function pointers in c++ : error: must use '.*' or '->*' to call pointer-to-member function in function

Question

Code snippet is as follows. Not able to understand why I am getting this error.

void
SipObj::check_each_field()
{
  map <std::string, sip_field_getter>::iterator msg;
  string str;
  char name[20];
  bool res = false;
  sscanf(get_payload(), "%s %*s", name);
  LOGINFO(lc()) <<  "INVITE:" << name;
  str = name;
  msg = sip_field_map.find(str);
  if (msg != sip_field_map.end()) {
      sip_field_getter sip_field = msg->second;
      res = (this).*sip_field();
  }
}

 typedef bool (SipObj::*sip_field_getter)();
 static map <std::string, sip_field_getter> sip_field_map;

sip_field_getter is a place holder for function names

Answer 1

(this).*sip_field();

There are two problems with this expression:

1. this is a pointer, so you must use ->* to call a member function via pointer on it.

2. the function call (()) has higher precedence than the member-by-pointer operators (either .* or ->*), so you need parentheses to correctly group the expression.

The correct expression is:

(this->*sip_field)();