TweetFollow Us on Twitter

Digging in to Objective-C

Volume Number: 19 (2003)
Issue Number: 2
Column Tag: Getting Started

Digging in to Objective-C

by Dave Mark

In this month's column, we're going to start our foray into Objective-C. Before we do that, however, let's make sure we're on the same page, tools-wise.

Got the Latest Tools?

If you haven't already, login to http://developer.apple.com/ and download the December 2002 Mac OS X Developer Tools. Note that the download is 301.2 MB so maybe let this one run during your lunch break. Note that the December 2002 Tools will only run on 10.2 or later. If you need to run on an earlier OS, stick with the April 2002 Tools.

Once your download is complete, you'll have a very large file named Dec2002DevToolsCD.dmg. Double-click this. The disk image that mounts will contain a file named Developer.mpkg. This master package will install all the packages in the Packages folder. No need to install these separately.

The install will take a while. Be patient. There's a lot of stuff here. Here's a list of the packages that will be installed as part of this process:

    - Developer Tools (DevTools.pkg)

    - Mac OS X SDK (DevSDK.pkg)

    - Developer Documentation (DevDocumentation.pkg)

    - Developer Examples (DevExamples.pkg)

    - SDK pieces for UNIX development (BSDSDK.pkg)

    - A package with extra pieces needed for Project Builder-emacs integration (Dec2002DevToolsExtras.pkg)

If your setup was the same as mine, you were running Project Builder 2.0.1 and are now running Project Builder 2.1. This is from the Project Builder 2.1 section in the file What's New.pdf:

    - Support for external editors:

    * You can use arbitrary editors for different file types.

    * Project Builder will show you build errors in your external editor when you use BBEdit or emacs.

    - Build system features:

    * Project Builder will now do multiple compiles at the same time on machines with more than one processor.

    * Project Builder's header dependency analysis is improved.

    * Project Builder now links executables in a more optimal manner.

    * You can now set compile flags on a per-file basis.

    * Assembler flags are now separate from flags to the compiler.

    - Interface to customize key bindings.

    - Better CVS integration.

    - The CodeWarrior project importer has been vastly improved.

    - Miscellaneous interface improvements:

    * You can now sort files, targets, and build phase objects in a project.

    * You can display line numbers on the same line as your source.

    * The breakpoint gutter has been improved.

    - JavaDoc documentation is now indexed so that it can be used with Project Builder's integrated documentation.

    - Improved text encoding support.

    - There is support for dynamic C++ types in the debugger.

In addition, here's the non-Project Builder specific stuff:

    * gcc3.1 has several bug fixes. In addition:

    - an optimization has been made to speed up searching for header files. If your command lines have a lot of -I directives to add directories to the compiler's search path, this optimization should help your compile time.

    - The HTML documentation for the compiler is missing from the release. You can find it on the web at:

    http://developer.apple.com/techpubs/macosx/DeveloperTools/gcc3/gcc/index.html

    http://developer.apple.com/techpubs/macosx/DeveloperTools/gcc3/cpp/index.html

    * AppleScript Studio 1.2.1 adds enhanced dictionary support. The sample projects will now run on both Mac OS X 10.1 systems as well as Mac OS X 10.2. Please read the AppleScript Studio release notes for more information.

    * CHUD 2.5.1 is now on the CD. CHUD is a set of tools for low-level system debugging and profiling. To install, open the disk image, and follow the instructions.

    * !AppleScript Editor 2.0 Beta is now available in the Pre-release Software folder. Please read the "About These Packages.rtf" file in the Pre-release Software folder for more details. Note that this package requires Mac OS X 10.2.3 or higher.

    * The jikes Java compiler has been updated to version 1.17.

    * PackageMaker has some new features:

    - Drag-and-drop functionality in the list editor.

    - Inline attribute editing.

    - Progress sheet for status during package creation.

    - Package completion dialog.

    * Sherlock SDK - There is now an SDK available to develop your own Sherlock channels. See

    /Developer/Examples/Sherlock for sample channels and the online documentation for more information.

    * DiscRecording SDK - There are now sample projects demonstrating the DiscRecording framework. Please see: /Developer/Examples/DiscRecording/About Disc Recording Examples.rtf for more information.

    * CoreAudio SDK - There are more examples in /Developer/Examples/CoreAudio. Please see /Developer/Examples/CoreAudio/ReadMe.rtf for more information.

    * FireWire SDK - There is now a complete SDK for developing for FireWire devices. Please see

    /Developer/Examples/IOKit/firewire for the samples.

    * ForceFeedback SDK - The header files necessary to take advantage of Mac OS X 10.2.3's ForceFeedback framework have been added.

    * AvailabilityMacros - You can now control which OS version you want to target your application for using the AvailabilityMacros. Please see

    /Developer/Documentation/ReleaseNotes/AvailabilityMacros.h for more details.

    * New and updated documentation. Lots of new documentation content is included in this release. Please check the various "what's new" portions of the documentation for more information.

When you launch Project Builder 2.1 for the first time, the release notes window appears. You can bring this window up again at any time by selecting Show Release Notes from Project Builder's Help menu.

On to Objective-C...

OK. Now that we're all using the same tools, let's dig into our main course. Objective-C is based on the C programming language. In effect, it is C with objects. Though there are many differences between Objective-C and C++, the main difference lies in the dynamic nature of Objective-C.

C++ requires static dispatch, static typing, and static loading. Objective-C offers dynamic dispatch, dynamic typing, and dynamic loading. In a nutshell, static dispatch means the decision of which object receives which message happens at compile-time, while dynamic dispatch means the decision is delayed until run-time.

Same thing with typing and loading. When the type of the message receiver can be determined at run-time, that's dynamic typing. When code can be linked and executed at run-time as opposed to at compile-time, that's dynamic loading.

To me, all three of these concepts are very tightly intertwined. A static approach offers the safety of forcing a lot of problems to the surface at compile-time. Don't be lulled into a false sense of security, however. Just because your code compiles doesn't mean your code isn't riddled with errors. It just means that your code conforms, at a basic level, to the language syntax enforced by the compiler. But static typing, for example, clearly offers a certain level of safety not afforded by dynamic typing.

The dynamic approach jettisons the static safety net in exchange for incredible flexibility and freedom. Dynamic loading means you can deliver a new suite of objects to your customer over the net, and have the code installed, all while the existing app is still up and running. Imagine the possibilities. You could fix a bug on a mission-critical program without having to shut it down. If you knew the protocol, you could even patch someone else's program, replacing their inferior object with one of your own design.

To be fair to C++, there is a certain element of risk in a completely dynamic approach. But with this risk comes great potential reward. Whichever side of the dynamic/static argument you come down on, there is no downside to learning and understanding Objective-C. If you understand the benefits of Objective-C, you can make an informed choice between it and C++. And the cool thing is, with Objective-C, you can still use static typing when you choose to (to make an element of your code clearer to others, for example). With Objective-C, you get the best of both worlds.

If all this seems a little vague, not to worry. Over time, as we dig into more and more code, these concepts will fall into place. Let's take a look at an example.

Employee: The C++ Version

To start things off, here's a relatively simple C++ program (lifted and slightly modified from Learn C++ on the Macintosh, with permission from the author!) that we'll translate into Objective-C. We're going to define a class named Employee, then create and destroy a couple of Employee instances.

Want to follow along in Project Builder? Create a new project, and select "C++ Tool" from the "Tool" category when prompted for the type of project to build. Now select New File from the File menu and choose "C++ Class" from the "Carbon" category. You'll call the new class "Employee". Project Builder will create two new files (assuming you checked the "Also create Employee.h" checkbox) and add them to your project. All you need to do is replace the contents of Employee.h, Employee.cpp, and main.cpp with the code below.

    Got a net connection? Rather download the code than type it in? We're working on adding the code downloads to the MacTech web site. If that is not up and running by the time you read this, head over to http://www.spiderworks.com and download the code from there. I'll put both the C++ and Objective-C versions up for your downloading pleasure.

Here's Employee.h:

class Employee
{
//         Data members...
   private:
      char   employeeName[ 20 ];
      long   employeeID;
      float   employeeSalary;
//         Member functions...
   public:
            Employee( char *name, long id, float salary );
            ~Employee( void );
      void   PrintEmployee( void );
};

Here's Employee.cpp:

#include <iostream>
#include "employee.h"
Employee::Employee( char *name, long id, float salary )
{
    strcpy( this->employeeName, name );
    this->employeeID = id;
    this->employeeSalary = salary;
    
    std::cout << "Creating employee #"
                           << employeeID << "\n";
}
Employee::~Employee( void )
{
    std::cout << "Deleting employee #"
                           << employeeID << "\n";
}
void   Employee::PrintEmployee( void )
{
    std::cout << "-----\n";
    std::cout << "Name:   " << employeeName << "\n";
    std::cout << "ID:     " << employeeID << "\n";
    std::cout << "Salary: " << employeeSalary << "\n";
    std::cout << "-----\n";
}

Finally, here's main.cpp:

#include <iostream>
#include "employee.h"
int main (int argc, const char * argv[])
{
    Employee   employee1( "Frank Zappa", 1, 200.0 );
    Employee   employee2( "Donald Fagen", 2, 300.0 );
    employee1.PrintEmployee();
    employee2.PrintEmployee();
}

Once all the code is typed in, give it a run and compare your results to those shown in Figure 1. If you compare the results with the code in main.cpp, you'll see that the first two lines are produced as the two Employee objects are created, the next two chunks (5 lines each) are produced by the two calls to PrintEmployee(), and the two "Deleting" lines are produced when the program exits and the objects are destroyed.


Figure 1. The C++ version of Employee in action.

The Employee object is fairly straight-forward. Looking at the code in Employee.cpp, you'll see that the constructor uses its arguments to initialize the data members of the Employee object, then uses cout to send a message letting us know the object is being created. The destructor also uses cout to let us know its object is being destroyed. And PrintEmployee() uses cout to print some useful info as well.

Pretty straight-forward, right? Now let's create an Objective-C program to do the same thing.

Employee: The Objective-C Version

In Project Builder, select New Project... from the File menu. This time, select "Foundation Tool" from the Tool category. Now select New File... from the File menu and choose Objective-C Class from the Cocoa category. Name the new file Employee.m and be sure the "Also create Employee.h" checkbox is checked.

As you did with your C++ project, now you'll replace the contents of Employee.h, Employee.m, and main.m with the code below. Here's Employee.h:

#import <Foundation/Foundation.h>
@interface Employee : NSObject {
    @private
        char      employeeName[20];
        long      employeeID;
        float      employeeSalary;
}
- (id)initWithName:(char *)name andID:(long)id
    andSalary:(float)salary;
- (void)PrintEmployee;
- (void)dealloc;
@end

Here's Employee.m:

#import "Employee.h"
@implementation Employee
    - (id)initWithName:(char *)name andID:(long)id
                            andSalary:(float)salary {
        strcpy( employeeName, name );
        employeeID = id;
        employeeSalary = salary;
        
        printf( "Creating employee #%ld\n", employeeID );
        
        return self;
    }
    
    - (void)PrintEmployee {
        printf( "----\n" );
        printf( "Name:   %s\n", employeeName );
        printf( "ID:     %ld\n", employeeID );
        printf( "Salary: %5.2f\n", employeeSalary );
        printf( "----\n" );
    }
    - (void)dealloc {
        
        printf( "Deleting employee #%ld\n", employeeID );
        
        [super dealloc];
    }
@end

and here's main.m:

#import <Foundation/Foundation.h>
#import "Employee.h"
int main (int argc, const char * argv[]) {
    NSAutoreleasePool * pool =
                        [[NSAutoreleasePool alloc] init];
    Employee*   employee1 = [[Employee alloc] initWithName:"Frank Zappa" andID:1 andSalary:200];
    Employee*   employee2 = [[Employee alloc] initWithName:"Donald Fagen" andID:2 andSalary:300];
    [employee1 PrintEmployee];
    [employee2 PrintEmployee];
    
    [employee1 release];
    [employee2 release];
    
    [pool release];
    return 0;
}

As you did before, run the project. This time, compare your results with Figure 2. Look familiar? The Salary field looks a bit different but, other than that, the results are identical.


Figure 2. The results of the Objective C version of Employee.

Till Next Month...

Take some time and look at the Objective-C and C++ code side-by-side. You should be able to tell a lot about the Objective-C code just from this context. In next month's column, we're going to dissect the Objective-C code, line-by-line. Till then, here's some food for thought:

In C++ you call a member function. In Objective-C you send a message to a receiver. For example, in C++ you might use an object pointer to say:

myObj->changeValue;

In Objective-C you'd say:

[myObj changeValue];

Objective-C classes are, like their C++ counterparts, broken into an interface (the ".h" file) and an implementation (the ".m" file). Instance methods start with a "-" character in the interface, class methods start with a "+".The type "id" is Objective C's generic object pointer type. You'll see it a lot.

(id)myFunc; declares a function named myFunc that returns an id pointer.

(id)getP:(int)p; declares a function named getP: that takes a parameter p of type int. The colon at the end of the function name indicates that the function takes a parameter.

(id)getP:(int)p andQ:(long)q declares a function named getP:andQ: taking two params - an int named p and a long named q.

Look through the code, think about what's happening, see you back here next month...


Dave Mark is very old. He's been hanging around with Apple since before there was electricity and has written a number of books on Macintosh development, including Learn C on the Macintosh, Learn C++ on the Macintosh, and The Macintosh Programming Primer series. Check out Dave's web site at http://www.spiderworks.com

 

Community Search:
MacTech Search:

Software Updates via MacUpdate

Box Sync 4.0.6567 - Online synchronizati...
Box Sync gives you a hard-drive in the Cloud for online storage. Note: You must first sign up to use Box. What if the files you need are on your laptop -- but you're on the road with your iPhone? No... Read more
Carbon Copy Cloner 4.1.4 - Easy-to-use b...
Carbon Copy Cloner backups are better than ordinary backups. Suppose the unthinkable happens while you're under deadline to finish a project: your Mac is unresponsive and all you hear is an ominous,... Read more
OmniGraffle Pro 6.3.1 - Create diagrams,...
OmniGraffle Pro helps you draw beautiful diagrams, family trees, flow charts, org charts, layouts, and (mathematically speaking) any other directed or non-directed graphs. We've had people use... Read more
Monosnap 3.1.2 - Versatile screenshot ut...
Monosnap lets you capture screenshots, share files, and record video and .gifs! Capture: Capture full screen, just part of the screen, or a selected window Make your crop area pixel perfect with... Read more
Alfred 2.7.2 - Quick launcher for apps a...
Alfred is an award-winning productivity application for OS X. Alfred saves you time when you search for files online or on your Mac. Be more productive with hotkeys, keywords, and file actions at... Read more
Microsoft Remote Desktop 8.0.19 - Connec...
With Microsoft Remote Desktop, you can connect to a remote PC and your work resources from almost anywhere. Experience the power of Windows with RemoteFX in a Remote Desktop client designed to help... Read more
OmniGraffle 6.3 - Create diagrams, flow...
OmniGraffle helps you draw beautiful diagrams, family trees, flow charts, org charts, layouts, and (mathematically speaking) any other directed or non-directed graphs. We've had people use Graffle to... Read more
PDFKey Pro 4.3.2 - Edit and print passwo...
PDFKey Pro can unlock PDF documents protected for printing and copying when you've forgotten your password. It can now also protect your PDF files with a password to prevent unauthorized access and/... Read more
Ableton Live 9.2.2 - Record music using...
Ableton Live lets you create and record music on your Mac. Use digital instruments, pre-recorded sounds, and sampled loops to arrange, produce, and perform your music like never before. Ableton Live... Read more
Macs Fan Control 1.3.1.0 - Monitor and c...
Macs Fan Control allows you to monitor and control almost any aspect of your computer's fans, with support for controlling fan speed, temperature sensors pane, menu-bar icon, and autostart with... Read more

This Week at 148Apps: August 24-28, 2015
The Apps of August With 148Apps How do you know what apps are worth your time and money? Just look to the review team at 148Apps. We sort through the chaos and find the apps you're looking for. The ones we love become Editor’s Choice, standing out... | Read more »
NASCAR in Real Racing 3? Sure, Why Not?
I have to give Firemonkeys credit - it's very cool of them to add NASCAR to Real Racing 3 via an update rather than making a separate game for it. But that's a different discussion for another time; for now let's sit back and enjoy driving in... | Read more »
The nuyu is an Inexpensive Activity Moni...
Today, Health o Meter nuyu has announced a series of health and fitness-related products, including the aforementioned activity monitor along with a wireless scale. All at a decent pricepoint, no less. [Read more] | Read more »
The Makers of Overkill are Trying Someth...
Craneballs, the studio responsible for the Overkill series, is taking a little break from all that violence (a little break) to bring us Cube Worm - a 3D take on one of the most classic PC/calculator games in existence. [Read more] | Read more »
The Sandbox Welcomes Cutethulu in its La...
Another month, another update to Pixowl's The Sandbox. This time players can say hello to "Cutethulu" - an adorable little rendition of perhaps the most well known (and infamous) of the Elder Gods. [Read more] | Read more »
ReBoard: Revolutionary Keyboard (Utilit...
ReBoard: Revolutionary Keyboard 1.0 Device: iOS Universal Category: Utilities Price: $1.99, Version: 1.0 (iTunes) Description: Do everything within the keyboard without switching apps! If you are in WhatsApp, how do you schedule a... | Read more »
Tiny Empire (Games)
Tiny Empire 1.1.3 Device: iOS Universal Category: Games Price: $2.99, Version: 1.1.3 (iTunes) Description: Launch cannonballs and blow tiny orcs into thousands of pieces in this intuitive fantasy-themed puzzle shooter! Embark on an... | Read more »
Astropad Mini (Productivity)
Astropad Mini 1.0 Device: iOS iPhone Category: Productivity Price: $4.99, Version: 1.0 (iTunes) Description: *** 50% off introductory price! ​*** Get the high-end experience of a Wacom tablet at a fraction of the price with Astropad... | Read more »
Emo Chorus (Music)
Emo Chorus 1.0.0 Device: iOS Universal Category: Music Price: $1.99, Version: 1.0.0 (iTunes) Description: Realistic Choir simulator ranging from simple Chorus emulation to full ensemble Choir with 128 members. ### introductory offer... | Read more »
Forest Spirit (Games)
Forest Spirit 1.0.5 Device: iOS Universal Category: Games Price: $2.99, Version: 1.0.5 (iTunes) Description: | Read more »

Price Scanner via MacPrices.net

WaterField Designs Unveils American-Made, All...
San Francisco’s WaterField Designs today unveiled their all-leather Cozmo 2.0 — an elegant attach laptop bag with carefully-designed features to suit any business environment. The Cozmo 2.0 is... Read more
Apple’s 2015 Back to School promotion: Free B...
Purchase a new Mac or iPad at The Apple Store for Education and take up to $300 off MSRP. All teachers, students, and staff of any educational institution qualify for the discount. Shipping is free,... Read more
128GB MacBook Airs on sale for $100 off MSRP,...
B&H Photo has 11″ & 13″ MacBook Airs with 128GB SSDs on sale for $100 off MSRP. Shipping is free, and B&H charges NY sales tax only: - 11″ 1.6GHz/128GB MacBook Air: $799.99, $100 off MSRP... Read more
13-inch 2.5GHz MacBook Pro (refurbished) avai...
The Apple Store has Apple Certified Refurbished 13″ 2.5GHz MacBook Pros available for $829, or $270 off the cost of new models. Apple’s one-year warranty is standard, and shipping is free: - 13″ 2.... Read more
27-inch 3.2GHz iMac on sale for $1679, save $...
B&H Photo has the 27″ 3.2GHz iMac on sale for $1679.99 including free shipping plus NY sales tax only. Their price is $120 off MSRP. Read more
Apple and Cisco Partner to Deliver Fast-Lane...
Apple and Cisco have announced a partnership to create a “fast lane” for iOS business users by optimizing Cisco networks for iOS devices and apps. The alliance integrates iPhone with Cisco enterprise... Read more
Apple offering refurbished 2015 13-inch Retin...
The Apple Store is offering Apple Certified Refurbished 2015 13″ Retina MacBook Pros for up to $270 (15%) off the cost of new models. An Apple one-year warranty is included with each model, and... Read more
Apple refurbished 2015 MacBook Airs available...
The Apple Store has Apple Certified Refurbished 2015 11″ and 13″ MacBook Airs (the latest models), available for up to $180 off the cost of new models. An Apple one-year warranty is included with... Read more
21-inch iMacs on sale for up to $120 off MSRP
B&H Photo has 21″ iMacs on sale for up to $120 off MSRP including free shipping plus NY sales tax only: - 21″ 1.4GHz iMac: $999.99 $100 off - 21″ 2.7GHz iMac: $1199.99 $100 off - 21″ 2.9GHz iMac... Read more
5K iMacs on sale for up to $150 off MSRP, fre...
B&H Photo has the 27″ 3.3GHz 5K iMac on sale for $1899.99 including free shipping plus NY tax only. Their price is $100 off MSRP. They have the 27″ 3.5GHz 5K iMac on sale for $2149.99 $2199.99, $... Read more

Jobs Board

*Apple* Desktop Analyst - KDS Staffing (Unit...
…field and consistent professional recruiting achievement. Job Description: Title: Apple Desktop AnalystPosition Type: Full-time PermanentLocation: White Plains, NYHot Read more
Simply Mac- *Apple* Specialist- Store Manag...
Simply Mac is the largest premier retailer for Apple products and solutions. We're looking for dedicated individuals with a passion to simplify and enhance the Read more
*Apple* Evangelist - JAMF Software (United S...
The Apple Evangelist is responsible for building and cultivating strategic relationships with Apple 's small and mid-market business development field teams. This Read more
*Apple* Retail - Multiple Positions (US) - A...
Sales Specialist - Retail Customer Service and Sales Transform Apple Store visitors into loyal Apple customers. When customers enter the store, you're also the Read more
*Apple* Desktop Analyst - KDS Staffing (Unit...
…field and consistent professional recruiting achievement. Job Description: Title: Apple Desktop AnalystPosition Type: Full-time PermanentLocation: White Plains, NYHot Read more
All contents are Copyright 1984-2011 by Xplain Corporation. All rights reserved. Theme designed by Icreon.