Variable Arguments through Command Line

zombiezparadize · 05-06-2008, 06:02 AM

I was called for a Code review and I saw some code as below:

Code:

if(argc!=1)

Whoa!

Quote:

I raised a comment saying, the code doesn't restrict the user from entering any number of arguments he/she wants to and if disguised well, this could account for a buffer overflow!

To this I got the response from the programmer saying:

Quote:

Good Comment but the problem here is that the number of arguments that the program is accepting is variable and so I am finding it hard to implement.

Now my question is, what would be the better way to go?
Implementing a limit on the number of parameters that the user can send (there certainly has to be one as the code cant keep processing all possible values of argv[], I know argv[] is not of constant size anyway.)

I have never seen va_args being used to work on arguments passed from the command line.

zacs7 · 05-06-2008, 06:05 AM

argc = Argument count (the amount of arguments in the argv)
argv = Argument Vector (holds arguments)

I don't get your question, you want to stay in bounds? That's easy -- just keep within 0 to argc - 1

If you want to check if element n exists,

Code:

if(n < argc)
    n exists!

zombiezparadize · 05-06-2008, 06:58 AM

On going through the post again, yeah I agree it is asking a pretty vague or rather a question that is too obvious.
I was more concerned about the the comparison.
If the programmer were to write what he wrote

Code:

if(argc!=1)

then he should have also defined what should happen if argc=1.

Sorry about the vague post. Too many things in mind cause such blunders.

matsp · 05-06-2008, 07:14 AM

Actually, if(argc != 1) is "is there any arguments". argc should never be able to be negative, and 0 is invalid, as argv[0] is the name of the program (or something along those lines).

However, there should probably be some "else" or similar to that if-statement - but I guess it is valid to just "do nothing" (or "do some default") if there are no arguments.

As long as argument access is within the bounds of 0 ... (argc-1), then it's valid.

--
Mats

**laserlight** · 05-06-2008, 07:22 AM

Quote:

and 0 is invalid, as argv[0] is the name of the program (or something along those lines).

0 is technically valid, in which case argv[0] is a null pointer, and that's about all that's defined for the case argc=0.

zombiezparadize · 05-06-2008, 07:35 AM

Quote:

Originally Posted by matsp

However, there should probably be some "else" or similar to that if-statement - but I
guess it is valid to just "do nothing" (or "do some default") if there are no arguments.

--
Mats

The "do some default" or "do nothing" was exactly what was missing from the code!
Which means when there are no arguments passed to the program the code will merrily
throw SIGSEGV as it is going to access

Code:

 *++argv  /* As used by the programmer though I hate writing such operator precedence 
dependent code. I find it very unreadable*/

Anyway, thank you all for the inputs!
@laserlight: argc=0 . I didn't know that one. Thanks!

05-06-2008, 06:05 AM	#2
zacs7 Woof, woof! Join Date: Mar 2007 Location: Australia Posts: 3,139	argc = Argument count (the amount of arguments in the argv) argv = Argument Vector (holds arguments) I don't get your question, you want to stay in bounds? That's easy -- just keep within 0 to argc - 1 If you want to check if element n exists, Code: if(n < argc) n exists! __________________ "I.T. gets the chicky-babes" - M. Kelly bakefile \| vim Last edited by zacs7; 05-06-2008 at 06:18 AM.
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05-06-2008, 06:58 AM	#3
zombiezparadize Day Dreamer Join Date: Apr 2007 Posts: 45	On going through the post again, yeah I agree it is asking a pretty vague or rather a question that is too obvious. I was more concerned about the the comparison. If the programmer were to write what he wrote Code: if(argc!=1) then he should have also defined what should happen if argc=1. Sorry about the vague post. Too many things in mind cause such blunders. __________________ I would love to change the world but they dont give me the source code!
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05-06-2008, 07:14 AM	#4
matsp Kernel hacker Join Date: Jul 2007 Location: Farncombe, Surrey, England Posts: 15,686	Actually, if(argc != 1) is "is there any arguments". argc should never be able to be negative, and 0 is invalid, as argv[0] is the name of the program (or something along those lines). However, there should probably be some "else" or similar to that if-statement - but I guess it is valid to just "do nothing" (or "do some default") if there are no arguments. As long as argument access is within the bounds of 0 ... (argc-1), then it's valid. -- Mats __________________ Compilers can produce warnings - make the compiler programmers happy: Use them! Please don't PM me for help - and no, I don't do help over instant messengers.
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