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>Lesson 2: Arguments</a
>
</li>
<li>
<a href="lesson-3.html" class="action-button"
>Lesson 3: Basic Templates</a
>
</li>
</ol>
</div>
<div class="column-divider"></div>

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<h1>
<a class="root-link" href=".">Learn C++ Itanium Symbol Mangling</a>
</h1>
<h2>Lesson 2: Lesson 2: Arguments</h2>
<h2>Lesson 2: Arguments</h2>
<noscript>
<p>
Warning: You have JavaScript disabled. While the content is still
@ -180,12 +180,14 @@ void name(unsigned long long a, unsigned short b, char c, int d) {}
<section data-step="3" class="step">
<p>
Good job! You have now learnt about the mangling of basic types.
</p>
<p class="lesson-last-paragraph">
This is the last lesson that has been written so far. More lessons
may appear in the future.
Good job! You have now learnt about the mangling of basic types. In
the next lesson, we will use there types as template arguments.
</p>
<div class="center">
<a href="lesson-2.html" class="action-button">
Lesson 3: Basic Templates
</a>
</div>
</section>
</div>
</main>

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<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8" />
<meta name="viewport" content="width=device-width, initial-scale=1.0" />
<link rel="stylesheet" href="index.css" />
<title>Womangling</title>
</head>
<body>
<main class="main">
<div class="content" id="content-area">
<h1>
<a class="root-link" href=".">Learn C++ Itanium Symbol Mangling</a>
</h1>
<h2>Lesson 3: Basic Templates</h2>
<noscript>
<p>
Warning: You have JavaScript disabled. While the content is still
viewable, interactive exercises will not work. Consider enabling
JavaScript for this website.
</p>
</noscript>
<!-- https://itanium-cxx-abi.github.io/cxx-abi/abi.html#mangle.function-type -->
<section data-step="0" class="step">
<p>
In this lesson we will look at C++'s most important features and
another big motivation of why symbol mangling exists and is as
complicated as it is: templates.
</p>
<p>
If you're not familiar with templates already, templates provide a
way to write a function that is generic over a type (or value, which
we will get to later). It can then be instantiated with different
types and change its behavior depending on which type it was
instantiated with.
</p>
<pre class="code">
template&lt;typename T&gt;
void empty(T a) {}
</pre>
<p>
Here we create an empty function that takes an argument of type
<code>T</code>, where <code>T</code> is a template parameter. We can
call <code>empty</code> with all sorts of types.
</p>
<pre class="code">
int main() {
empty(0); // T=int
empty("0"); // T=const char*
empty(0l); // T=long
}
</pre>
<p>
For every call with a unique type, the compiler will essentially
copy-paste the function and fill in the concrete template. So for
every different type, there's a different <i>instantiation</i>. The
symbol mangling scheme must ensure that different instantiations get
different symbols, otherwise we coul get conflicts between different
instantiations. This is achieved by encoding the template parameters
into the symbol.
</p>
<p>
The way this is handled is by wrapping all the arguments between a
<code>I</code> (you can remember it as "instantiation") and
<code>E</code> (end) and appending this to the name, before the type
of the function.
</p>
<p>
We will also learn about a new type, the template parameter type,
used to encode the parameter of the example function above. Template
parameter types are not encoded as their instantiated types, but as
a "parameter type". The first template parameter type is denoted
with a
<code>T</code> followed by an underscore.
</p>
<p>
One last thing: templated functions include the
<b>return type</b> as the first type in the argument list.
</p>
<p>
With this, our example instantiation below will have the following
mangled symbol: <code>_Z5emptyIiEvT_</code>.
</p>
<pre class="code">
template&lt;typename T&gt;
void empty(T a) {}
int main() {
empty(0); // T=int
}
</pre>
<ul>
<li><code>_Z5empty</code>: prefix and function name</li>
<li><code>I</code>: start of template arguments</li>
<li><code>i</code>: template argument of type <coed>int</coed></li>
<li><code>E</code>: end of template arguments</li>
<li>
<code>v</code>: return type of the function, <code>void</code>
</li>
<li>
<code>T_</code>: first argument of the function, the first
template parameter (which is instanitated as <code>int</code>, but
that isn't stored in the symbol for efficiency)
</li>
</ul>
<div class="quiz-section">
<p>
What is the mangled symbol of the following instantiation of
empty?
</p>
<pre class="code">
template&lt;typename T&gt;
T empty() {}
int main() {
empty&lt;long&gt;(); // T=long
}
</pre>
<form data-challenge="1" data-answer="_Z5emptyIlET_v">
<input class="quiz-input" />
<button
data-challenge-submit="1"
data-hint="Don't forget about the return type, which is T_"
class="submit-challenge"
type="submit"
>
Answer
</button>
<div class="error"></div>
</form>
</div>
</section>
<section data-step="1" class="step">
<p class="lesson-last-paragraph">
This lesson is still work in progress, further steps will follow in
the future.
</p>
</section>
</div>
</main>
<script>
window.LESSON = 3;
</script>
<script type="module" src="lessons.js"></script>
</body>
</html>