comp.lang.objective-c FAQ, part 3/3: A Sample Program
Pieter Schoenmakers
Version: $Id: sample.preamble,v 3.12 1998/04/20 12:52:25 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). [Note,
from version 2.3 of this file, the sample has been changed in order to
reduce the number of compiler warnings (down to 1, which is in there for
explanatory purposes) and to reflect the use of `+alloc' and `-init' instead
of `+new'.]
The early version of this FAQ was compiled by Bill Shirley, with the aid of
many people. The current version is being maintained by Pieter Schoenmakers
<ti...@gerbil.org>, aided by a lot of people, including Paul Sanchez and
Bill Shirley.
A World Wide Web hypertext version of this FAQ is maintained by Steve Dekorte
<dek...@suite.com> at http://www.slip.net/~dekorte/Objective-C/.
A Japanese language version of this FAQ, maintained by Norihiro Itoh
<ni...@fsinet.or.jp>, resides at http://www.fsinet.or.jp/~nito/index-j.html.
Send your suggestions, additions, bug reports, comments and fixes to
`ti...@gerbil.org'.
#---------------------------------- 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 <tiggr@akebono> on Thu Sep 17 14:51:13 1998
#
# 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:/usr/sbin:/usr/ccs/bin:$PATH; export PATH
echo mkdir - objc-sample
mkdir objc-sample
if test -f objc-sample/Char.h
then
echo Ok to overwrite existing file objc-sample/Char.h\?
read answer
case "$answer" in
[yY]*) echo Proceeding;;
*) echo Aborting; exit 1;;
esac
rm -f objc-sample/Char.h
if test -f objc-sample/Char.h
then
echo Error: could not remove objc-sample/Char.h, aborting
exit 1
fi
fi
echo x - objc-sample/Char.h
cat >objc-sample/Char.h <<'__EOF__'
#import <objc/Object.h>
@interface Char: Object
{
int value;
}
-init: (int) x;
-report;
@end
__EOF__
set `wc -lwc <objc-sample/Char.h`
if test $1$2$3 != 111498
then
echo ERROR: wc results of objc-sample/Char.h are $* should be 11 14 98
fi
chmod 644 objc-sample/Char.h
if test -f objc-sample/Char.m
then
echo Ok to overwrite existing file objc-sample/Char.m\?
read answer
case "$answer" in
[yY]*) echo Proceeding;;
*) echo Aborting; exit 1;;
esac
rm -f objc-sample/Char.m
if test -f objc-sample/Char.m
then
echo Error: could not remove objc-sample/Char.m, aborting
exit 1
fi
fi
echo x - objc-sample/Char.m
cat >objc-sample/Char.m <<'__EOF__'
#import <stdio.h>
#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/Char.m`
if test $1$2$3 != 2347279
then
echo ERROR: wc results of objc-sample/Char.m are $* should be 23 47 279
fi
chmod 644 objc-sample/Char.m
if test -f objc-sample/Float.h
then
echo Ok to overwrite existing file objc-sample/Float.h\?
read answer
case "$answer" in
[yY]*) echo Proceeding;;
*) echo Aborting; exit 1;;
esac
rm -f objc-sample/Float.h
if test -f objc-sample/Float.h
then
echo Error: could not remove objc-sample/Float.h, aborting
exit 1
fi
fi
echo x - objc-sample/Float.h
cat >objc-sample/Float.h <<'__EOF__'
#import <objc/Object.h>
@interface Float: Object
{
float value;
}
-initFloatValue: (float) x;
-report;
@end
__EOF__
set `wc -lwc <objc-sample/Float.h`
if test $1$2$3 != 1114113
then
echo ERROR: wc results of objc-sample/Float.h are $* should be 11 14 113
fi
chmod 644 objc-sample/Float.h
if test -f objc-sample/Float.m
then
echo Ok to overwrite existing file objc-sample/Float.m\?
read answer
case "$answer" in
[yY]*) echo Proceeding;;
*) echo Aborting; exit 1;;
esac
rm -f objc-sample/Float.m
if test -f objc-sample/Float.m
then
echo Error: could not remove objc-sample/Float.m, aborting
exit 1
fi
fi
echo x - objc-sample/Float.m
cat >objc-sample/Float.m <<'__EOF__'
#import <stdio.h>
#import "Float.h"
@implementation Float
{
float value;
}
-initFloatValue: (float) x
{
[super init];
value = x;
return self;
}
-report
{
printf ("%4.1f", value);
return self;
}
@end
__EOF__
set `wc -lwc <objc-sample/Float.m`
if test $1$2$3 != 2231215
then
echo ERROR: wc results of objc-sample/Float.m are $* should be 22 31 215
fi
chmod 644 objc-sample/Float.m
if test -f objc-sample/Makefile
then
echo Ok to overwrite existing file objc-sample/Makefile\?
read answer
case "$answer" in
[yY]*) echo Proceeding;;
*) echo Aborting; exit 1;;
esac
rm -f objc-sample/Makefile
if test -f objc-sample/Makefile
then
echo Error: could not remove objc-sample/Makefile, aborting
exit 1
fi
fi
echo x - objc-sample/Makefile
cat >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,
# and avoid the GCC moaning on using #import.
CC= gcc -Wno-import
LIBS= -lobjc
LDFLAGS= -L/usr/local/lib -L/usr/gnu/lib
CFLAGS= -Wall -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/Makefile`
if test $1$2$3 != 37127783
then
echo ERROR: wc results of objc-sample/Makefile are $* should be 37 127 783
fi
chmod 644 objc-sample/Makefile
if test -f objc-sample/Node.h
then
echo Ok to overwrite existing file objc-sample/Node.h\?
read answer
case "$answer" in
[yY]*) echo Proceeding;;
*) echo Aborting; exit 1;;
esac
rm -f objc-sample/Node.h
if test -f objc-sample/Node.h
then
echo Error: could not remove objc-sample/Node.h, aborting
exit 1
fi
fi
echo x - objc-sample/Node.h
cat >objc-sample/Node.h <<'__EOF__'
#import <objc/Object.h>
@interface Node : Object
{
id next;
id data;
}
-init: 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
-setNext: aNode; // make the next node be aNode
@end
__EOF__
set `wc -lwc <objc-sample/Node.h`
if test $1$2$3 != 1456295
then
echo ERROR: wc results of objc-sample/Node.h are $* should be 14 56 295
fi
chmod 644 objc-sample/Node.h
if test -f objc-sample/Node.m
then
echo Ok to overwrite existing file objc-sample/Node.m\?
read answer
case "$answer" in
[yY]*) echo Proceeding;;
*) echo Aborting; exit 1;;
esac
rm -f objc-sample/Node.m
if test -f objc-sample/Node.m
then
echo Error: could not remove objc-sample/Node.m, aborting
exit 1
fi
fi
echo x - objc-sample/Node.m
cat >objc-sample/Node.m <<'__EOF__'
#import <objc/Object.h>
#import "Node.h"
@implementation Node: Object
-init: anItem
{
self = [super init];
next = 0;
data = anItem;
return self;
}
-free
{
id tmp = data;
[super free];
return tmp;
}
-next
{
return next;
}
-setNext: aNode
{
next = aNode;
return self;
}
@end
__EOF__
set `wc -lwc <objc-sample/Node.m`
if test $1$2$3 != 3249299
then
echo ERROR: wc results of objc-sample/Node.m are $* should be 32 49 299
fi
chmod 644 objc-sample/Node.m
if test -f objc-sample/Queue.h
then
echo Ok to overwrite existing file objc-sample/Queue.h\?
read answer
case "$answer" in
[yY]*) echo Proceeding;;
*) echo Aborting; exit 1;;
esac
rm -f objc-sample/Queue.h
if test -f objc-sample/Queue.h
then
echo Error: could not remove objc-sample/Queue.h, aborting
exit 1
fi
fi
echo x - objc-sample/Queue.h
cat >objc-sample/Queue.h <<'__EOF__'
#import <objc/Object.h>
#import "Node.h"
@interface Queue: Object
{
id head;
id tail;
unsigned qsize;
}
-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 int) size; // tell us the current size of the Queue
@end
__EOF__
set `wc -lwc <objc-sample/Queue.h`
if test $1$2$3 != 1655319
then
echo ERROR: wc results of objc-sample/Queue.h are $* should be 16 55 319
fi
chmod 644 objc-sample/Queue.h
if test -f objc-sample/Queue.m
then
echo Ok to overwrite existing file objc-sample/Queue.m\?
read answer
case "$answer" in
[yY]*) echo Proceeding;;
*) echo Aborting; exit 1;;
esac
rm -f objc-sample/Queue.m
if test -f objc-sample/Queue.m
then
echo Error: could not remove objc-sample/Queue.m, aborting
exit 1
fi
fi
echo x - objc-sample/Queue.m
cat >objc-sample/Queue.m <<'__EOF__'
#import "Queue.h"
@implementation Queue
-empty
{
while([self size])
[[self get] free];
return self;
}
-put: anItem
{
if (tail)
tail = [[tail setNext : [[Node alloc] init: anItem]] next];
else
head = tail = [[Node alloc] init: 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/Queue.m`
if test $1$2$3 != 3975486
then
echo ERROR: wc results of objc-sample/Queue.m are $* should be 39 75 486
fi
chmod 644 objc-sample/Queue.m
if test -f objc-sample/README
then
echo Ok to overwrite existing file objc-sample/README\?
read answer
case "$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 "Simple Sample Objective-C
program" described in the 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/README`
if test $1$2$3 != 855366
then
echo ERROR: wc results of objc-sample/README are $* should be 8 55 366
fi
chmod 644 objc-sample/README
if test -f objc-sample/Stack.h
then
echo Ok to overwrite existing file objc-sample/Stack.h\?
read answer
case "$answer" in
[yY]*) echo Proceeding;;
*) echo Aborting; exit 1;;
esac
rm -f objc-sample/Stack.h
if test -f objc-sample/Stack.h
then
echo Error: could not remove objc-sample/Stack.h, aborting
exit 1
fi
fi
echo x - objc-sample/Stack.h
cat >objc-sample/Stack.h <<'__EOF__'
#import <objc/Object.h>
#import "Node.h"
@interface Stack: Object
{
id stack;
unsigned int stack_size;
}
-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.h`
if test $1$2$3 != 1553318
then
echo ERROR: wc results of objc-sample/Stack.h are $* should be 15 53 318
fi
chmod 644 objc-sample/Stack.h
if test -f objc-sample/Stack.m
then
echo Ok to overwrite existing file objc-sample/Stack.m\?
read answer
case "$answer" in
[yY]*) echo Proceeding;;
*) echo Aborting; exit 1;;
esac
rm -f objc-sample/Stack.m
if test -f objc-sample/Stack.m
then
echo Error: could not remove objc-sample/Stack.m, aborting
exit 1
fi
fi
echo x - objc-sample/Stack.m
cat >objc-sample/Stack.m <<'__EOF__'
#import "Stack.h"
@implementation Stack
-empty
{
while([self size])
[[self get] free];
return self;
}
-put: anItem
{
stack = [[[Node alloc] init: anItem] setNext : 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/Stack.m`
if test $1$2$3 != 3557407
then
echo ERROR: wc results of objc-sample/Stack.m are $* should be 35 57 407
fi
chmod 644 objc-sample/Stack.m
if test -f objc-sample/main.m
then
echo Ok to overwrite existing file objc-sample/main.m\?
read answer
case "$answer" in
[yY]*) echo Proceeding;;
*) echo Aborting; exit 1;;
esac
rm -f objc-sample/main.m
if test -f objc-sample/main.m
then
echo Error: could not remove objc-sample/main.m, aborting
exit 1
fi
fi
echo x - objc-sample/main.m
cat >objc-sample/main.m <<'__EOF__'
/* main.m - comp.lang.objective-c simple sample Objective-C program. */
// This is a comment, just like the previous line. Everything to the right
// of a double slash is ignored.
/* Classes are the one real extension which Objective-C adds to 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. On the
NeXT, it is customary to use the "import" statement which guarantees that
the file isn't included more than once. Using GNU CC this is not all
that nice sinds it generates a huge warning for every file being
compiled. So, since it does not really matter, we'll stick to
`#include'. */
#import <stdio.h>
#import <objc/Object.h>
#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 normally 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. The Int class implementation is 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
{
/* Have our superclass initialize its part of us. After that,
initialize the part of us introduced by this class (Int). */
[super 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 create instances of "Stack" and "Queue" data structures. */
id queue = [[Queue alloc] init];
id stack = [[Stack alloc] init];
int i, reply;
fprintf (stderr, "Include the Char class in the demo? (y/n): ");
/* Anything not matching `y.*' means no. */
reply = getchar ();
for (i = 5; i > -6; --i)
{
/* Depending on which version of the demo we're running, we
alternately put Ints and Floats onto the queue and stack, or
Ints, Floats, and Chars. */
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 since
`+alloc' returns a plain, typeless, `id', the compiler
doesn't know the type of the object returned by alloc. An
explicit cast (i.e. static type indication) ensures that the
compiler knows which `init:' is invoked---the one accepting a
char or the other one accepting an int.
Another solution, which avoids the static type indication, is
to put typing information on the method in the method's name.
This is done for the Float class. */
id my_char = [(Char *) [Char alloc] init: 'm' + i];
if (i & 1)
{
[queue put: [(Int *) [Int alloc] init: i]];
[stack put: my_char];
}
else
{
[queue put: my_char];
[stack put: [[Float alloc] initFloatValue: i]];
}
}
else
{
/* 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 alloc] initFloatValue: i])];
[stack put: ((i & 1)
? [[Float alloc] initFloatValue: 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/main.m`
if test $1$2$3 != 19612587741
then
echo ERROR: wc results of objc-sample/main.m are $* should be 196 1258 7741
fi
chmod 644 objc-sample/main.m
if test -f objc-sample/output
then
echo Ok to overwrite existing file objc-sample/output\?
read answer
case "$answer" in
[yY]*) echo Proceeding;;
*) echo Aborting; exit 1;;
esac
rm -f objc-sample/output
if test -f objc-sample/output
then
echo Error: could not remove objc-sample/output, aborting
exit 1
fi
fi
echo x - objc-sample/output
cat >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/output`
if test $1$2$3 != 29111679
then
echo ERROR: wc results of objc-sample/output are $* should be 29 111 679
fi
chmod 644 objc-sample/output
if test -f objc-sample/COPYRIGHT
then
echo Ok to overwrite existing file objc-sample/COPYRIGHT\?
read answer
case "$answer" in
[yY]*) echo Proceeding;;
*) echo Aborting; exit 1;;
esac
rm -f objc-sample/COPYRIGHT
if test -f objc-sample/COPYRIGHT
then
echo Error: could not remove objc-sample/COPYRIGHT, aborting
exit 1
fi
fi
echo x - objc-sample/COPYRIGHT
cat >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
Copyright (C) 1994, 1996 Pieter J. Schoenmakers
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, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
__EOF__
set `wc -lwc <objc-sample/COPYRIGHT`
if test $1$2$3 != 19155973
then
echo ERROR: wc results of objc-sample/COPYRIGHT are $* should be 19 155 973
fi
chmod 644 objc-sample/COPYRIGHT
chmod 755 objc-sample
exit 0