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

Finds the last character equal to none of the characters in the given character sequence. The search considers only the range [0,pos]. If all characters in the range can be found in the given character sequence, npos will be returned.

# Declarations

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

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

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

(constexpr since C++20)

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

(constexpr since C++20)

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

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

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

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

# Parameters

str: string identifying characters to search for
pos: position at which to end search
count: length of character string identifying characters to search for
s: pointer to a character string identifying characters to search for
ch: character identifying characters to search for
t: object (convertible to std::basic_string_view) identifying characters to search for

# Return value

Position of the found character or npos if no such character is found.

# Example

#include <iostream>
#include <string>
 
void show_pos(const std::string& str, std::string::size_type found)
{
    if (found != std::string::npos)
        std::cout << '[' << found << "] = \'" << str[found] << "\'\n";
    else
        std::cout << "not found\n";
}
 
int main()
{
    std::string str{"abc_123"};
    char const* skip_set{"0123456789"};
    std::string::size_type str_last_pos{std::string::npos};
 
    show_pos(str, str.find_last_not_of(skip_set)); // [3] = '_'
 
    str_last_pos = 2;
    show_pos(str, str.find_last_not_of(skip_set, str_last_pos)); // [2] = 'c'
 
    str_last_pos = 2;
    show_pos(str, str.find_last_not_of('c', str_last_pos)); // [1] = 'b'
 
    const char arr[]{'3', '4', '5'};
    show_pos(str, str.find_last_not_of(arr)); // [5] = '2'
 
    str_last_pos = 2;
    std::string::size_type skip_set_size{4};
    show_pos(str, str.find_last_not_of(skip_set,
                                       str_last_pos,
                                       skip_set_size)); // [2] = 'c'
 
    show_pos(str, str.find_last_not_of("abc")); // [6] = '3'
 
    str_last_pos = 2;
    show_pos(str, str.find_last_not_of("abc", str_last_pos)); // not found
}

# Defect reports

DR	Applied to	Behavior as published	Correct behavior
LWG 141	C++98	overload (1) could only return npos if pos >= size()	the search range is[0, size()) in this case
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) wereaccidentally dropped by LWG2064/LWG2946	restored