Cocoa: int main function

Question

I'm curious, what role does the int main function play in a Cocoa program? Virtually all of the sample code I've been looking at has only the following code in main.m:

#import <Cocoa/Cocoa.h>


int main(int argc, char *argv[])
{

    return NSApplicationMain(argc,  (const char **) argv);
}

What exactly is this doing, and where does the program actually start stepping through commands? It seems my conceptions need readjustment.

Answer 1

Since a Cocoa project starts like any other, the entry point for the Operating system is main. However the Cocoa Architecture is constructed to actually start the processing of your program from NSApplicationMain, which is responsible for loading the initial window from your application and starting up the Events loop used to process GUI events.

Apple has a very in depth discussion on this under the Cocoa Fundamentals Guide : The Core Application Architecture on Mac OS X

Answer 2

If you want to learn how control passes from "launch this" to the main() function, the execve man page has the details. You would also want to read about dyld. main() is a part of the Unix standard. Every single program that you can run effectively has a main().

As others have mentioned, NSApplicationMain passes control to Cocoa. The documentation is quite specific as to what it does.

One interesting note, NSApplicationMain doesn't actually every return. That is, if you were to separate the call to NSApplicationMain from the return in your main function and put code in between, that code would never be executed.