I am working on an application that reads some options through a config file. The code uses boost program_options library to read the options.
The application code has a class that does the following tasks related to reading the option values-
1)function1() - defines all the possible options that are valid. Adds them to an option_description object.
2)function2() - parses the config file and populates the variable_map object.
3)function3() - returns the value of an option.This function looks like this -
template<typename T>
T function3(string optName){
try{return vm[optName].as<T>();}
catch(exception& e){ //some error handling message}
}
Now for an option like-
vector_of_string_option=value1,value2,value3
For this I add this option to the options description object as-
("vector_of_string_option", po::value<vector<string>>(), "vector string");
For this vm["vector_of_string_option"].as<vector<string>>() returns a vector with first element - "value1,value2,value3"
I want the returned value to be a vector containing 3 values - {"value1" , "value2" , "value3"}.
Since function3() is a templatized function in the class, I cannot write a specialized function for vector(that would split the string say, using boost::split).
If there is a way I will use the same for vector.
So, is there a way to achieve this inherently through program_options? or any other suggestion to achieve this in my code?
The idea for you using Boost Program Options is to use multi-token/composing options.
Let's follow along
1)
function1()- defines all the possible options that are valid. Adds them to anoption_descriptionobject.
auto function1() {
po::options_description desc;
for (auto opt : s_opts)
desc.add_options()(opt, po::value<std::string>());
desc.add_options()
("vector_of_string_option", po::value<VoS>()->multitoken()->composing(), "vector string")
;
return desc;
}
So far so good
2)
function2()- parses the config file and populates thevariable_mapobject.
auto function2(std::istream&& is) {
auto d = function1();
po::parsed_options parsed = po::parse_config_file(is, d, false);
po::variables_map vm;
po::store(parsed, vm);
po::notify(vm);
return vm;
}
Still no problems.
3)function3() -
returns the value of an option.This function looks like this -
template <typename T>
T function3(std::string optName, po::variables_map const& vm) {
try {
return vm[optName].as<T>();
} catch (std::exception const& e) {
std::cerr << "Whoops: " << e.what() << "\n";
exit(1);
}
}
Ok.
int main() {
auto vm = function2(std::istringstream(R"(
bar=BARRRR
# bar=QUXXXX # "cannot be specified more than once"
vector_of_string_option=value1
vector_of_string_option=value2
vector_of_string_option=value3
)"));
std::cout << function3<std::string>("bar", vm) << "\n";
for (auto& v : function3<VoS>("vector_of_string_option", vm)) {
std::cout << " - " << std::quoted(v) << "\n";
}
}
Prints:
BARRRR
- "value1"
- "value2"
- "value3"
I want the returned value to be a vector containing 3 values - {"value1" , "value2" , "value3"}.
Already done, see it Live On Coliru
Since function3() is a templatized function in the class, I cannot write a specialized function for vector(that would split the string say, using boost::split).
Sure you can! You cannot /partially/ specialize, but you can specialize:
template <>
VoS function3<VoS>(std::string optName, po::variables_map const& vm) {
try {
VoS result;
auto const& raw = vm[optName].as<VoS>();
using namespace boost::algorithm;
for(auto& rv : raw) {
VoS tmp;
split(tmp, rv, is_any_of(",; "), token_compress_on);
result.insert(result.end(), tmp.begin(), tmp.end());
}
return result;
} catch (std::exception const& e) {
std::cerr << "Whoops: " << e.what() << "\n";
exit(1);
}
}
That makes it so you can multiple values, but also split each:
int main() {
auto vm = function2(std::istringstream(R"(
bar=BARRRR
# bar=QUXXXX # "cannot be specified more than once"
vector_of_string_option=value1, value2, value3
vector_of_string_option=value4, value5, value6
)"));
std::cout << function3<std::string>("bar", vm) << "\n";
for (auto& v : function3<VoS>("vector_of_string_option", vm)) {
std::cout << " - " << std::quoted(v) << "\n";
}
}
Prints
BARRRR
- "value1"
- "value2"
- "value3"
- "value4"
- "value5"
- "value6"
Again, see it Live On Coliru
If you wanted partial specialization, either delegate implemention of function3 to a template class, or use tag dispatch. That would make it possible/easy to parse into set<int> or list<bool> as well.