boost fusion Quick Start

[georgebastille]

Hello all,

I hope this acceptable forum ettiquite, I have been learning how to use the boost fusion C++ library in preparation for an interview and wanted to post what has been frustrating me for a few hours now..

The Quick Start http://www.boost.org/doc/libs/1_52_0/li ... start.html runs through some examples of how to use the library. As a relative beginner not only to boost, but also to C++, I had some difficulty getting the examples to compile. Here is my minimum working example:

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#include <iostream>
#include <string>
#include <typeinfo>

#include <boost/fusion/container/vector.hpp> 
#include <boost/fusion/sequence.hpp>
#include <boost/fusion/algorithm/iteration/for_each.hpp>
#include <boost/fusion/algorithm/transformation/filter_if.hpp>
#include <boost/type_traits/is_pointer.hpp>
#include <boost/fusion/container/map.hpp>

using std::cout;
using std::endl;
using std::string;

// careful if also using std::vector
using boost::fusion::vector;
using boost::fusion::for_each;
using boost::fusion::filter_if;
using boost::fusion::at_c;
using boost::is_pointer;

// required for using the '_' placeholder
using mpl_::_;

// member functions for using the map
using boost::fusion::map;
using boost::fusion::pair;
using boost::fusion::at_key;
using boost::fusion::make_pair;

// prints the elements of a container as xml
struct print_xml
{
    template<class T>
    void operator()(T const& x) const
    {
        cout
            << '<' << typeid(x).name() << '>'
            << x
            << "</" << typeid(x).name() << '>'
            << endl;
    }
};

// finds the (normal) pointer elements of a Sequence and prints them as xml
template <typename Sequence>
void xml_print_pointers(Sequence const& seq)
{
    for_each(filter_if<is_pointer<_> >(seq), print_xml());
}

// define some types to show how the map associates types to values
namespace fields
{
    struct name;
    struct age;
}

int main()
{
    vector<int, char, string> stuff(1, 'x', "howdy");
    int i = at_c<0>(stuff);
    char ch = at_c<1>(stuff);
    string s = at_c<2>(stuff);
    
    cout << i << ", " << ch << ", " << s << endl;

    for_each(stuff, print_xml());
    
    int a = 1;
    int b = 2;
    int c = 3;
    int d = 4;
    
    vector<int, int*, int, int*> stuff2(a, &b, c, &d);
        
    xml_print_pointers(stuff2);
    
    cout << &b << endl << &d << endl;
    
    typedef map<pair<fields::name, string>,
	        pair<fields::age, int> > person;
		
    person a_person ( make_pair<fields::name>("Richie"),
		      make_pair<fields::age>(30));
		
    string person_name = at_key<fields::name>(a_person);
    int person_age = at_key<fields::age>(a_person);
    
    cout << person_name << " is " << person_age << endl;
    
    return 0;   
}

if it is saved in a file called fusion_example.cpp it can be compiled (with gcc) using the command:

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g++ -I/path/to/boost/libs -o fusion_example fusion_example.cpp

When run (./fusion_example) , it gives (on my computer):

1, x, howdy
<i>1</i>
<c>x</c>
<Ss>howdy</Ss>
<Pi>0x7fff41c4cf18</Pi>
<Pi>0x7fff41c4cf1c</Pi>
0x7fff41c4cf18
0x7fff41c4cf1c
Richie is 30

I hope this is helpful to anyone starting out with the very powerful boost library.

[neurodev]

First of all, I know its been a year but thank you for your post! The quick start guide has been frustrating to figure out.
I can only make minor improvements, for any other newbies searching for the same answer, you can minimize the headers required to the ones listed below.

Cheers georgebastille.

Code: Select all

#include <iostream>
#include <typeinfo>
#include <boost/fusion/include/vector.hpp>
#include <boost/fusion/algorithm.hpp>

#include <boost/type_traits/is_pointer.hpp>

using namespace boost::mpl::placeholders; //For the _