<blockquote>
<p>Does it realistically ever not crash though?</p>
</blockquote>
<p>It depends on the system, optimization level, what <code>NULL</code> actually is, and so on. For example, when the optimizer sees <code>doc->file_name</code> without any check that it's not <code>NULL</code> guarding it, it is free to re-write/optimize that code any way it sees fit, as long as the result is the same. It's possible that what it produces will do something different than segfault if <code>doc</code> ends up actually being <code>NULL</code>.</p>
<p>As to how likely/realistic it is, I cannot say, but it's never good to rely on undefined behaviour.</p>

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