Log In    |    Knowledge Base    |    4D Home
Tech Tip: Pointer Notation Syntax: 4D vs. C
Published On: May 7, 2008

Pointer notation in 4D looks a bit different from the C style notation used in languages like C++. It can be tempting to assume the wrong function of a certain symbol, such as the arrow, based on familiarity with C++ in particular.

A side-by-side comparison with C++ may help to see the distinction. This assumes that objX is a C++ object of class type ObjectX.

4D Syntax C++, Simple Variable C++, Object Member
Referenced Variable myInt:=12 myInt=12; objX.myInt=12;
Declare Pointer (Not required) int *iPtr; ObjectX *oPtr;
Assign Reference myPtr:=->myInt iPtr=&myInt; oPtr=&objX;
Simple Dereference ALERT(myPtr->) cout << *iPtr; cout << oPtr->myInt;
Dereferenced Assignment myPtr->:=13 *iPtr = 13; oPtr->myInt = 13;

The arrow -> (dash plus wedge) symbol is your basic pointer dereferencing symbol in 4D, similar (but not identical) to the asterisk * in C and C++. In C++ the arrow is used as a contraction of pointer dereferencing and object member access: oPtr->myInt is equivalent to *(oPtr).myInt .

One subtle difference to note in 4D is assignment of the reference to the pointer, vs. assignment of a value to the variable deferenced by the pointer:

:=-> Assign pointer to point to the variable
->:= Assign a value to the dereferenced variable