Boost :: program_options for single byte variables
* highlighted text * How do I use Boost options to accept single-byte variables from the command line?
Command line parameters --id1=1 --id2=1
result in values โโid1 = 49 (or '1', 0x31) and id2 = 1.
#include <stdint.h>
#include <iostream>
#include <boost/program_options.hpp>
using namespace std;
int main(int argc, char** argv)
{
(void)argc;
(void)argv;
namespace po = boost::program_options;
const int myargc = 3;
const char* myargv[] = {"foo","--id1=1","--id2=2" };
uint8_t id1;
uint16_t id2; // works as expected.
po::variables_map vm;
po::options_description cmd_options( "Command options" );
cmd_options.add_options()
( "id1", po::value<uint8_t >( &id1 )->default_value( 0 ), "A 1-byte ID" )
( "id2", po::value<uint16_t>( &id2 )->default_value( 0 ), "A 2-byte ID" )
;
po::store( po::parse_command_line( myargc, myargv, cmd_options ), vm );
po::notify( vm );
// Using command line parameters of --id1=1 --id2=1,
// at this point, id1=49 (or '1', 0x31) and id2=1.
cout << "BPO parsing of " << myargv[1] << " and " << myargv[2] << endl;
cout << "id1: " << id1 << endl;
cout << "id1: " << (int)id1 << endl;
cout << "id2: " << id2 << endl;
id1 = boost::lexical_cast<uint8_t>("1");
id2 = boost::lexical_cast<int>("2");
cout << "Using boost::lexical_cast" << endl;
cout << "id1: " << id1 << endl;
cout << "id1: " << (int)id1 << endl;
cout << "id2: " << id2 << endl;
}
:
BPO parsing of --id1=1 and --id2=2
id1: 1
id1: 49
id2: 2
Using boost::lexical_cast
id1: 1
id1: 49
id2: 2
Boost ends up calling boost :: lexical_cast ("1") ', which is converted to a char, not a numeric value. The value "1" becomes "1", which is 49.
Is there a way to change the initialization of boost :: program_options :: add_options () to treat single-byte values โโas int rather than string / char? If not, what parameters do I need to change for parsing or matching? Obvious (but unfavorable) options are: [1] do not use char -like values โโ[2] manually parse (bypass Boost) or [3] do a secondary conversion after Boost parses it.
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Create a numeric byte class that represents the size of a byte, but stream as a numeric value, not stream as a char.
#include <stdint.h>
#include <iostream>
#include <boost/program_options.hpp>
using namespace std;
struct NumByte
{
uint8_t value;
NumByte() : value() {}
NumByte( const uint8_t &arg ) : value(arg) {}
NumByte( const NumByte &arg ) : value(arg.value) {}
operator uint8_t() const { return value; }
friend istream& operator>>(istream& in, NumByte& valArg)
{
int i;
in >> i;
valArg.value = static_cast<uint8_t>(i);
return in;
}
friend ostream& operator<<(ostream& out, NumByte& valArg)
{
out << static_cast<int>(valArg.value);
return out;
}
};
int main(int argc, char** argv)
{
(void)argc;
(void)argv;
namespace po = boost::program_options;
const int myargc = 3;
const char* myargv[] = {"foo","--id1=1","--id2=2" };
NumByte id1;
uint16_t id2;
po::variables_map vm;
po::options_description cmd_options( "Command options" );
cmd_options.add_options()
( "id1", po::value<NumByte >( &id1 )->default_value( 0 ), "A 1-byte ID" )
( "id2", po::value<uint16_t>( &id2 )->default_value( 0 ), "A 2-byte ID" )
;
po::store( po::parse_command_line( myargc, myargv, cmd_options ), vm );
po::notify( vm );
assert( sizeof(NumByte)==1 ); // insure the size of a numeric byte is the size of a byte.
cout << "BPO parsing of " << myargv[1] << " and " << myargv[2] << endl;
cout << "id1: " << id1 << endl;
cout << "id1: " << (int)id1 << endl;
cout << "id2: " << id2 << endl;
id1 = boost::lexical_cast<NumByte>("1");
id2 = boost::lexical_cast<int>("2");
cout << "Using boost::lexical_cast" << endl;
cout << "id1: " << id1 << endl;
cout << "id1: " << (int)id1 << endl;
cout << "id2: " << id2 << endl;
}
:
BPO parsing of --id1=1 and --id2=2
id1: 1
id1: 1
id2: 2
Using boost::lexical_cast
id1: 1
id1: 1
id2: 2
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The behavior you are observing is irrelevant to boost::program_options
or boost::lexical_cast
, it is just how stream extraction works for uint8_t
. The following demonstrates that
#include <iostream>
#include <sstream>
int
main()
{
uint8_t id1;
uint16_t id2;
std::istringstream iss( "1 1" );
iss >> id1 >> id2;
std::cout << "id1 char: " << id1 << std::endl;
std::cout << "id1 uint8_t: " << (uint8_t)id1 << std::endl;
std::cout << "id1 int: " << (int)id1 << std::endl;
std::cout << "id2 uint16_t: " << (uint16_t)id2 << std::endl;
std::cout << "id2 int: " << (int)id2 << std::endl;
}
gives:
id1 char: 1
id1 uint8_t: 1
id1 int: 49
id2 uint16_t: 1
id2 int: 1
If you want to limit your program parameters to one byte, I suggest using boost::numeric_cast
#include <stdint.h>
#include <iostream>
#include <boost/bind.hpp>
#include <boost/numeric/conversion/cast.hpp>
#include <boost/program_options.hpp>
int
main(int argc, char** argv)
{
(void)argc;
(void)argv;
namespace po = boost::program_options;
const int myargc = 3;
const char* myargv[] = {"foo","--id1=1","--id2=2" };
unsigned id1;
uint16_t id2; // works as expected.
po::options_description cmd_options( "Command options" );
cmd_options.add_options()
( "id1", po::value<unsigned>( &id1 )->notifier([](unsigned value){ boost::numeric_cast<uint8_t>(value); } ), "A 1-byte ID" )
( "id2", po::value<uint16_t>( &id2 ), "A 2-byte ID" )
;
po::variables_map vm;
po::store( po::parse_command_line( myargc, myargv, cmd_options ), vm );
po::notify( vm );
std::cout << "id1: " << id1 << std::endl;
std::cout << "id2: " << id2 << std::endl;
}
here is a sample session
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