Variable length argument list error

many years ago I wrote a custom print function declared like this:

void my_printf(char *format_string, ... )
{
    // too complex to list here
}

and I could call it like this:

my_printf("Number of apples = %d\n",apple);

This function has always worked perfectly. I now wish to make a wrapper function that takes an extra integer at the start like this:

void my_printf_extra(int extra,char *format_string, ... )

that could be called like this:

my_printf_extra(debug_level,"Number of apples = %d\n",apple);

and I would like the wrapper function to call the original in a way something like this:

void my_printf_extra(int extra,char *format_string, ... )
{
    if (extra == some_test)
    {
        my_printf(** not quite sure what goes here **);
    }
}

My guess was this:

void my_printf_extra(int extra,char *format_string, ... )
{
    va_list vptr;

    if (extra == some_test)
    {
        va_start(vptr,format_string);
        my_printf(format_string,vptr);
        va_end(vptr);
    }
}

but it's not working. In my final output I see

Number of apples = -46467968

or some such garbage number (when the true value was 1). I see similar garbage when calling my_printf_extra with a string. I suspect that my processing of va_list is wrong, but I can not fathom how exactly.

EDIT: my_printf() is super flexible and can print to all sorts of different places. Sometimes it just appends the text to a rich-edit-control-window. It all depends on assorted flags as well as the contents of what's being printed.