Can You Dynamically Traverse Struct and Class Members in C ?

Iterative Exploration of Struct and Class Members

In C , is it feasible to traverse a struct or class and discover all its members? Consider the following examples:

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

class b
{
  public:
    int a;
    int b;
  private:
    int c;
};</code>

Is it possible to iterate through these structures and print statements such as "Struct a has int named a, b, c" or "Class b has int named a, b, c"?

Solution

To achieve this, you can utilize macros or adapt the struct as a fusion sequence.

Method 1: REFLECTABLE Macro

Define the struct using the REFLECTABLE macro as seen below:

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

Subsequently, iterate over the fields and print each value:

<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 &amp; x)
{
    visit_each(x, print_visitor());
}

A x;
print_fields(x);</code>

Method 2: Fusion Sequence Adaptation

Adapt the struct as a fusion sequence:

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

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

Print the fields using this approach:

<code class="cpp">struct print_visitor
{
    template<class Index, class C>
    void operator()(Index, C &amp; 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 &amp; 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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