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

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?开发者_JAVA百科

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.

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";

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.

Just to add to the other answers - Objective-C targets both OS X and iOS. And while there is not much value in iOS command line applications, the shell on OS X is still widely used and there are lot of people writing command line tools.

That main is from C and not specific to objective-c. Argc gives you the number of command line arguments passed to your C program. Argv is an array of C strings and contains the command line arguments.

You would use them and the command-line project any time you wanted to write a command line tool or a program you interact with from the command line.

As wikipedia (and any other source says):

int main(void)

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

The parameters argc, argument count, and argv, argument vector, respectively give the number and value of the program's command-line arguments. The names of argc and argv may be any valid identifier in C, but it is common convention to use these names. In C++, the names are to be taken literally, and the "void" in the parameter list is to be omitted, if strict conformance is desired. Other platform-dependent formats are also allowed by the C and C++ standards, except that in C++ the return type must stay int; for example, Unix (though not POSIX.1) and Microsoft Windows have a third argument giving the program's environment, otherwise accessible through getenv in stdlib.h:

int main(int argc, char **argv, char **envp)

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

The practical use is creating a command-line tool using code from a Framework or Application that you have written. Helpers, utilities, launch agents and daemons, all of these background processes are typically implemented as command-line tools.