Method append_for_single_quote

sql/sql_string.cc:1146–1168

*/
#define APPEND(...)   if (append(__VA_ARGS__)) return 1;
bool String::append_for_single_quote(const char *st, size_t len)
{
  const char *end= st+len;
  int chlen;
  for (; st < end; st++)
  {
    char ch2= (char) (uchar) escaped_wc_for_single_quote((uchar) *st);
    if (ch2)
    {
      if (append('\\') || append(ch2))
        return true;
      continue;
    }
    if ((chlen= charset()->charlen(st, end)) > 0)
    {
     APPEND(st, chlen);
      st+= chlen-1;
    }
    else
      APPEND(*st);
  }
  return 0;
}


bool String::append_for_single_quote_using_mb_wc(const char *src,