问题
I am having a problem with boost program_options (v1_49) in the case of an option defined as composing() and also implicit(). My intent is to implement a -D option similar to the way perl does, so that you can do -D or -Dname and use it multiple times. My options_description is:
( "debug,D",
bpo::value<vector<string> >()
->composing()
->implicit_value(vector<string>(1,"1")),
"Set debug level."
),
This seems to work OK in most cases, but whenever -D with no value appears on the command line, all earlier values are erased, e.g.:
$ ./a.out -D abc -D 255 -D xyz
variables_map["debug"] = {"abc", "255", "xyz"}
$ ./a.out -D -D 255 -D xyz
variables_map["debug"] = {"1", "255", "xyz"}
$ ./a.out -D abc -D -D xyz
variables_map["debug"] = {"1", "xyz"}
$ ./a.out -D abc -D 255 -D
variables_map["debug"] = {"1"}
I think I see why this happens, the implicit value {"1"} replaces the existing vector instead of adding to it. Is there something I can do to get this to work or is it a limitation of boost::program_options?
回答1:
Here's a workaround that doesn't require modifying boost sources. If you separate the parse and store tasks then you can modify the intermediate boost::program_options::parsed_options vector of options. Each element of the vector contains the std::string key and a std::vector<std::string> of values. The workaround relies on the fact that for implicit values, that vector of values is empty. If we scan parsed_options for implicit values and explicitly assign them a value then they don't clobber previous values of the same key. Here's working code:
#include <iostream>
#include <string>
#include <vector>
#include <boost/foreach.hpp>
#include <boost/program_options.hpp>
namespace po = boost::program_options;
namespace std {
// This overload is needed to use composed options.
static std::ostream& operator<<(
std::ostream& os,
const std::vector<std::string>& v) {
os << '{';
BOOST_FOREACH(const std::string& s, v) {
if (&s != &*v.begin())
os << ", ";
os << '"' << s << '"';
}
os << '}';
return os;
}
}
int main(int argc, char *argv[]) {
po::options_description desc("Allowed options");
desc.add_options()
("debug,D",
po::value<std::vector<std::string> >()
->composing()
->implicit_value(std::vector<std::string>(1,"1")),
"Set debug level.");
// Just parse the options without storing them in the map.
po::parsed_options parsed_options = po::command_line_parser(argc, argv)
.options(desc)
.run();
// Implicit option values are empty, replace with default value.
BOOST_FOREACH(po::option& o, parsed_options.options) {
if (o.string_key == "debug" && o.value.empty())
o.value.push_back("1"); // default value is "1"
}
// Now store and earlier values aren't clobbered.
po::variables_map vm;
po::store(parsed_options, vm);
po::notify(vm);
std::cout << "variables_map[\"debug\"] = "
<< (vm.count("debug") ?
vm["debug"].as<std::vector<std::string> >() :
std::vector<std::string>())
<< '\n';
return 0;
}
And here's those same test cases:
$ ./a.out -D abc -D 255 -D xyz
variables_map["debug"] = {"abc", "255", "xyz"}
$ ./a.out -D -D 255 -D xyz
variables_map["debug"] = {"1", "255", "xyz"}
$ ./a.out -D abc -D -D xyz
variables_map["debug"] = {"abc", "1", "xyz"}
$ ./a.out -D abc -D 255 -D
variables_map["debug"] = {"abc", "255", "1"}
回答2:
Well, I eventually figured out a solution that seems to work for me. It would be nice to have some independent verification from somebody fluent in boost::program_options if possible, but apparently nobody seems to know or care much about it.
Here is a patch to boost_1_49_0 that will allow an option to be both composing() and also have an implicit_value().
diff -Naur old/boost/program_options/detail/value_semantic.hpp new/boost/program_options/detail/value_semantic.hpp
--- old/boost/program_options/detail/value_semantic.hpp 2010-07-12 03:14:14.000000000 -0400
+++ new/boost/program_options/detail/value_semantic.hpp 2012-08-17 16:31:03.000000000 -0400
@@ -154,6 +154,28 @@
}
}
+ // Helper function to copy a non-vector implicit value into the
+ // tokens vector.
+ template<class T, class charT>
+ void get_implicit_tokens(std::vector<std::basic_string<charT> >& vs,
+ const boost::any& a,
+ T*, long) {
+ const T va = boost::any_cast<const T>(a);
+ vs.push_back(boost::lexical_cast<std::basic_string<charT> >(va));
+ }
+
+ // Helper function to copy a vector implicit value into the
+ // tokens vector.
+ template<class T, class charT>
+ void get_implicit_tokens(std::vector<std::basic_string<charT> >& vs,
+ const boost::any& a,
+ std::vector<T>*, int) {
+ const std::vector<T> va = boost::any_cast<const std::vector<T> >(a);
+ for (unsigned i = 0; i < va.size(); i++) {
+ vs.push_back(boost::lexical_cast<std::basic_string<charT> >(va[i]));
+ }
+ }
+
template<class T, class charT>
void
typed_value<T, charT>::
@@ -164,7 +186,14 @@
// value, then assign the implicit value as the stored value;
// otherwise, validate the user-provided token(s).
if (new_tokens.empty() && !m_implicit_value.empty())
- value_store = m_implicit_value;
+ if (m_composing) {
+ // Attempt to append the implicit value.
+ std::vector<std::basic_string<charT> > vs;
+ get_implicit_tokens(vs, m_implicit_value, (T*)0, 0);
+ validate(value_store, vs, (T*)0, 0);
+ } else {
+ value_store = m_implicit_value;
+ }
else
validate(value_store, new_tokens, (T*)0, 0);
}
来源：https://stackoverflow.com/questions/11778153/boost-program-options-with-composing-and-implicit-value-are-not-composed