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

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.

# Declarations

size_type rfind( const basic_string& str, size_type pos = npos ) const;

(noexcept since C++11) (constexpr since C++20)

size_type rfind( const CharT* s, size_type pos, size_type count ) const;

(constexpr since C++20)

size_type rfind( const CharT* s, size_type pos = npos ) const;

(constexpr since C++20)

size_type rfind( CharT ch, size_type pos = npos ) const;

(noexcept since C++11) (constexpr since C++20)

template< class StringViewLike >
size_type rfind( const StringViewLike& t,
size_type pos = npos ) const noexcept(/* see below */);

(since C++17) (constexpr since C++20)

# 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.

# Example

#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);
}

# Defect reports

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 cases	avoided by making it a template
P1148R0	C++11C++17	noexcept for overloads (4,5) wereaccidently dropped by LWG2064/LWG2946	restored