How to handle exceptions when we give no argument to a C executable program [duplicate]

Question

I have this C program in which it should be given arguments like the following:

./program -i inputFile -o outputFile

and here's my related section of code

  while ((c = getopt(argc, argv, "i:o:")) != -1) {
            switch (c) {


                 case 'i':
                          inFile = strdup(optarg);
                 break;
                 case 'o':
                          outFile = strdup(optarg);
                 break;
                 default:

                          error_usage(argv[0]);

                      }
                }

also here's the error_usage function:

void error_usage(char *prog)
      {
        fprintf(stderr, "Usage: %s  -i inputfile -o outputfile\n", prog);
        exit(1);
      }

How should I modify my case statement in a way that if I run my program like the following: ./program it gives me the following error? Usage: prog -i inputfile -o outputfile

AndersK · Accepted Answer · 2013-09-23 05:09:20Z

2

Before you call getopt, check argc

if ( argc == 1 )
{
  fprintf(stderr, "... ");
  return -1;
}

answered Sep 23, 2013 at 5:09

AndersK

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15 Comments

john Over a year ago

And what if only one of the options was missing?

AndersK Over a year ago

you can check argc, if argc == 1 when there are no arguments, or argc == 2 if there is only one argument.

john Over a year ago

And what if the user repeated the -i argument? Then there would be the correct number of arguments, but the usage would still be wrong.

AndersK Over a year ago

then he would need to analyze the results after getopt, but that was not the question.

AndersK Over a year ago

@MonaJalal you would need to copy argv[0] into a buffer and then remove the path.

|

john · Accepted Answer · 2013-09-23 05:09:21Z

2

See inFile and outFile to NULL

Then after your getopts loop check to see if either is still NULL. If they are then print the usage message and exit

if (inFile == NULL || outFile == NULL)
    error_usage(argv[0]);

answered Sep 23, 2013 at 5:09

john

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2 Comments

P0W Over a year ago

Simply getopt can do the job

john Over a year ago

@P0W Then you should supply an answer

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