问题
I am writing a karma generator to generate a HTML page and I am experiencing inconsistent behavior while using column directive. It could very well be my understanding of how it works.
Basically I am generating a grid which requires me to insert some delimiters after every 2 occurrences of the data.
The below is a basic program I adopted to do a test run.
#include <boost/config/warning_disable.hpp>
#include <boost/spirit/include/karma.hpp>
#include <boost/fusion/include/struct.hpp>
#include <boost/fusion/include/nview.hpp>
#include <boost/assign/std/vector.hpp>
namespace fusion = boost::fusion;
namespace karma = boost::spirit::karma;
///////////////////////////////////////////////////////////////////////////////
namespace client
{
// Our employee struct
struct employee
{
int num;
std::string datatype;
std::string dataname;
std::string inputicon;
};
// define iterator type
typedef std::back_insert_iterator<std::string> iterator_type;
}
BOOST_FUSION_ADAPT_STRUCT(
client::employee,
(int, num)
(std::string, datatype)
(std::string, dataname)
(std::string, inputicon)
)
///////////////////////////////////////////////////////////////////////////////
int main()
{
std::string str;
// some employees
client::employee john = { 25, "int", "sra_command","fa fa-wrench" };
client::employee mary = { 25, "float", "swt_command","fa fa-wrench" };
client::employee tom = { 25, "double", "msc_command","fa fa-mobile" };
// now make a list of all employees and print them all
std::vector<client::employee> employees;
{
using namespace boost::assign;
employees += john, mary, tom;
}
{
typedef
fusion::result_of::as_nview<client::employee const, 1, 2, 3>::type
names_and_salary;
karma::rule<client::iterator_type, names_and_salary()> small_box =
"<startofblock>" << karma::string << "<after_first>"
<< karma::string << "<after_second>"
<< karma::string << "<after_third>";
std::string generated;
typedef std::back_insert_iterator<std::string> sink_type;
sink_type sink(generated);
karma::generate_delimited(sink, karma::columns(2,karma::string("nth_delimiter"))[small_box % karma::eol],karma::space,employees );
std::cout << generated << std::endl;
}
return 0;
}
The above generates the following output :
<startofblock>int<after_first>sra_command<after_second>fa fa-wrench<after_third>
nth_delimiter<startofblock>float<after_first>swt_command<after_second>fa fa-wrench<after_third>
nth_delimiter<startofblock>double<after_first>msc_command<after_second>fa fa-mobile<after_third> nth_delimiter
As noted , the nth delimiter occurs after every generation instead of every second.
The expected output is
<startofblock>int<after_first>sra_command<after_second>fa fa-wrench<after_third>
<startofblock>float<after_first>swt_command<after_second>fa fa-wrench<after_third>
nth_delimiter<startofblock>double<after_first>msc_command<after_second>fa fa-mobile<after_third>
回答1:
I think this comes close to what you want to achieve. Like I said, the last (incomplete) run will still be "terminated" with an nth_delimiter tag:
Live On Coliru
#include <boost/spirit/include/karma.hpp>
#include <boost/fusion/include/struct.hpp>
#include <boost/fusion/include/nview.hpp>
///////////////////////////////////////////////////////////////////////////////
namespace client {
struct employee
{
int num;
std::string datatype;
std::string dataname;
std::string inputicon;
};
typedef std::back_insert_iterator<std::string> iterator_type;
}
BOOST_FUSION_ADAPT_STRUCT(client::employee, /*num,*/ datatype, dataname, inputicon)
///////////////////////////////////////////////////////////////////////////////
int main() {
// some employees
std::vector<client::employee> const employees {
{ 25, "int", "sra_command","fa fa-wrench" },
{ 26, "float", "swt_command","fa fa-wrench" },
{ 27, "double", "msc_command","fa fa-mobile" },
{ 28, "int", "sra_command","fa fa-wrench" },
{ 29, "float", "swt_command","fa fa-wrench" },
{ 30, "double", "msc_command","fa fa-mobile" },
{ 31, "int", "sra_command","fa fa-wrench" },
{ 32, "float", "swt_command","fa fa-wrench" },
{ 33, "double", "msc_command","fa fa-mobile" },
};
// now print them all
std::string generated;
{
using namespace boost::spirit::karma;
using Sink = client::iterator_type;
//using Attr = boost::fusion::result_of::as_nview<client::employee const, 1, 2, 3>::type;
using Attr = client::employee;
rule<Sink, Attr()> small_box = "<B>" << string << "<1>" << string << "<2>" << string << "<3>";
generate(Sink(generated), columns(2, "<nth_delimiter>\n") [+small_box], employees);
}
std::cout << generated << std::endl;
}
Prints
<B>int<1>sra_command<2>fa fa-wrench<3><B>float<1>swt_command<2>fa fa-wrench<3><nth_delimiter>
<B>double<1>msc_command<2>fa fa-mobile<3><B>int<1>sra_command<2>fa fa-wrench<3><nth_delimiter>
<B>float<1>swt_command<2>fa fa-wrench<3><B>double<1>msc_command<2>fa fa-mobile<3><nth_delimiter>
<B>int<1>sra_command<2>fa fa-wrench<3><B>float<1>swt_command<2>fa fa-wrench<3><nth_delimiter>
<B>double<1>msc_command<2>fa fa-mobile<3><nth_delimiter>
Bonus:
The problem with smallbox % eol is that smallbox is an element, and eol too:
generate(Sink(generated), columns(4, "<nth_delimiter>") [small_box % eol], employees);
Live On Coliru
<B>int<1>sra_command<2>fa fa-wrench<3>
<B>float<1>swt_command<2>fa fa-wrench<3>
<nth_delimiter><B>double<1>msc_command<2>fa fa-mobile<3>
<B>int<1>sra_command<2>fa fa-wrench<3>
<nth_delimiter><B>float<1>swt_command<2>fa fa-wrench<3>
<B>double<1>msc_command<2>fa fa-mobile<3>
<nth_delimiter><B>int<1>sra_command<2>fa fa-wrench<3>
<B>float<1>swt_command<2>fa fa-wrench<3>
<nth_delimiter><B>double<1>msc_command<2>fa fa-mobile<3><nth_delimiter>
来源：https://stackoverflow.com/questions/43720071/inconsistent-generator-directive-column-behavior-in-boost-karma