind(std::basic_string_view<CharT, Traits>(str), pos) (since C++17)

2) Finds the last substring equal to the first count characters of the character string pointed to by s. s can include null characters. Equivalent to rfind(std::basic_string(s, count), pos) (until C++17)rfind(std::basic_string_view<CharT, Traits>(s, count), pos) (since C++17)

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. Equivalent to rfind(std::basic_string(s), pos) (until C++17)rfind(std::basic_string_view<CharT, Traits>(s), pos) (since C++17)

4) Finds the last character ch. Equivalent to rfind(std::basic_string(1,c),pos)

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 only participates in overload resolution 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.

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 strlen(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

1-4) (none)	(until C++11)
1,4) `noexcept` specification: `noexcept` 2,3) (none)	(since C++11) (until C++14)
1) `noexcept` specification: `noexcept` 2,3,4) (none)	(since C++14)
5) Throws nothing unless the initialization of `sv` throws an exception.	(since C++17)

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 2946	C++17	`string_view` overload causes ambiguity in some cases	avoided by making it a template

Example

#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