Spirit Boost real_p parser behaving strangely - c++

Question

I have a following problem: I am reusing old code that uses real_p parser to parse real numbers. I would like to capture each number, convert it to string, and put it in vector of strings.
I am using the following code, where l_double is a variable of the type double, convertdouble function converts a double to a string, and result.m_literalValues is the vector of strings.
However, the code will not assign a parsed value to l_double.
rule<> alternative3 = +(real_p [assign_a(l_double)]
[push_back_a(result.m_LiteralValues, convertdouble(l_double))]
>> str_p(",")
)
Does anyone has an idea what am I doing wrong ?
Note: I will not re-engineer the old code, which is much more complex than the example given. I just want to extract the strings of all values parsed, and to put them in the vector of strings.

Answer 1

The problem seems to be located in push_back_a(result.m_LiteralValues, convertdouble(l_double)), specifically in convertdouble(l_double). push_back_a requires that its second argument be a reference to be stored in a "policy holder actor" so using the function call there causes the error. If you don't need to store l_double and were simply using it as a temporary, one way to accomplish what you want is creating your own phoenix function that behaves similarly to push_back_a as explained here(full example here).
You define the phoenix function like this:
struct push_back_impl
{
template <typename Container, typename Item>
struct result
{
typedef void type;
};
template <typename Container, typename Item>
void operator()(Container& c, Item const& item) const
{
c.push_back(convertdouble(item));
}
};
function<push_back_impl> const push_back = push_back_impl();
and then define your rule like this:
rule<> alternative3 = +( real_p[push_back(var(result.m_LiteralValues),arg1)] >> str_p(",") );
Full compilable code(change the for loop to show the results if you can't/don't want to use c++11):
#include <boost/spirit/include/classic_core.hpp>
#include <boost/spirit/include/classic_operators.hpp>
#include <boost/spirit/include/phoenix1_functions.hpp>
#include <boost/spirit/include/phoenix1_primitives.hpp>
#include <iostream>
#include <string>
#include <sstream>
#include <vector>
using namespace boost::spirit::classic;
using namespace phoenix;
std::string convertdouble(const double& d)
{
std::stringstream ss;
ss<<d;
return ss.str();
}
struct push_back_impl
{
template <typename Container, typename Item>
struct result
{
typedef void type;
};
template <typename Container, typename Item>
void operator()(Container& c, Item const& item) const
{
c.push_back(convertdouble(item));
}
};
function<push_back_impl> const push_back = push_back_impl();
struct Results
{
std::vector<std::string> m_LiteralValues;
};
int main()
{
Results result;
char const* test="2.5,3.6,4.8,";
rule<> alternative3 = +( real_p[push_back(var(result.m_LiteralValues),arg1)] >> str_p(",") );
if(parse(test,alternative3,space_p).full)
{
std::cout << "success" << std::endl;
for(auto& str :result.m_LiteralValues)
std::cout << str << std::endl;
}
else
{
std::cout << "failure" << std::endl;
}
return 0;
}