Path: senator-bedfellow.mit.edu!bloom-beacon.mit.edu!gatech!howland.reston.ans.net!europa.eng.gtefsd.com!uunet!mcsun!sun4nl!tuegate.tue.nl!krait.es.ele.tue.nl!tiggr From: tiggr@es.ele.tue.nl (Tiggr) Newsgroups: comp.lang.objective-c,comp.answers,news.answers Subject: comp.lang.objective-c FAQ, part 3/3: A Sample Program Supersedes: Followup-To: comp.lang.objective-c Date: 17 Aug 1993 10:09:57 GMT Organization: Eindhoven University of Technology Lines: 963 Approved: news-answers-request@mit.edu Expires: 26 Sep 1993 10:09:52 GMT Message-ID: Reply-To: tiggr@es.ele.tue.nl (Tiggr) NNTP-Posting-Host: krait.es.ele.tue.nl Summary: This third part of the comp.lang.objective-c FAQ postings presents a simple sample program written in Objective-C. Originator: tiggr@krait.es.ele.tue.nl Xref: senator-bedfellow.mit.edu comp.lang.objective-c:1505 comp.answers:1640 news.answers:11486 Archive-name: Objective-C/sample Version: $Id: sample.preamble,v 1.6 1993/08/06 12:50:53 tiggr Exp $ A simple sample Objective-C program This is the third part in a series of three informational postings concerning comp.lang.objective-c. This article presents a simple program written in Objective-C. The program consist of several files which are contained in a shar file (see instructions below on how to unpack). The early version of this FAQ was compiled by Bill Shirley, with the aid of many people. The current version is being maintained by Tiggr, aided by a lot of people, including Paul Sanchez and Bill Shirley. Any text in between `[' and `]' is a comment. Comments indicate problems with this FAQ, which should be solved. Send your suggestions, additions, bug reports, comments and fixes to `tiggr@es.ele.tue.nl'. #---------------------------------- cut here ---------------------------------- # This is a shell archive. Remove anything before this line, # then unpack it by saving it in a file and typing "sh file". # # Wrapped by Pieter Schoenmakers on Tue Aug 17 12:04:37 1993 # # This archive contains: # objc-sample # # Existing files will not be overwritten. # Error checking via wc(1) will be performed. LANG=""; export LANG PATH=/bin:/usr/bin:$PATH; export PATH echo mkdir - objc-sample mkdir objc-sample if test -f objc-sample/README then echo Ok to overwrite existing file objc-sample/README\? read answer case "$answer" in [yY]*) echo Proceeding;; *) echo Aborting; exit 1;; esac rm -f objc-sample/README if test -f objc-sample/README then echo Error: could not remove objc-sample/README, aborting exit 1 fi fi echo x - objc-sample/README cat >objc-sample/README <<'@EOF' This directory contains the complete code for the "S[ia]mple Objective-C program" described in comp.lang.objective-c FAQ. If you have a suitable compiler, use the supplied Makefile. Otherwise, program output can be found in the file "output". You should probably read "main.m" first. It is very heavily annotated. Also note and read the file COPYRIGHT. @EOF set `wc -lwc objc-sample/Char.h <<'@EOF' #import @interface Char: Object { int value; } - init: (int) x; - report; @end @EOF set `wc -lwc objc-sample/Node.h <<'@EOF' // Node.h - comp.lang.objective-c simple sample Objective-C program #import @interface Node : Object { id next; id data; } + new: anItem; // create a Node and store anItem in it - free; // free a Node and return the item in it - next; // report the id of the next node after this one - set_next: aNode; // make the next node be aNode @end @EOF set `wc -lwc objc-sample/Node.m <<'@EOF' // Node.m - comp.lang.objective-c simple sample Objective-C program #import #import "Node.h" @implementation Node : Object + new: anItem { self = [super new]; next = 0; data = anItem; return self; } - free { id tmp = data; [super free]; return tmp; } - next { return next; } - set_next: aNode { next = aNode; return self; } @end @EOF set `wc -lwc objc-sample/Queue.h <<'@EOF' // Queue.h - comp.lang.objective-c simple sample Objective-C program #import #import "Node.h" @interface Queue : Object { id head; id tail; unsigned qsize; } + new; // create a new Queue - empty; // clear out all contents of the Queue - put: anItem; // put anItem on the Queue - get; // return the item on top of the Queue - (unsigned) size; // tell us the current size of the Queue @end @EOF set `wc -lwc objc-sample/Queue.m <<'@EOF' // Queue.m - comp.lang.objective-c simple sample Objective-C program #import "Queue.h" @implementation Queue + new { self = [super new]; head = tail = 0; qsize = 0; return self; } - empty { while([self size]) [[self get] free]; return self; } - put: anItem { if (tail) tail = [[tail set_next : [Node new : anItem]] next]; else head = tail = [Node new : anItem]; ++qsize; return self; } - get { id contents; id old_head = head; head = [head next]; contents = [old_head free]; if (--qsize == 0) tail = head; return contents; } - (unsigned) size { return qsize; } @end @EOF set `wc -lwc objc-sample/Stack.h <<'@EOF' // Stack.h - comp.lang.objective-c simple sample Objective-C program #import #import "Node.h" @interface Stack : Object { id stack; unsigned stack_size; } + new; // create a new Stack - empty; // clear out all contents of the Stack - put: anItem; // put anItem on the Stack - get; // return the item on top of the Stack - (unsigned) size; // tell us the current size of the Stack @end @EOF set `wc -lwc objc-sample/Stack.m <<'@EOF' // Stack.m - comp.lang.objective-c simple sample Objective-C program #import "Stack.h" @implementation Stack + new { self = [super new]; stack = 0; stack_size = 0; return self; } - empty { while([self size]) [[self get] free]; return self; } - put: anItem { stack = [[Node new : anItem] set_next : stack]; ++stack_size; return self; } - get { id contents; id old_stack = stack; stack = [stack next]; contents = [old_stack free]; --stack_size; return contents; } - (unsigned) size { return stack_size; } @end @EOF set `wc -lwc objc-sample/output <<'@EOF' Output from demo, excluding Char class: Include the Char class in the demo? (y/n): n queue: 5, stack:-5.0 queue: 4.0, stack: -4 queue: 3, stack:-3.0 queue: 2.0, stack: -2 queue: 1, stack:-1.0 queue: 0.0, stack: 0 queue: -1, stack: 1.0 queue:-2.0, stack: 2 queue: -3, stack: 3.0 queue:-4.0, stack: 4 queue: -5, stack: 5.0 Output from demo, including Char class: Include the Char class in the demo? (y/n): y queue: 5, stack: h queue: q, stack:-4.0 queue: 3, stack: j queue: o, stack:-2.0 queue: 1, stack: l queue: m, stack: 0.0 queue: -1, stack: n queue: k, stack: 2.0 queue: -3, stack: p queue: i, stack: 4.0 queue: -5, stack: r @EOF set `wc -lwc objc-sample/Char.m <<'@EOF' #import #import "Char.h" @implementation Char { int value; } - init: (int) x { [super init]; // In case the parent class is doing // something special in its init... value = x; return self; } - report { printf(" %c", value); return self; } @end @EOF set `wc -lwc objc-sample/Makefile <<'@EOF' # This Makefile assumes you have GNU gcc 2.3 or better and a suitable # runtime library with object support. It also works on a NeXT. Don't know # about Stepstone. .SUFFIXES: .o .m .m.o: $(CC) -c $(CFLAGS) $< # Use this on a NeXT #CC= cc #LIBS= # Use this with GNU CC on a non-NeXT. CC= gcc LIBS= -lobjc CFLAGS= -Wall -O2 -g OFILES= main.o Node.o Queue.o Stack.o Float.o Char.o demo: $(OFILES) $(CC) $(CFLAGS) $(LDFLAGS) -o demo $(OFILES) $(LIBS) clean: rm -f $(OFILES) demo Char.o : Char.m Char.h Float.o : Float.m Float.h Node.o : Node.m Node.h Queue.o : Queue.m Queue.h Node.h Stack.o : Stack.m Stack.h Node.h main.o : main.m Queue.h Node.h Stack.h Float.h @EOF set `wc -lwc objc-sample/Float.m <<'@EOF' #import #import "Float.h" @implementation Float { float value; } - init: (float) x { [super init]; // In case the parent class is doing // something special in its init... value = x; return self; } - report { printf("%4.1f", value); return self; } @end @EOF set `wc -lwc objc-sample/main.m <<'@EOF' // main.m - comp.lang.objective-c simple sample Objective-C program // This is a comment. Everything to the right of a double slash // is ignored. /* * This is too. Objective-C is a superset of ANSI C, * so you don't lose any of your favorite features. */ // Classes are the one real extension which Objective C adds to // ANSI C. A class is a description of a collection of data, like // a C structure, and the methods by which that data may be accessed // or manipulated. Instances of a class are called objects, and // methods are invoked by sending messages to either the class itself, // to produce objects, or to those objects. The recipient of a message // is called a "receiver". The form of a message is: // // [receiver method andMaybeSomeArguments] // // the receiver and method components are mandatory, as are // the square brackets surrounding the message. Additional // arguments may or may not be present, depending upon the // method definition. Messages may appear anywhere a statement // is allowed in C. // The first thing we do is bring in some include files, as in // C. However, we'll use the "import" statement which guarantees // that the file isn't included more than once. #import #import #import "Queue.h" #import "Stack.h" // That brought in class definitions for Objects, Queues, and // Stacks. The Object class is the basis for all other classes, // which is why it gets brought in first. It provides basic functional // behavior which is inherited by all derived classes. All user // created classes should have Object somewhere in their ancestry. // Queue and Stack are classes of our own construction, // and provide FIFO and LIFO storage capabilities, respectively. // I'm not going to go into implementation details here. It's // irrelevant how they work, all that is important is that they // both respond to 'put:' and 'get'. If you want to inspect them, // look into the Queue.m, Stack.m, Queue.h and Stack.h files. // A simple Class definition follows. It inherits // directly from the base class "Object". This gives // it lots of nice properties, not the least of which // is the ability to be referenced by any pointer of the // generic object type "id". All objects can be pointed // to by any id variable, and the default return type from // methods is id. This allows messages to be embedded in // other messages, either as receivers or arguments. // An Int object allocates space for a single integer. // The "report" message causes it to report its value. // Everything between the @implementation and the @end // is part of the class definition. // Note - It is *highly* unusual to have a class implementation // in your main program. Since the object is fully defined before // it gets used, no interface description is required. There is // nothing illegal about doing things this way, but it is so // unusual that the compiler will produce a warning for this class. // We have included the Int class implementation here solely for // expository purposes. @implementation Int: Object // Int is derived from Object { int value; // This is the data portion. Like a struct. } // The following are the method definitions. A "+" prefix means // it is a factory method, i.e., how to manufacture instances of // the class. The body of the method is between braces, like a C // function. // This class doesn't define any factory methods. It relies on the // +alloc method defined in class Object. For examples of factory // methods, look at the +new method defined in the Stack or // Queue implementations. // Self is a special variable, which refers to the object currently // being manipulated. Super refers to the parent class of self. // The following method asks the parent class (Object) to hand us a // new instance, which becomes self. Then we update the instance // variables and return a pointer to the new object. // It is standard for methods that do not need to return any // special value to instead return self. This allows for a // nested syntax of method calls. // The "-" in front of init means that it's an instance method, // i.e., something a particular object should respond to. - init: (int) i // This method will initialize a new Int { [super init]; // In case the parent class is doing // something special in its init... value = i; return self; } - report { printf("%4d", value); return self; } @end // We have implemented Float and Char classes more traditionally, using // separate files for the interface (.h) and implementation (.m). // The Float and Char objects are like the Int object, but with the // obvious difference that they work with floats and characters. // We include the interface definitions at this point. #import "Float.h" #import "Char.h" // If you inspect those files, note polymorphism -- methods have same // names as in the Int class. int main(void) { // First we create instances of "Stack" and "Queue" data structures id queue = [Queue new]; // +new is an older convention for id stack = [Stack new]; // allocation & initialization. // [[x alloc] init] is the preferred // way to do this now. int i; int reply; fprintf(stderr, "Include the Char class in the demo? (y/n): "); reply = getchar(); // no error checking... for (i = 5; i > -6; --i) { // Depending on which version of the demo we're running, // we alternate putting Int's and Floats onto the queue and // stack, or Int's, Float's, and Char's. if (reply == 'y') { // If "i" is odd we put an Int on the queue and a Char on // the stack. If "i" is even we put an Char on the queue // and a Float on the stack. // Since there is more than one method "init", and // Objective-C uses run-time binding, the compiler doesn't // know what the type of the object returned by alloc. // We disambiguate with an explicit C-style cast to make // sure the appropriate "init" is invoked. [queue put: (i & 1) ? [(Int*)[Int alloc] init: i] : [(Char*)[Char alloc] init: 'm'+i]]; [stack put: (i & 1) ? [(Char*)[Char alloc] init: 'm'+i] : [(Float*)[Float alloc] init: i]]; } else // Note - garbage input will invoke the else clause. { // If "i" is odd we put an Int on the queue and a Float on // the stack. If "i" is even we put a Float on the queue // and an Int on the stack. [queue put: (i & 1) ? [(Int*)[Int alloc] init: i] : [(Float*)[Float alloc] init: i]]; [stack put: (i & 1) ? [(Float*)[Float alloc] init: i] : [(Int*)[Int alloc] init: i]]; } } while ([queue size] && [stack size]) { // The following illustrates run-time binding. Will report be // invoked for a Float object or an Int object? Did the user // elect for Char objects at run time? We don't know ahead // of time, but with run-time binding and polymorphism // it works properly. The burden is on the class // implementer rather than the class user. // Note that the following lines remain unchanged, whether // we are using the Char class or not. The queue and stack // hand us the next object, it reports itself regardless // of its type, and then it frees itself. printf("queue:"); [[[queue get] report] free]; printf(", stack:"); [[[stack get] report] free]; putchar('\n'); } return 0; } @EOF set `wc -lwc objc-sample/COPYRIGHT <<'@EOF' This copyright notice applies to all source files distributed in the comp.lang.objective-c FAQ: `A simple sample Objective-C program'. Copyright (C) 1993 Paul J. Sanchez and Bill Shirley The `simple sample Objective-C program' is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation; either version 2, or (at your option) any later version. The `simple sample Objective-C program' is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with GNU Emacs; see the file COPYING. If not, write to the Free Software Foundation, 675 Mass Ave, Cambridge, MA 02139, USA. @EOF set `wc -lwc objc-sample/Float.h <<'@EOF' #import @interface Float: Object { float value; } - init: (float) x; - report; @end @EOF set `wc -lwc