__vic/doc/en/packon.h.xml

<chapter xml:id="packon.h">
<title><tt>__vic/packon.h</tt> &amp; <tt>__vic/packoff.h</tt></title>

<p>Inclusion of the first file turns off struct members alignment. In other
words, turns on "structures packing" - size of the struct is strictly a sum of
its members sizes. Inclusion of the second one restores the default alignment.
So that the pair of <tt>#include</tt> directives forms a section in the source
file where structs alignment is disabled.</p>

<note>Each <tt>#include&lt;__vic/packon.h></tt> must have the corresponding
<tt>#include&lt;__vic/packoff.h></tt>.</note>

<section><title>Example</title>
<code-block lang="C++"><![CDATA[
struct unpacked
{
    bool f1;
    int f2;
};
static_assert(sizeof(unpacked) >= sizeof(bool) + sizeof(int),
    "Total struct size can exceed the sum of members sizes");

#include<__vic/packon.h> // alignment disabled starting from here

struct packed
{
    bool f1;
    int f2;
};
static_assert(sizeof(packed) == sizeof(bool) + sizeof(int),
    "Total struct size is exactly the sum of members sizes");

#include<__vic/packoff.h> // alignment enabled again
]]></code-block>
</section>

</chapter>