Learning that you can use unions in C for grouping things into namespaces

Anonymous nested structs are also quite useful for creating struct fields with explicit offsets:<p><pre><code> #include &lt;stdio.h&gt; #include &lt;stdint.h&gt; #define YDUMMY(suffix, size) char dummy##suffix[size] #define XDUMMY(suffix, size) YDUMMY(suffix, size) #define PAD(size) XDUMMY(__COUNTER__, size) struct ExplicitLayoutStruct { union { struct __attribute__((packed)) { PAD(3); uint32_t foo; }; struct __attribute__((packed)) { PAD(5); uint16_t bar; }; struct __attribute__((packed)) { PAD(13); uint64_t baz; }; }; }; int main(void) { &#x2F;&#x2F; offset foo = 3 &#x2F;&#x2F; offset bar = 5 &#x2F;&#x2F; offset baz = 13 printf(&quot;offset foo = %d\n&quot;, offsetof(struct ExplicitLayoutStruct, foo)); printf(&quot;offset bar = %d\n&quot;, offsetof(struct ExplicitLayoutStruct, bar)); printf(&quot;offset baz = %d\n&quot;, offsetof(struct ExplicitLayoutStruct, baz)); return 0; }</code></pre>

I&#x27;m using anonymous nested structs extensively for grouping related items, but I consider the extra field name a feature, not something that should be hidden:<p><a href="https:&#x2F;&#x2F;github.com&#x2F;floooh&#x2F;sokol-samples&#x2F;blob&#x2F;bfb30ea00b5948f2029c7dd228cf30de08b8036c&#x2F;sapp&#x2F;shdfeatures-sapp.c#L136-L165" rel="nofollow">https:&#x2F;&#x2F;github.com&#x2F;floooh&#x2F;sokol-samples&#x2F;blob&#x2F;bfb30ea00b5948f...</a><p>(also note the &#x27;inplace initialization&#x27; which follows the state struct definition using C99&#x27;s designated initialization)

The result is uglier and less maintainable than a pair of macros. Or just stop trying to hide syntax. This is ultimately on the same level as typedefing pointers.

The first example seems wrong, instead of `struct sub { ... };` what is meant is `struct { ... } sub;`

Doesn’t matter for C, but in C++ this could make your contexpr functions UB since you can only use one member of a union in constexpr contexts (the “active” member).

Imo this is not “perverse”. In my vector library I alias a vec3 as float x,y,z and float[3] using this technique.

The C programming language, brought to you by Cthulhu.<p>You don&#x27;t need eval(), you&#x27;ve got strcpy()!

I don&#x27;t regard this as a &quot;perverse&quot; hack. If I ever do embedded memory mapped stuff in C11 this is way too tempting.

Bleurgh. I have a deep soft spot for C, and I&#x27;m known to get twisted pleasure from using obscure language features in new ways to annoy people, but this is a level of abuse that even I can&#x27;t get behind. If you need namespacing, use C++. As much as I love C, it&#x27;s terrible for large projects.

This is probably a terrible idea, remember that if you have written one member of a union, all other members remain public, yet accessing any of them in any way is undefined behaviour. This is made way worse by most compilers mostly choosing to let you do what you think it will. They just dont guarantee they always will or in all cases.

Don&#x27;t actually do this.