How can you iterate through and print the values of structure members in C using macros and Fusion libraries?

Iterating through Structure and Class Members

C provides ways for iterating through members of structs and classes to facilitate introspection and manipulation of their properties.

Using Macros

The REFLECTABLE macro defined in the accepted answer enables the definition of a struct that can expose its members for introspection. By adding REFLECTABLE before the member declarations, you can define a struct like:

<code class="cpp">struct A {
    REFLECTABLE
    (
        (int) a,
        (int) b,
        (int) c
    )
};</code>

To iterate and print the values of these members, you can use a custom visitor:

<code class="cpp">struct print_visitor {
    template<class FieldData>
    void operator()(FieldData f) {
        std::cout << f.name() << "=" << f.get() << std::endl;
    }
};

template<class T>
void print_fields(T & x) {
    visit_each(x, print_visitor());
}</code>

Using Fusion

Alternatively, you can adapt the struct to a fusion sequence using BOOST_FUSION_ADAPT_STRUCT:

<code class="cpp">struct A {
    int a;
    int b;
    int c;
};

BOOST_FUSION_ADAPT_STRUCT
(
    A,
    (int, a)
    (int, b)
    (int, c)
)</code>

To iterate and print the members, you can use a similar visitor function:

<code class="cpp">struct print_visitor {
    template<class Index, class C>
    void operator()(Index, C & c) {
        std::cout << boost::fusion::extension::struct_member_name<C, Index::value>::call() 
                  << "=" 
                  << boost:::fusion::at<Index>(c) 
                  << std::endl;
    }
};


template<class C>
void print_fields(C & c) {
    typedef boost::mpl::range_c<int,0, boost::fusion::result_of::size<C>::type::value> range;
    boost::mpl::for_each<range>(boost::bind<void>(print_visitor(), boost::ref(c), _1));
}</code>

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