*强调文本*如何使用Boost程序选项从命令行接受单字节变量?
--id1=1 --id2=1
的命令行参数导致id1 = 49(或'1',0x31)和id2 = 1的值。
#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;
}
输出是:
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最终调用boost :: lexical_cast(“1”)',它转换为char而不是数值 - “1”变为'1',即49.
有没有办法更改boost :: program_options :: add_options()初始化,将单个值视为int而不是string / char?如果没有,我有什么选择来改变解析或映射?明显(但不利)的选项是:[1]不要使用类似char的值[2]手动解析(绕过Boost)或[3]在Boost解析后执行二次转换。
答案 0 :(得分:3)
您观察到的行为与boost::program_options
或boost::lexical_cast
无关,而是uint8_t
类型的流提取工作原理。
#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;
}
产生
id1 char: 1
id1 uint8_t: 1
id1 int: 49
id2 uint16_t: 1
id2 int: 1
如果您想将程序选项限制为单个字节,建议您使用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;
}
这是一个sample session
答案 1 :(得分:2)
创建一个字节大小的数字字节类,但是像数字值一样流,而不是像char一样流式传输。
#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;
}
输出是:
BPO parsing of --id1=1 and --id2=2
id1: 1
id1: 1
id2: 2
Using boost::lexical_cast
id1: 1
id1: 1
id2: 2