4.6. The Member Access Operators

The dot (§ 1.5.2, p. 23) and arrow (§ 3.4.1, p. 110) operators provide for member access. The dot operator fetches a member from an object of class type; arrow is defined so that ptr->mem is a synonym for (*ptr).mem:

string s1 = "a string", *p = &s1;
auto n = s1.size(); // run the size member of the string s1
n = (*p).size();    // run size on the object to which p points
n = p->size();      // equivalent to (*p).size()

Because dereference has a lower precedence than dot, we must parenthesize the dereference subexpression. If we omit the parentheses, this code means something quite different:

// run the size member of p, then dereference the result!
*p.size();    // error: p is a pointer and has no member named size

This expression attempts to fetch the size member of the object p. However, p is a pointer, which has no members; this code will not compile.

The arrow operator requires a pointer operand and yields an lvalue. The dot operator yields an lvalue if the object from which the member is fetched is an lvalue; otherwise the result is an rvalue.

INFO

Exercises Section 4.6

Exercise 4.20: Assuming that iter is a vector<string>::iterator, indicate which, if any, of the following expressions are legal. Explain the behavior of the legal expressions and why those that aren’t legal are in error.

(a)*iter++;

(b)(*iter)++;

(c)*iter.empty()

(d)iter->empty();

(e)++*iter;

(f)iter++->empty();