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

#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 << "не найдено\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', '\0'};
    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)); // не найдено
}