Objective-c main routine, what is: int argc, const char * argv[]

Question

What are the arguments passed into the main method of a command-line program:

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

what is the first int mean?

And what is the 2nd parameter, is that an array of chars?

How would one use these?

Also, what practical use is a command-line project type, other than using it to learn obj-c i.e. to practise.

Answer 1

argc means "argument count". It signifies how many arguments are being passed into the executable. argv means "argument values". It is a pointer to an array of characters. Or to think about it in another way, it is an array of C strings (since C strings are just arrays of characters).

So if you have a program "foo" and execute it like this:

foo -bar baz -theAnswer 42

Then in your main() function, argc will be 5, and argv will be:

argv[0] = "/full/path/to/foo";
argv[1] = "-bar";
argv[2] = "baz";
argv[3] = "-theAnswer";
argv[4] = "42";

Answer 2

The parameters to main() are a unix convention for accessing the arguments given on the command line when your program is executed. In a Cocoa app, you can access them the plain old C way, or you can use NSProcessInfo's -arguments method to get them in an NSArray of NSString objects, or use NSUserDefaults to get them as values in a dictionary.