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<h1 class="main">Memory-unsafe code</h1>
<p>Sometimes for efficiency you may want to write low-level code that can potentially
corrupt memory or be vulnerable to security exploits. V supports writing such code,
but not by default.</p>
<p>V requires that any potentially memory-unsafe operations are marked intentionally.
Marking them also indicates to anyone reading the code that there could be
memory-safety violations if there was a mistake.</p>
<p>Examples of potentially memory-unsafe operations are:</p>
<ul>
<li>Pointer arithmetic</li>
<li>Pointer indexing</li>
<li>Conversion to pointer from an incompatible type</li>
<li>Calling certain C functions, e.g. <code>free</code>, <code>strlen</code> and <code>strncmp</code>.</li>
</ul>
<p>To mark potentially memory-unsafe operations, enclose them in an <code>unsafe</code> block:</p>
<div class="language-v">// allocate 2 uninitialized bytes & return a reference to them
mut p := unsafe { malloc(2) }
p[0] = `h` // Error: pointer indexing is only allowed in `unsafe` blocks
unsafe {
p[0] = `h` // OK
p[1] = `i`
}
p++ // Error: pointer arithmetic is only allowed in `unsafe` blocks
unsafe {
p++ // OK
}
assert *p == `i`
</div>
<p>Best practice is to avoid putting memory-safe expressions inside an <code>unsafe</code> block,
so that the reason for using <code>unsafe</code> is as clear as possible. Generally any code
you think is memory-safe should not be inside an <code>unsafe</code> block, so the compiler
can verify it.</p>
<p>If you suspect your program does violate memory-safety, you have a head start on
finding the cause: look at the <code>unsafe</code> blocks (and how they interact with
surrounding code).</p>
<blockquote class="tip">
<p>[!NOTE]
This is work in progress.</p>
</blockquote>
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