Thread: Help with understanding arguments of int main()

This is really a noobish question I should already know the answer too since I've been programming for awhile, but what do the arguments in the main() function do? Such as:

Code:

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

I know "int argc" is the argument count, keeping track of all the arguments passed in the program from the command line. But even after reading some tutorials on this website and other articles online, I'm still lost to what its purpose is. Plus what exact "arguments" is it keeping track of and what does it do with them. Would some of these functions be considered an argument, argc would keep track of:

Code:

cout <<"Hello world!";

Or,

Code:

cin.get();

Or even,

Code:

return 1;

Also, what is "args"? I came across it while learning SDL. I know there is something called "argv" which I came across from the tutorial here on this website, which states "argv" as being the name of the program, or an empty string if the name is not known. What do both of these definitions mean?

And what is the purpose of the "char*" next to args? I thought it was making "char" read "args" as a pointer? Also, what is the [] meaning at the end of args, or seen in alot of other programs, "argv". I'm asking because I know you could change "char*" to "char**" and leave out the [] next to the second argument. So what is happening there?


Sorry for all these long-winded questions. I am just lost in all of this. In the past everytime I have had a question in programming, the community of cprogramming.com have ALWAYS been helpful so any comments will always be GREATLY appreciated!

NEVER MIND GUYS, I FOUND A PROGRAM! But I still need someone to tell me what the use of

Code:

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

does in this program I'm going to post below:

Code:

#include <SDL.h> 
int main( int argc, char* args[])
{
    SDL_Surface* message = NULL;
    SDL_Surface* screen = NULL;
    SDL_Init(SDL_INIT_EVERYTHING);
    screen = SDL_SetVideoMode(640, 480, 32, SDL_SWSURFACE);
    message = SDL_LoadBMP("hello.bmp");
    SDL_BlitSurface(message, NULL, screen, NULL);
    SDL_Flip(screen);
    SDL_Delay(2000);
    SDL_FreeSurface(message);
    SDL_Quit;
    return 0;
}

So basically what this program does is display a bmp.file. So is that why we add the two arguments in the int main function? Because it has to have that to use another file? If so, than now I definently understand it haha.

Originally Posted by cplusplusnoob

Can anyone give me an example of a program, such as a game or any other program with an actual use with

Code:

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

with a description of what the program does and give evidence for the use of

Code:

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

to of made it included in the program.

Thanks in advance!!

There are numerous examples. If a command line interface is documented for a program, then you could imagine the argv and argc parameters being used in some way (even if it's not written in C++, just think of it if you were porting the program to C++).

Internet Explorer Command-Line Options

Other examples include:
Foobar2000:Commandline Guide - Hydrogenaudio Knowledgebase
7-Zip
Winamp Application Programming Interface - Winamp Forums

Pretty much any program can be invoked if you know its name, and programs that have a GUI may not be as well documented as things that do not have one.

No, that program makes no use of the arguments passed; therefore it's a poor example. It could just as well have been written with int main(void).

Nearly any command line program will use command line arguments, like pretty much every tool in the UNIX/Linux toolset.

Originally Posted by Neo1

If you run your program from the console like this: "main.exe", then argv[0] will just be "main.exe" and argc will be zero.

incorrect. argc will be 1 in this case.

Originally Posted by rags_to_riches

No, that program makes no use of the arguments passed; therefore it's a poor example.

Which program are you talking about? The one I put up? It MUST use

Code:

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

because I tried using just

Code:

 int main()

and

Code:

 int main(void)

just to see if anything different would happen and the programmed stop working afterwards until I put back the arguments in the main function.... So it has to use it somewhere in the program??

When you say it stopped working, what do you mean? If you got compiler errors related to argc or args, then you certainly do need the parameter list version of main regardless of what we see. To us it looks like the parameters aren't being used at all.

Originally Posted by whiteflags

When you say it stopped working, what do you mean? If you got compiler errors related to argc or args, then you certainly do need the parameter list version of main regardless of what we see. To us it looks like the parameters aren't being used at all.

Well, the compilier recieves an error, but it doesn't highlight the error, as if you had forgotten a semi-colon. It say's in blue text that the statement is a reference and not a call, to functoin "SDL_Quit". And if I delete "SDL_Quit"(I just did that to experiment, the program needs SDL_Quit to clean up), and still use just int main() or int main(void), it says "undefined reference to SDL_main...

So this is what confuses me and paremeters?

Try calling SDL_Quit correctly like in this example (SDL_Quit - SDL Documentation Wiki) and it will fix the error.

This has nothing to do with command line arguments after all.