From: Marcin Kalicinski (kalita_at_[hidden])
Date: 2006-04-20 14:53:35
Hi Everybody,
I see there is some confusion about possible overlap of program_options
library and property_tree libraries. I will try to present my view on the
problem here.
First of all, my opinion is there is very little overlap. The biggest
difference between the libraries is that property_tree is hierarchical and
program_options is linear - i.e. options are accessible through a map-like
interface.
Structure of file formats, like XML, JSON etc. is inherently hierarchical.
The presence of hierarchy is their greatest strength, and most important
feature. Large amount of information is conveyed by structure of the tree
alone, not only by values of options it contains. One option in two
different branches of the tree can have completely different meaning.
Contrary to that, in program_options library there is only at best a notion
of "positional options" which is completely different from hierarchy.
Briefly, PO library operates on a flat strings of options, property_tree is
a DOM. Think of property_tree like a replacement for Microsoft XML parser,
or JSON API, or Windows INI API, or registry API. Do you imagine using
program_options to XML trees, like you get from XML parser? It is not suited
for that, its problem domain lies in completely different place, namely
parsing a linear string of (command-line) options, possibly supplied as a
config file or files.
In addition to that, PO library does not support writing the structures back
to config files. It is not a flaw with the library, it just does not need to
do it, because options for programs are meant to be "one shot", or "read and
forget", like command line arguments. There's not need to store them back
where they came from.
On the other hand, PO library supports many things that do not belong to
property_tree. These include, for example, options descriptions and notify()
mechanisms.
Taking all that into account I do not see why anybody insists there might
exist 1:1 correspondence between the libraries. I agree both can parse
command lines, but that's about it. Other functionality is very different.
Best regards,
Marcin