C Technical Notes 1 3

( C++ Technical Notes-Number 1 H. Kanner Development Systems Group 29 February 1988 This is the first of a series of technical notes on the C++ language. Because there is as yet only one book on the language, TM C++ Programming Language by Bjarne Stroustrup, and many sections of the book have been written in a difficult to follow style, I felt that it might be of use to write some notes on various aspects of the language with which I initially had difficulty. By the way, the cited book will be refeITed to here and henceforth as The Book. It has often been said that the ultimate definition of a programming language is the official compiler. That is, the semantics of a piece of source code is really understood by inspecting the output of the compiler. In the case of the AT&T C++ compiler, this task is made easier by the fact that this output is C code. I cannot too strongly recommend to readers that they try to clear up linguistic obscurities by con- sttucting the simplest possible test cases, running them through cfront, and looking at the output. One warning: do not try this with an inliM function. This fust note deals with references. I anticipate a minimum of two more notes, to be published when I feel I understand the subjects sufticiendy. They will respectively cover constructors and destn1etors, with emphasis on their storage management aspects, and overloaded opezators, with emphasis on the dis- tinction between defining them as TMmbers or friends. I had a little difficulty understanding why references had been introduced into C++. They are an exception to the symmetry of the terrible C notation for declarations, in which one can at least say that operators such as •, Q,_311d Dhave the same meaning when used in a declaration as when used in an expres- sion. That is, char *s; char* t; char c • *t; all use the * to denote dereferencing a pointer. The first of the above three lines should literally be read: "If you were to dereferences, you would get a char." It is ttue that the compiler does not care where the white space is, and Bjame prefers the style of the second line, which he likes to state as "t is a pointer to char," as if char* represented the type "pointer to char." This is very informal. In fact he cautions that if you wril8 ._ chait"* s,t,u; only the first~ dlele will be a poinrer to char; the second two will be declared as char. A reference uses the & symbol. But int& means reference to int, &x means address of x, and neither of int& x; int &x; can be interpr…