Question on proper use of QCommandLineOption?

[jefftee]

Sure, a typical usage would be:

tablesync -i -c test.csv -t incident_data ~/db/sqlite.db

tablesync -i -c test.csv -t incident_data ~/db/sqlite.db

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Here's also the "tablesync -h" output that is automatically built:

mbp02:~/develop/tablesync[develop]$ tablesync -h
Usage: tablesync [options] db
 
Options:
  -h, --help               Displays this help.
  -v, --version            Displays version information.
  -c, --csvfile <csvfile>  The CSV file with desired fields.
  -i, --import             Import the CSV file into tablename
  -s, --sync               Sync tablename with the CSV file fields.
  -t, --table <tablename>  The target table name.
 
Arguments:
  db                       The database file to process.

mbp02:~/develop/tablesync[develop]$ tablesync -h
Usage: tablesync [options] db

Options:
  -h, --help               Displays this help.
  -v, --version            Displays version information.
  -c, --csvfile <csvfile>  The CSV file with desired fields.
  -i, --import             Import the CSV file into tablename
  -s, --sync               Sync tablename with the CSV file fields.
  -t, --table <tablename>  The target table name.

Arguments:
  db                       The database file to process.

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As shown above, the only positional argument is the last, so that requires that all cmd line options that start with a "-" must precede any positional arguments. The Qt behavior with QCommandLineParser seems pretty sane/normal to me, so I'm quite happy to use it rather than have to deal with the differences between getopt(s) on different OS platforms, etc.

[TorAn]

Thanks! What is still unclear to me is the case where there are more then one "positionalArgument". In your case it is "db" and you expect only one argument there. But what if there are more then one positionalArguments? Like, "db" and "openReadOnly" or something similar? How to distinguish between two or more positionalArguments?

[jefftee]

See line 16 in the code I posted. Positional args are stored in a QStringList named args, so args.size() will tell you how many positional args were present, and args[0] is the first, args[1] is the 2nd, etc. You can have as many positional args as you want, but they must follow any other options that start with "-" or "--" and you can't have a missing (default) positional argument unless it's the last one (and perhaps only).

Hope that helps.

[TorAn]

Right, I understood that from the code you posted. Let's say your command line has two positional args, "db1" and "db2" with values ~/db/sqlite1.db and ~/dbsqlite2.db. So, the command line will look like this, right?

tablesync -i -c test.csv -t incident_data ~/db/sqlite1.db ~/dbsqlite2.db.

How do you know which one is db1 and which one is db2?

[jefftee]

Yes, for the example you posted above, db1 would be ~/db/sqlite1.db and db2 would be ~/db/sqlite2.db. You would define the two positional arguments like so:

parser.addPositionalArgument("db1", "The source database file to process."); // first positional argument
parser.addPositionalArgument("db2", "The destination database file to process."); // second positional argument

parser.addPositionalArgument("db1", "The source database file to process."); // first positional argument
parser.addPositionalArgument("db2", "The destination database file to process."); // second positional argument

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Remember, positional args are just that, their usage is based solely in the order in which they appear, not based on their values or naming, etc.

In the example above, where you had two positional arguments: ~/db/sqlite1.db ~/dbsqlite2.db, if you screwed up and entered them in reverse order: ~/db/sqlite2.db ~/db/sqlite1.db, then your program will use ~/db/sqlite2.db as db1 and ~/db/sqlite1.db as db2. Think of it like the DOS copy command or Unix cp command where both take a source and target positional argument, i.e. cp source.txt target.txt, which would copy the source.txt file to a new file called target.txt, etc.

[TorAn]

Thank you so much for your help and patience. I could not believe my eyes and your explanations up until the very end. I still find it strange that the designer(s) of positional arguments would use argument order to determine the input value, even though the argument names are available. I kind of ignored the name "PositionalArgument", shame on me.
Thanks again.

[anda_skoa]

Thank you so much for your help and patience. I could not believe my eyes and your explanations up until the very end. I still find it strange that the designer(s) of positional arguments would use argument order to determine the input value, even though the argument names are available.

Positional means that the argument is identified by its position.
I.e. you can't have the second without having the first.

Btw, your original problem sounded more like passing a value to a specific commandline switch, i.e. from your description I would have assumed you have a "p" option that has a parameter that can either be "ttt" or "mmmm".

Cheers,
_

[TorAn]

Turned out I cannot even use these classes. As I discovered (3 days too late. Clearly spelled out in the documentation, though):

when an error happens (for instance an unknown option was passed), the current process will then stop, using the exit() function.

What a strange design...Hopefully this thread will be a warning to others who want to try using these two classes for something other then parsing command-line arguments.

[jefftee]

If you want control over error handling for invalid options, use QCommandLineParser::parse() instead of QCommandLineParser::process().