Re: [boost] [program_options] allowing unknown options (from third party libraries)

From: Christophe Prud'homme (prudhomm_at_[hidden])
Date: 2005-10-27 05:15:14

Hi Vladimir,

[ Jeudi 27 Octobre 2005 11:30 ]
| Hi Christophe,
|
| > I could not find in the doc whether it is possible to have unknown
| > options in the command line and tell the parsers to not worry about them.
| > If it is already a feature, then perhaps it should be documented.
| > Otherwise I think it could be a nice addition.
| > the rationale is that there are framework/libraries out there with there
| > own command line options : for example MPI and PETSC
|
| Hmm.. it looks like there's some bad fate with this feature. It was already
| present in 1.32, but it was hidden deep inside private interfaces, and so
| not usable. For 1.33, I did some refactoring to fix this but looking again,
| it looks like it's still not usable, because I privately derive from the
| class implementing the relevant method :-(
|
| I've now fixes that, added a test, and even a documentation. It's in CVS
| HEAD, and I'll merge it to 1.33.1 branch soon.
super !

| Here's the extract from the documentation:
|
| 	Allowing unknown options
|
|
|     Usually, the library throws an exception on unknown option names. 
Yeah what I do now is catch the exception to be able to pass options to 
MPI(message passing interface)

|     This 
|     behaviour can be changed. For example, only some part of your
| application uses Program_options, and you wish to pass unrecognized options
| to another part of your program, or even another application.
Yup exactly (third party libraries also: mpi, petsc,...)

|     To allows unregistered options on the command line, you need to use the
|     basic_command_line_parser class for parsing (not parse_command_line)
| and call the allow_unregistered method of that class:
|
|     parsed_options parsed =
|         command_line_parser(argv, argc).options(desc).
| 		allow_unregistered().run();
Good that it is not the default behaviour !

|     For each token that looks like an option, but does not have a known
| name, an instance of basic_option will be added to the result. The
| string_key and value fields of the instance will contain results of
| syntactic parsing of the token, the unregistered field will be set to true,
| and the original_tokens field will contain the token as it appeared on the
| command line.
|
|
|      If you want to pass the unrecognized options further, the
|      collect_unrecognized function can be used. The function will collect
|      original tokens for all unrecognized values, and optionally, all found
|      positional options. Say, if your code handles a few options, but does
| not handles positional options at all, you can use the function like this:
|
|      vector<string> to_pass_further = collect_arguments(parsed.option,
|      include_positional);
I think that's very convenient. A lot of libraries which get initialized with 
command line options take the usual (int argc, char** argv)

for example., if I understand correctly,  with your changes we have
int main(int argc,char** argv)
{
 // do the usual program_options stuff
 // get further(unregistered) options to pass
 unreg_argc= to_pass_further.size();
 char** unreg_argv = transform_to_charstarstar( to_pass_further );

 MPI_Init(unreg_argc,unreg_argv);
 PETSCInitialize(unreg_argc,unreg_argv);
}

Thank you for this very convenient addition, that adds good flexibility to 
program_options in the presence of alien systems :)

Best regards
C.
-- 
MIT Affiliate
Debian/GNU/Linux developer for scientific computing packages
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