how to limit the using of command line options in c using getopt()?

Question

I am working on a c project, which I am trying to write a program that allows users to use one of the command line options to invoke the program. For example

./program [-a or -b or -c] [-f filename] [-l length]

Which [-a or -b or -c] is compulsory, and -f and -l is not.

My question is, how to return an error if users choose any two or more of the [-a or -b or -c] at the same time?

This is allowed

./program -a -f -l

But not

./program -a -b -f -l

My thought is to use getopt() to verify the options, but I am not sure how to do this.

Thank you for your time! Sorry if I ask something stupid.

John Bode · Accepted Answer · 2022-10-16 15:33:24Z

1

All getopt does is make it easy to parse out command line options - it won't do any validation for you. You'll need to keep track of whether any of a, b, or c have been set:

bool abcSet = false;

while( (c = getopt( argc, argv, "abcf:l:" )) != -1 )
{
  switch( c )
  {
    case 'a':
      if ( !abcSet )
      {
        // processing for a
        abcSet = true;
      }
      else
        // error, b or c already set
      break;
 
    case 'b':
      // same as above
      break;

    case 'c':
      // same as above
      break;
    ...
  }

You can play around with the sense of the test or how you want to keep track of which option is set, but you have to keep track of that information somehow.

answered Oct 16, 2022 at 15:33

John Bode

125k19 gold badges130 silver badges211 bronze badges

Sign up to request clarification or add additional context in comments.

2 Comments

John Doe Over a year ago

Thank you, that's a very clear explanation

Jonathan Leffler Over a year ago

How do you tell which of the options -a, -b or -c was set? I would probably use char abc_flag = 0; and then in each option handler, have code like if (abc_flag && abc_flag != c) err_error(”cannot use both option -%c and -%c\n”, abc_flag, c); abc_flag = c; break;. That records which flag was set as well as whether it was set. After the option parsing loop, check that abc_flag is set. This allows the user to repeat a flag. If that's not wanted, simplify the check (but maybe complicate the error reporting). Since the code is the same for all three options, you can combine them.

dbush · Accepted Answer · 2022-10-16 14:49:49Z

0

getopt doesn't allow this degree of control.

There are two ways you can handle this:

Anytime you read one of these options, check to see if one of the others was already read.
After reading all options, check to see if more that one was given.

answered Oct 16, 2022 at 14:49

dbush

233k27 gold badges261 silver badges334 bronze badges

Collectives™ on Stack Overflow

how to limit the using of command line options in c using getopt()?

2 Answers 2

2 Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

2 Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related