How to access FlexLexer's input function without deriving from yyFlexLexer?

Question

I am writing a simple compiler for a simple C like language. To do that I would like to use Flex and Bison but use them both in the context of modern C++ Right now my setup consists of a main.cpp which just instantiates the scanner and parser and starts parsing

// some includes here

#include <FlexLexer.h>
#include "parser.tab.hh"

FlexLexer* scanner;

int main(int argc, char **argv) {
    yy::parser p;
    scanner = new yyFlexLexer;
    // boilerplate
    if (!p()) std::cout << "No errors detected\n";
}

scanner.l

%option c++ noyywrap

D           [0-9]
L           [a-zA-Z_]
H           [a-fA-F0-9]
E           [Ee][+-]?{D}+
FS          (f|F|l|L)
IS          (u|U|l|L)*

%{
// Several includes

#include "parser.tab.hh"

using token = yy::parser::token;

void count();
void comment();
int check_type();
void add_symbol(void);

void yyerror(const char *);
extern std::map<std::string, std::vector<int>> symbol_table;
extern FlexLexer* scanner;
%}
%%
"/*"            { comment(); }

// skipped for brevity

%%
void comment(void)
{
    int c;
    while ((c = scanner->input()) != 0)
        if (c == '*')
        {
            while ((c = scanner->input()) == '*');

            if (c == '/')
                return;

            if (c == 0)
                break;
        }
    yyerror("unterminated comment");
}

and finally parser.yy which looks like the Ansi C yacc grammar with the addition of this at the top

%require "3.2"
%language "c++"
%skeleton "lalr1.cc"

%{
extern int yylex();
%}

%define api.token.constructor
%define api.value.type variant
%define parse.assert

...

This setup does not compile of course as FlexLexer does not have a member called input(), however instantiating yyFlexLexer is also not an option as the input() function of that class is protected and not usable. The Flex manual states one must use yyinput() when generating C++ code in flex and uses it as a free standing function which is not available for some reason on my setup. https://ftp.gnu.org/old-gnu/Manuals/flex-2.5.4/html_node/flex_19.html

My question is thus: Is it possible, and if so how, to access the default input() functionality when also using the C++ option of Flex, without resorting to creating a separate Lexer class that derives from yyFlexLexer?