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<!DOCTYPE html>
<html>
<head>
<title>
Coding style
</title>
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<section id="coding-style">
<span id="develop-codingstyle"></span><h1>Coding style<a class="headerlink" href="#coding-style" title="Link to this heading">¶</a></h1>
<p>This page contains various rules, which anyone working on OpenCOR should respect.
These rules were taken (paraphrased, if not simply copied/pasted) from the <a class="reference external" href="https://wiki.qt.io/Coding_Conventions">Qt Coding Conventions</a> document.</p>
<section id="general">
<h2>General<a class="headerlink" href="#general" title="Link to this heading">¶</a></h2>
<ul class="simple">
<li><p>The most important rule of all: the <a class="reference external" href="https://en.wikipedia.org/wiki/KISS_principle">KISS principle</a>, i.e. <em>Keep it simple, stupid!</em>
Always use a simple implementation in favour of a more complicated one.
This eases maintenance a lot!</p></li>
<li><p>Write good C++ code: readable, well commented when necessary, and object-oriented.</p></li>
<li><p>Adapt the code to the structures already existing in OpenCOR or, in the case that you have a better idea, discuss it with the <a class="reference external" href="https://opencor.ws/team.html">project manager</a> before implementing it.</p></li>
<li><p>Take advantage of <a class="reference external" href="https://qt.io/">Qt</a>. Do not re-invent the wheel.</p></li>
</ul>
</section>
<section id="code-constructs">
<h2>Code constructs<a class="headerlink" href="#code-constructs" title="Link to this heading">¶</a></h2>
<p>The following guidelines exist to make the code faster, clearer, and/or to take advantage of the strong type checking in C++.</p>
<ul>
<li><p>Declaration of variables should wait as long as possible.
The rule is: <em>do not declare it until you need it</em>.
In C++, there are a lot of user defined types, and these can very often be expensive to initialise.</p></li>
<li><p>Make the scope of a variable as small as possible.</p></li>
<li><p>Prefer pre-increment to post-increment whenever possible.
Pre-increment has potential of being faster than post-increment.
This rule applies to decrement too.</p>
<div class="good highlight-c++ notranslate"><div class="highlight"><pre><span></span><span class="o">++</span><span class="n">i</span><span class="p">;</span>
<span class="o">--</span><span class="n">j</span><span class="p">;</span>
</pre></div>
</div>
<div class="bad highlight-c++ notranslate"><div class="highlight"><pre><span></span><span class="n">i</span><span class="o">++</span><span class="p">;</span>
<span class="n">j</span><span class="o">--</span><span class="p">;</span>
</pre></div>
</div>
</li>
<li><p>Try to minimise the evaluation of the same code, especially in loops:</p>
<div class="good highlight-c++ notranslate"><div class="highlight"><pre><span></span><span class="k">for</span><span class="w"> </span><span class="p">(</span><span class="n">Container</span><span class="o">::</span><span class="n">iterator</span><span class="w"> </span><span class="n">iter</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">large</span><span class="p">.</span><span class="n">begin</span><span class="p">(),</span><span class="w"> </span><span class="n">end</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">large</span><span class="p">.</span><span class="n">end</span><span class="p">();</span><span class="w"> </span><span class="n">iter</span><span class="w"> </span><span class="o">!=</span><span class="w"> </span><span class="n">end</span><span class="p">;</span><span class="w"> </span><span class="o">++</span><span class="n">iter</span><span class="p">)</span><span class="w"> </span><span class="p">{</span>
<span class="w"> </span><span class="p">...</span>
<span class="p">}</span>
</pre></div>
</div>
<div class="bad highlight-c++ notranslate"><div class="highlight"><pre><span></span><span class="k">for</span><span class="w"> </span><span class="p">(</span><span class="n">Container</span><span class="o">::</span><span class="n">iterator</span><span class="w"> </span><span class="n">iter</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">large</span><span class="p">.</span><span class="n">begin</span><span class="p">();</span><span class="w"> </span><span class="n">iter</span><span class="w"> </span><span class="o">!=</span><span class="w"> </span><span class="n">large</span><span class="p">.</span><span class="n">end</span><span class="p">();</span><span class="w"> </span><span class="o">++</span><span class="n">iter</span><span class="p">)</span><span class="w"> </span><span class="p">{</span>
<span class="w"> </span><span class="p">...</span>
<span class="p">}</span>
</pre></div>
</div>
</li>
<li><p>You should use the range-based <code class="docutils literal notranslate"><span class="pre">for</span></code> loop rather than the Qt <code class="docutils literal notranslate"><span class="pre">foreach</span></code> loop or even the classical <code class="docutils literal notranslate"><span class="pre">for</span></code> loop:</p>
<div class="good highlight-c++ notranslate"><div class="highlight"><pre><span></span><span class="k">for</span><span class="w"> </span><span class="p">(</span><span class="k">auto</span><span class="w"> </span><span class="n">widget</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">container</span><span class="p">)</span><span class="w"> </span><span class="p">{</span>
<span class="w"> </span><span class="n">doSomething</span><span class="p">(</span><span class="n">widget</span><span class="p">);</span>
<span class="p">}</span>
</pre></div>
</div>
<div class="bad highlight-c++ notranslate"><div class="highlight"><pre><span></span><span class="n">foreach</span><span class="w"> </span><span class="p">(</span><span class="n">QWidget</span><span class="w"> </span><span class="o">*</span><span class="n">widget</span><span class="p">,</span><span class="w"> </span><span class="n">container</span><span class="p">)</span><span class="w"> </span><span class="p">{</span>
<span class="w"> </span><span class="n">doSomething</span><span class="p">(</span><span class="n">widget</span><span class="p">);</span>
<span class="p">}</span>
</pre></div>
</div>
<div class="bad highlight-c++ notranslate"><div class="highlight"><pre><span></span><span class="k">for</span><span class="w"> </span><span class="p">(</span><span class="n">Container</span><span class="o">::</span><span class="n">iterator</span><span class="w"> </span><span class="n">iter</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">container</span><span class="p">.</span><span class="n">begin</span><span class="p">(),</span><span class="w"> </span><span class="n">end</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">container</span><span class="p">.</span><span class="n">end</span><span class="p">();</span><span class="w"> </span><span class="n">iter</span><span class="w"> </span><span class="o">!=</span><span class="w"> </span><span class="n">end</span><span class="p">;</span><span class="w"> </span><span class="o">++</span><span class="n">iter</span><span class="p">)</span><span class="w"> </span><span class="p">{</span>
<span class="w"> </span><span class="n">doSomething</span><span class="p">(</span><span class="o">*</span><span class="n">iter</span><span class="p">);</span>
<span class="p">}</span>
</pre></div>
</div>
<p>Make the loop variable <code class="docutils literal notranslate"><span class="pre">const</span></code>, if possible.
This might prevent unnecessary detaching of shared data.</p>
<div class="good highlight-c++ notranslate"><div class="highlight"><pre><span></span><span class="k">for</span><span class="w"> </span><span class="p">(</span><span class="k">const</span><span class="w"> </span><span class="k">auto</span><span class="w"> </span><span class="o">&</span><span class="n">name</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">someListOfNames</span><span class="p">)</span><span class="w"> </span><span class="p">{</span>
<span class="w"> </span><span class="n">doSomething</span><span class="p">(</span><span class="n">name</span><span class="p">);</span>
<span class="p">}</span>
</pre></div>
</div>
<div class="bad highlight-c++ notranslate"><div class="highlight"><pre><span></span><span class="k">for</span><span class="w"> </span><span class="p">(</span><span class="k">auto</span><span class="w"> </span><span class="n">name</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="n">someListOfNames</span><span class="p">)</span><span class="w"> </span><span class="p">{</span>
<span class="w"> </span><span class="n">doSomething</span><span class="p">(</span><span class="n">name</span><span class="p">);</span>
<span class="p">}</span>
</pre></div>
</div>
</li>
</ul>
</section>
<section id="formatting">
<h2>Formatting<a class="headerlink" href="#formatting" title="Link to this heading">¶</a></h2>
<ul>
<li><p>Indentation: 4 spaces, no tabulations.</p></li>
<li><p><strong>Naming rules:</strong></p>
<ul>
<li><p>Use descriptive, simple and short names.</p></li>
<li><p>Single character variable names are only okay for counters and temporaries where the purpose of the variable is obvious.</p>
<div class="good highlight-c++ notranslate"><div class="highlight"><pre><span></span><span class="kt">int</span><span class="w"> </span><span class="n">width</span><span class="p">;</span>
<span class="kt">int</span><span class="w"> </span><span class="n">height</span><span class="p">;</span>
<span class="kt">char</span><span class="w"> </span><span class="o">*</span><span class="n">nameOfThis</span><span class="p">;</span>
<span class="kt">char</span><span class="w"> </span><span class="o">*</span><span class="n">nameOfThat</span><span class="p">;</span>
</pre></div>
</div>
<div class="bad highlight-c++ notranslate"><div class="highlight"><pre><span></span><span class="kt">int</span><span class="w"> </span><span class="n">a</span><span class="p">,</span><span class="w"> </span><span class="n">b</span><span class="p">;</span>
<span class="kt">char</span><span class="w"> </span><span class="o">*</span><span class="n">c</span><span class="p">,</span><span class="w"> </span><span class="o">*</span><span class="n">d</span><span class="p">;</span>
</pre></div>
</div>
</li>
<li><p>Class names and enums start with an upper-case letter while variables and functions start with a lower-case letter.
Each consecutive word in a name starts with an upper-case letter.</p>
<div class="good highlight-c++ notranslate"><div class="highlight"><pre><span></span><span class="k">class</span><span class="w"> </span><span class="nc">MainWindow</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="k">public</span><span class="w"> </span><span class="n">QMainWindow</span>
<span class="p">{</span>
<span class="w"> </span><span class="p">...</span>
<span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="n">mVariable</span><span class="p">;</span>
<span class="w"> </span><span class="p">...</span>
<span class="w"> </span><span class="kt">void</span><span class="w"> </span><span class="n">function</span><span class="p">();</span>
<span class="w"> </span><span class="p">...</span>
<span class="p">}</span>
</pre></div>
</div>
<div class="bad highlight-c++ notranslate"><div class="highlight"><pre><span></span><span class="k">class</span><span class="w"> </span><span class="nc">mainWindow</span><span class="w"> </span><span class="o">:</span><span class="w"> </span><span class="k">public</span><span class="w"> </span><span class="n">QMainWindow</span>
<span class="p">{</span>
<span class="w"> </span><span class="p">...</span>
<span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="n">Variable</span><span class="p">;</span>
<span class="w"> </span><span class="p">...</span>
<span class="w"> </span><span class="kt">void</span><span class="w"> </span><span class="n">Function</span><span class="p">();</span>
<span class="w"> </span><span class="p">...</span>
<span class="p">}</span>
</pre></div>
</div>
<p><strong>Note:</strong> class variables start with a lower-case <code class="docutils literal notranslate"><span class="pre">m</span></code>.</p>
</li>
<li><p>Parameters passed to a function start with a lower-case <code class="docutils literal notranslate"><span class="pre">p</span></code>, but not local variables.</p>
<div class="good highlight-c++ notranslate"><div class="highlight"><pre><span></span><span class="kt">int</span><span class="w"> </span><span class="nf">main</span><span class="p">(</span><span class="kt">int</span><span class="w"> </span><span class="n">pArgC</span><span class="p">,</span><span class="w"> </span><span class="kt">char</span><span class="w"> </span><span class="o">*</span><span class="n">pArgV</span><span class="p">[])</span>
<span class="p">{</span>
<span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="n">someVariable</span><span class="p">;</span>
<span class="w"> </span><span class="p">...</span>
<span class="p">}</span>
</pre></div>
</div>
<div class="bad highlight-c++ notranslate"><div class="highlight"><pre><span></span><span class="kt">int</span><span class="w"> </span><span class="nf">main</span><span class="p">(</span><span class="kt">int</span><span class="w"> </span><span class="n">argc</span><span class="p">,</span><span class="w"> </span><span class="kt">char</span><span class="w"> </span><span class="o">*</span><span class="n">argv</span><span class="p">[])</span>
<span class="p">{</span>
<span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="n">pSomeVariable</span><span class="p">;</span>
<span class="w"> </span><span class="p">...</span>
<span class="p">}</span>
</pre></div>
</div>
</li>
</ul>
</li>
<li><p><strong>Declarations:</strong></p>
<ul>
<li><p>Use this order for the access sections of your class: <code class="docutils literal notranslate"><span class="pre">public</span></code>, <code class="docutils literal notranslate"><span class="pre">protected</span></code>, and <code class="docutils literal notranslate"><span class="pre">private</span></code>.
The <code class="docutils literal notranslate"><span class="pre">public</span></code> section is of interest for every user of the class.
The <code class="docutils literal notranslate"><span class="pre">private</span></code> section is only of interest for the implementors of the class.</p></li>
<li><p>Avoid declaring global objects in the declaration file of the class.
If the same variable is used for all objects, use a <code class="docutils literal notranslate"><span class="pre">static</span></code> member.</p></li>
<li><p>Avoid declaring global or static variables.</p></li>
<li><p>Use only one declaration per line:</p>
<div class="good highlight-c++ notranslate"><div class="highlight"><pre><span></span><span class="kt">int</span><span class="w"> </span><span class="n">width</span><span class="p">;</span>
<span class="kt">int</span><span class="w"> </span><span class="n">height</span><span class="p">;</span>
</pre></div>
</div>
<div class="bad highlight-c++ notranslate"><div class="highlight"><pre><span></span><span class="kt">int</span><span class="w"> </span><span class="n">width</span><span class="p">,</span><span class="w"> </span><span class="n">height</span><span class="p">;</span>
</pre></div>
</div>
<p>This is especially important when initialisation is done at the same time:</p>
<div class="good highlight-c++ notranslate"><div class="highlight"><pre><span></span><span class="n">QString</span><span class="w"> </span><span class="n">firstName</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="s">"Joe"</span><span class="p">;</span>
<span class="n">QString</span><span class="w"> </span><span class="n">lastName</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="s">"Foo"</span><span class="p">;</span>
</pre></div>
</div>
<div class="bad highlight-c++ notranslate"><div class="highlight"><pre><span></span><span class="n">QString</span><span class="w"> </span><span class="n">firstName</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="s">"Joe"</span><span class="p">,</span><span class="w"> </span><span class="n">lastName</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="s">"Foo"</span><span class="p">;</span>
</pre></div>
</div>
<p><strong>Note:</strong> <code class="docutils literal notranslate"><span class="pre">QString</span> <span class="pre">firstName</span> <span class="pre">=</span> <span class="pre">"Joe";</span></code> is formally calling a copy constructor on a temporary string constructed from a string literal and therefore has the potential of being more expensive than direct construction by <code class="docutils literal notranslate"><span class="pre">QString</span> <span class="pre">firstName("joe")</span></code>.
However, the compiler is allowed to elide the copy (even if it has side effects), and modern compilers typically do so.
Given these equal costs, OpenCOR code favours the <code class="docutils literal notranslate"><span class="pre">=</span></code> idiom as it is in line with the traditional C-style initialisation, and cannot be mistaken as a function declaration, and reduces the level of nested parantheses in more initialisations.</p>
</li>
</ul>
</li>
<li><p>Pointers and references:</p>
<div class="good highlight-c++ notranslate"><div class="highlight"><pre><span></span><span class="kt">char</span><span class="w"> </span><span class="o">*</span><span class="n">ptr</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="s">"flop"</span><span class="p">;</span>
<span class="kt">char</span><span class="w"> </span><span class="o">&</span><span class="n">c</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="o">*</span><span class="n">ptr</span><span class="p">;</span>
</pre></div>
</div>
<div class="bad highlight-c++ notranslate"><div class="highlight"><pre><span></span><span class="kt">char</span><span class="o">*</span><span class="w"> </span><span class="n">ptr</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="s">"flop"</span><span class="p">;</span>
<span class="kt">char</span><span class="w"> </span><span class="o">&</span><span class="w"> </span><span class="n">c</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="n">ptr</span><span class="p">;</span>
</pre></div>
</div>
<p>Also, we will have:</p>
<div class="good highlight-c++ notranslate"><div class="highlight"><pre><span></span><span class="k">const</span><span class="w"> </span><span class="kt">char</span><span class="w"> </span><span class="o">*</span><span class="n">ptr</span><span class="p">;</span>
</pre></div>
</div>
<div class="bad highlight-c++ notranslate"><div class="highlight"><pre><span></span><span class="kt">char</span><span class="w"> </span><span class="k">const</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="n">ptr</span><span class="p">;</span>
</pre></div>
</div>
<p>Use <code class="docutils literal notranslate"><span class="pre">nullptr</span></code> for null pointer constants:</p>
<div class="good highlight-c++ notranslate"><div class="highlight"><pre><span></span><span class="kt">void</span><span class="w"> </span><span class="o">*</span><span class="n">ptr</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="k">nullptr</span><span class="p">;</span>
</pre></div>
</div>
<div class="bad highlight-c++ notranslate"><div class="highlight"><pre><span></span><span class="kt">void</span><span class="w"> </span><span class="o">*</span><span class="n">ptr</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">0</span><span class="p">;</span>
<span class="kt">void</span><span class="w"> </span><span class="o">*</span><span class="n">ptr</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="nb">NULL</span><span class="p">;</span>
<span class="kt">void</span><span class="w"> </span><span class="o">*</span><span class="n">ptr</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="sc">'\0'</span><span class="p">;</span>
<span class="kt">void</span><span class="w"> </span><span class="o">*</span><span class="n">ptr</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">42-7</span><span class="o">*</span><span class="mi">6</span><span class="p">;</span>
</pre></div>
</div>
</li>
<li><p><strong>Whitespace:</strong></p>
<ul>
<li><p>Use blank lines to group statements together where suited.</p></li>
<li><p>Always use only one blank line.</p></li>
<li><p>Operator names and parentheses: do not use spaces between operator names and function names.
The <code class="docutils literal notranslate"><span class="pre">==</span></code> is part of the function name, and therefore, spaces make the declaration look like an expression:</p>
<div class="good highlight-c++ notranslate"><div class="highlight"><pre><span></span><span class="k">operator</span><span class="o">==</span><span class="p">(</span><span class="n">type</span><span class="p">)</span>
</pre></div>
</div>
<div class="bad highlight-c++ notranslate"><div class="highlight"><pre><span></span><span class="k">operator</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="p">(</span><span class="n">type</span><span class="p">)</span>
</pre></div>
</div>
</li>
<li><p>Function names and parentheses: do not use spaces between function names and parentheses:</p>
<div class="good highlight-c++ notranslate"><div class="highlight"><pre><span></span><span class="kt">void</span><span class="w"> </span><span class="n">mangle</span><span class="p">()</span>
</pre></div>
</div>
<div class="bad highlight-c++ notranslate"><div class="highlight"><pre><span></span><span class="kt">void</span><span class="w"> </span><span class="n">mangle</span><span class="w"> </span><span class="p">()</span>
</pre></div>
</div>
</li>
<li><p>Always use a single space after a keyword, and before a curly brace:</p>
<div class="good highlight-c++ notranslate"><div class="highlight"><pre><span></span><span class="k">if</span><span class="w"> </span><span class="p">(</span><span class="n">foo</span><span class="p">)</span><span class="w"> </span><span class="p">{</span>
<span class="p">}</span>
</pre></div>
</div>
<div class="bad highlight-c++ notranslate"><div class="highlight"><pre><span></span><span class="k">if</span><span class="p">(</span><span class="n">foo</span><span class="p">){</span>
<span class="p">}</span>
</pre></div>
</div>
</li>
<li><p>For pointers or references, always use a single space before <code class="docutils literal notranslate"><span class="pre">*</span></code> or <code class="docutils literal notranslate"><span class="pre">&</span></code>, but never after.</p>
<div class="good highlight-c++ notranslate"><div class="highlight"><pre><span></span><span class="kt">int</span><span class="w"> </span><span class="o">*</span><span class="n">var1</span><span class="p">;</span>
<span class="kt">int</span><span class="w"> </span><span class="o">&</span><span class="n">var2</span><span class="p">;</span>
</pre></div>
</div>
<div class="bad highlight-c++ notranslate"><div class="highlight"><pre><span></span><span class="kt">int</span><span class="o">*</span><span class="w"> </span><span class="n">var1</span><span class="p">;</span>
<span class="kt">int</span><span class="o">&</span><span class="w"> </span><span class="n">var2</span><span class="p">;</span>
</pre></div>
</div>
</li>
</ul>
</li>
<li><p><strong>Braces:</strong></p>
<ul>
<li><p>As a base rule, place the left curly brace on the same line as the start of the statement:</p>
<div class="good highlight-c++ notranslate"><div class="highlight"><pre><span></span><span class="k">if</span><span class="w"> </span><span class="p">(</span><span class="n">codec</span><span class="p">)</span><span class="w"> </span><span class="p">{</span>
<span class="p">}</span>
</pre></div>
</div>
<div class="bad highlight-c++ notranslate"><div class="highlight"><pre><span></span><span class="k">if</span><span class="w"> </span><span class="p">(</span><span class="n">codec</span><span class="p">)</span>
<span class="p">{</span>
<span class="p">}</span>
</pre></div>
</div>
<p><strong>Exception:</strong> function implementations and class declarations always have the left curly brace in the beginning of a line:</p>
<div class="good highlight-c++ notranslate"><div class="highlight"><pre><span></span><span class="k">class</span><span class="w"> </span><span class="nc">Moo</span>
<span class="p">{</span>
<span class="p">};</span>
</pre></div>
</div>
<div class="bad highlight-c++ notranslate"><div class="highlight"><pre><span></span><span class="k">class</span><span class="w"> </span><span class="nc">Moo</span><span class="w"> </span><span class="p">{</span>
<span class="p">};</span>
</pre></div>
</div>
<div class="good highlight-c++ notranslate"><div class="highlight"><pre><span></span><span class="kt">void</span><span class="w"> </span><span class="nf">Moo::foo</span><span class="p">()</span>
<span class="p">{</span>
<span class="p">}</span>
</pre></div>
</div>
<div class="bad highlight-c++ notranslate"><div class="highlight"><pre><span></span><span class="kt">void</span><span class="w"> </span><span class="nf">Moo::foo</span><span class="p">()</span><span class="w"> </span><span class="p">{</span>
<span class="p">}</span>
</pre></div>
</div>
</li>
<li><p>Use curly braces at all times:</p>
<div class="good highlight-c++ notranslate"><div class="highlight"><pre><span></span><span class="k">if</span><span class="w"> </span><span class="p">(</span><span class="n">address</span><span class="p">.</span><span class="n">isEmpty</span><span class="p">())</span><span class="w"> </span><span class="p">{</span>
<span class="w"> </span><span class="k">return</span><span class="w"> </span><span class="nb">false</span><span class="p">;</span>
<span class="p">}</span>
</pre></div>
</div>
<div class="bad highlight-c++ notranslate"><div class="highlight"><pre><span></span><span class="k">if</span><span class="w"> </span><span class="p">(</span><span class="n">address</span><span class="p">.</span><span class="n">isEmpty</span><span class="p">())</span>
<span class="w"> </span><span class="k">return</span><span class="w"> </span><span class="nb">false</span><span class="p">;</span>
</pre></div>
</div>
<div class="good highlight-c++ notranslate"><div class="highlight"><pre><span></span><span class="k">for</span><span class="w"> </span><span class="p">(</span><span class="kt">int</span><span class="w"> </span><span class="n">i</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">0</span><span class="p">;</span><span class="w"> </span><span class="n">i</span><span class="w"> </span><span class="o"><</span><span class="w"> </span><span class="mi">10</span><span class="p">;</span><span class="w"> </span><span class="o">++</span><span class="n">i</span><span class="p">)</span><span class="w"> </span><span class="p">{</span>
<span class="w"> </span><span class="n">qDebug</span><span class="p">(</span><span class="s">"%d"</span><span class="p">,</span><span class="w"> </span><span class="n">i</span><span class="p">);</span>
<span class="p">}</span>
</pre></div>
</div>
<div class="bad highlight-c++ notranslate"><div class="highlight"><pre><span></span><span class="k">for</span><span class="w"> </span><span class="p">(</span><span class="kt">int</span><span class="w"> </span><span class="n">i</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">0</span><span class="p">;</span><span class="w"> </span><span class="n">i</span><span class="w"> </span><span class="o"><</span><span class="w"> </span><span class="mi">10</span><span class="p">;</span><span class="w"> </span><span class="o">++</span><span class="n">i</span><span class="p">)</span>
<span class="w"> </span><span class="n">qDebug</span><span class="p">(</span><span class="s">"%d"</span><span class="p">,</span><span class="w"> </span><span class="n">i</span><span class="p">);</span>
</pre></div>
</div>
</li>
<li><p>Use curly braces when the body of a conditional statement is empty:</p>
<div class="good highlight-c++ notranslate"><div class="highlight"><pre><span></span><span class="k">while</span><span class="w"> </span><span class="p">(</span><span class="n">cond</span><span class="p">)</span><span class="w"> </span><span class="p">{</span>
<span class="p">}</span>
</pre></div>
</div>
<div class="bad highlight-c++ notranslate"><div class="highlight"><pre><span></span><span class="k">while</span><span class="w"> </span><span class="p">(</span><span class="n">cond</span><span class="p">);</span>
</pre></div>
</div>
</li>
</ul>
</li>
<li><p>Parentheses: use parentheses to group expressions:</p>
<div class="good highlight-c++ notranslate"><div class="highlight"><pre><span></span><span class="k">if</span><span class="w"> </span><span class="p">((</span><span class="n">cond1</span><span class="w"> </span><span class="o">&&</span><span class="w"> </span><span class="n">cond2</span><span class="p">)</span><span class="w"> </span><span class="o">||</span><span class="w"> </span><span class="n">cond3</span><span class="p">)</span>
</pre></div>
</div>
<div class="bad highlight-c++ notranslate"><div class="highlight"><pre><span></span><span class="k">if</span><span class="w"> </span><span class="p">(</span><span class="n">cond1</span><span class="w"> </span><span class="o">&&</span><span class="w"> </span><span class="n">cond2</span><span class="w"> </span><span class="o">||</span><span class="w"> </span><span class="n">cond3</span><span class="p">)</span>
</pre></div>
</div>
<div class="good highlight-c++ notranslate"><div class="highlight"><pre><span></span><span class="p">(</span><span class="n">var1</span><span class="o">+</span><span class="n">var2</span><span class="p">)</span><span class="w"> </span><span class="o">&</span><span class="w"> </span><span class="n">var3</span>
</pre></div>
</div>
<div class="bad highlight-c++ notranslate"><div class="highlight"><pre><span></span><span class="n">var1</span><span class="o">+</span><span class="n">var2</span><span class="w"> </span><span class="o">&</span><span class="w"> </span><span class="n">var3</span>
</pre></div>
</div>
</li>
<li><p><strong>Line Breaks:</strong></p>
<ul>
<li><p>Keep lines shorter than 80 characters whenever possible.</p>
<p><strong>Note:</strong> <a class="reference external" href="https://qt.io/product/development-tools">Qt Creator</a> can be configured to display a right margin.
For this, select the <code class="docutils literal notranslate"><span class="pre">Edit</span></code> | <code class="docutils literal notranslate"><span class="pre">Preferences...</span></code> menu, then the <code class="docutils literal notranslate"><span class="pre">Text</span> <span class="pre">Editor</span></code> section, and finally the <code class="docutils literal notranslate"><span class="pre">Display</span></code> tab.
Configuration options can be found under the <code class="docutils literal notranslate"><span class="pre">Text</span> <span class="pre">Wrapping</span></code> group box.</p>
</li>
<li><p>Insert line breaks if necessary.</p></li>
<li><p>Commas go at the end of a broken line.</p></li>
<li><p>Operators start at the beginning of a new line.</p>
<div class="good highlight-c++ notranslate"><div class="highlight"><pre><span></span><span class="k">if</span><span class="w"> </span><span class="p">(</span><span class="w"> </span><span class="n">longExpression</span>
<span class="w"> </span><span class="o">||</span><span class="w"> </span><span class="n">otherLongExpression</span>
<span class="w"> </span><span class="o">||</span><span class="w"> </span><span class="n">otherOtherLongExpression</span><span class="p">)</span><span class="w"> </span><span class="p">{</span>
<span class="p">}</span>
</pre></div>
</div>
<div class="bad highlight-c++ notranslate"><div class="highlight"><pre><span></span><span class="k">if</span><span class="w"> </span><span class="p">(</span><span class="n">longExpression</span><span class="w"> </span><span class="o">||</span>
<span class="w"> </span><span class="n">otherLongExpression</span><span class="w"> </span><span class="o">||</span>
<span class="w"> </span><span class="n">otherOtherLongExpression</span><span class="p">)</span><span class="w"> </span><span class="p">{</span>
<span class="p">}</span>
</pre></div>
</div>
</li>
</ul>
</li>
</ul>
</section>
<section id="patterns-and-practices">
<h2>Patterns and practices<a class="headerlink" href="#patterns-and-practices" title="Link to this heading">¶</a></h2>
<ul>
<li><p>Do not use exceptions, unless you know what you are doing.</p></li>
<li><p>Do not use RTTI (Run-Time Type Information, i.e. the <code class="docutils literal notranslate"><span class="pre">typeinfo</span> <span class="pre">struct</span></code>, the <code class="docutils literal notranslate"><span class="pre">dynamic_cast</span></code> or the <code class="docutils literal notranslate"><span class="pre">typeid</span></code> operators, including throwing exceptions), unless you know what you are doing.</p></li>
<li><p>Use templates wisely, not just because you can.</p></li>
<li><p>Every <code class="docutils literal notranslate"><span class="pre">QObject</span></code> subclass must have a <code class="docutils literal notranslate"><span class="pre">Q_OBJECT</span></code> macro, even if it does not have signals or slots, if it is intended to be used with <code class="docutils literal notranslate"><span class="pre">qobject_cast<></span></code>.</p></li>
<li><p>If you create a new set of <code class="docutils literal notranslate"><span class="pre">.cpp</span></code>/<code class="docutils literal notranslate"><span class="pre">.h</span></code> files, then our copyright statement and a comment common to both files should be included at the beginning of those files (e.g., <a class="reference external" href="https://github.com/opencor/opencor/blob/master/src/mainwindow.cpp"><code class="docutils literal notranslate"><span class="pre">[OpenCOR]/src/mainwindow.cpp</span></code></a> and <a class="reference external" href="https://github.com/opencor/opencor/blob/master/src/mainwindow.h"><code class="docutils literal notranslate"><span class="pre">[OpenCOR]/src/mainwindow.h</span></code></a>).</p></li>
<li><p><strong>Including headers:</strong></p>
<ul>
<li><p>Arrange headers in alphabetic order within a block:</p>
<div class="good highlight-c++ notranslate"><div class="highlight"><pre><span></span><span class="cp">#include</span><span class="w"> </span><span class="cpf"><QCoreApplication></span>
<span class="cp">#include</span><span class="w"> </span><span class="cpf"><QMessageBox></span>
<span class="cp">#include</span><span class="w"> </span><span class="cpf"><QSettings></span>
</pre></div>
</div>
<div class="bad highlight-c++ notranslate"><div class="highlight"><pre><span></span><span class="cp">#include</span><span class="w"> </span><span class="cpf"><QSettings></span>
<span class="cp">#include</span><span class="w"> </span><span class="cpf"><QCoreApplication></span>
<span class="cp">#include</span><span class="w"> </span><span class="cpf"><QMessageBox></span>
</pre></div>
</div>
</li>
<li><p>Arrange includes in blocks of headers that are specific to OpenCOR, <a class="reference external" href="https://qt.io/">Qt</a>, third-party libraries and C++.
For example:</p>
<div class="highlight-c++ notranslate"><div class="highlight"><pre><span></span><span class="cp">#include</span><span class="w"> </span><span class="cpf">"coreguiutils.h"</span>
<span class="cp">#include</span><span class="w"> </span><span class="cpf">"filemanager.h"</span>
<span class="cp">#include</span><span class="w"> </span><span class="cpf"><QApplication></span>
<span class="cp">#include</span><span class="w"> </span><span class="cpf"><QMainWindow></span>
<span class="cp">#include</span><span class="w"> </span><span class="cpf">"qwt_mml_document.h"</span>
<span class="cp">#include</span><span class="w"> </span><span class="cpf">"qwt_wheel.h"</span>
<span class="cp">#include</span><span class="w"> </span><span class="cpf"><string></span>
<span class="cp">#include</span><span class="w"> </span><span class="cpf"><vector></span>
</pre></div>
</div>
</li>
<li><p>Prefer direct includes whenever possible:</p>
<div class="good highlight-c++ notranslate"><div class="highlight"><pre><span></span><span class="cp">#include</span><span class="w"> </span><span class="cpf"><QFileInfo></span>
</pre></div>
</div>
<div class="bad highlight-c++ notranslate"><div class="highlight"><pre><span></span><span class="cp">#include</span><span class="w"> </span><span class="cpf"><QCore/QFileInfo></span>
</pre></div>
</div>
</li>
</ul>
</li>
<li><p><strong>Casting:</strong></p>
<ul class="simple">
<li><p>Avoid C casts, prefer C++ casts (<code class="docutils literal notranslate"><span class="pre">static_cast</span></code>, <code class="docutils literal notranslate"><span class="pre">const_cast</span></code>, <code class="docutils literal notranslate"><span class="pre">reinterpret_cast</span></code>). Both <code class="docutils literal notranslate"><span class="pre">reinterpret_cast</span></code> and C-style casts are dangerous, but at least <code class="docutils literal notranslate"><span class="pre">reinterpret_cast</span></code> will not remove the <code class="docutils literal notranslate"><span class="pre">const</span></code> modifier.</p></li>
<li><p>Do not use <code class="docutils literal notranslate"><span class="pre">dynamic_cast</span></code>, use <code class="docutils literal notranslate"><span class="pre">qobject_cast</span></code> for <code class="docutils literal notranslate"><span class="pre">QObject</span></code>, or refactor your design, for example by introducing a <code class="docutils literal notranslate"><span class="pre">type()</span></code> method (see <a class="reference external" href="https://doc.qt.io/qt-5/qlistwidgetitem.html"><code class="docutils literal notranslate"><span class="pre">QListWidgetItem</span></code></a>), unless you know what you are doing.</p></li>
</ul>
</li>
<li><p><strong>Compiler and platform-specific issues:</strong></p>
<ul>
<li><p>Be extremely careful when using the question mark operator.
If the returned types are not identical, some compilers generate code that crashes at runtime (you will not even get a compiler warning):</p>
<div class="highlight-c++ notranslate"><div class="highlight"><pre><span></span><span class="n">QString</span><span class="w"> </span><span class="n">str</span><span class="p">;</span>
<span class="p">...</span>
<span class="k">return</span><span class="w"> </span><span class="n">condition</span><span class="o">?</span><span class="n">str</span><span class="o">:</span><span class="s">"nothing"</span><span class="p">;</span><span class="w"> </span><span class="c1">// Crash at runtime - QString vs const char *</span>
</pre></div>
</div>
</li>
<li><p>Be extremely careful about alignment.
Whenever a pointer is cast such that the required alignment of the target is increased, the resulting code might crash at runtime on some architectures.
For example, if a <code class="docutils literal notranslate"><span class="pre">const</span> <span class="pre">char</span> <span class="pre">*</span></code> is cast to a <code class="docutils literal notranslate"><span class="pre">const</span> <span class="pre">int</span> <span class="pre">*</span></code>, it will crash on machines where integers have to be aligned at two-byte or four-byte boundaries.
Use a union to force the compiler to align variables correctly.
In the example below, you can be sure that all instances of <code class="docutils literal notranslate"><span class="pre">AlignHelper</span></code> are aligned at integer-boundaries:</p>
<div class="highlight-c++ notranslate"><div class="highlight"><pre><span></span><span class="k">union</span><span class="w"> </span><span class="nc">AlignHelper</span>
<span class="p">{</span>
<span class="w"> </span><span class="kt">char</span><span class="w"> </span><span class="n">c</span><span class="p">;</span>
<span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="n">i</span><span class="p">;</span>
<span class="p">};</span>
</pre></div>
</div>
</li>
<li><p>Anything that has a constructor or needs to run code to be initialised cannot be used as global object in library code since it is undefined when that constructor or code will be run (on first usage, on library load, before <code class="docutils literal notranslate"><span class="pre">main()</span></code> or not at all).
Even if the execution time of the initialiser is defined for shared libraries, you will get into trouble when moving that code in a plugin or if the library is compiled statically:</p>
<div class="bad highlight-c++ notranslate"><div class="highlight"><pre><span></span><span class="c1">// The default constructor needs to be run to initialize x</span>
<span class="k">static</span><span class="w"> </span><span class="k">const</span><span class="w"> </span><span class="n">QString</span><span class="w"> </span><span class="n">x</span><span class="p">;</span>
<span class="c1">// The constructor that takes a const char * has to be run</span>
<span class="k">static</span><span class="w"> </span><span class="k">const</span><span class="w"> </span><span class="n">QString</span><span class="w"> </span><span class="n">s</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="s">"Hello, World!"</span><span class="p">;</span>
<span class="c1">// The call time of foo() is undefined and might not be called at all</span>
<span class="k">static</span><span class="w"> </span><span class="k">const</span><span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="n">i</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">foo</span><span class="p">();</span>
</pre></div>
</div>
<p>Things you can do:</p>
<div class="good highlight-c++ notranslate"><div class="highlight"><pre><span></span><span class="c1">// No constructor must be run, x is set at compile time</span>
<span class="k">static</span><span class="w"> </span><span class="k">const</span><span class="w"> </span><span class="kt">char</span><span class="w"> </span><span class="n">x</span><span class="p">[]</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="s">"someText"</span><span class="p">;</span>
<span class="c1">// y will be set at compile time</span>
<span class="k">static</span><span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="n">y</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">7</span><span class="p">;</span>
<span class="c1">// s will be initialised statically, i.e. no code is run</span>
<span class="k">static</span><span class="w"> </span><span class="n">MyStruct</span><span class="w"> </span><span class="n">s</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="p">{</span><span class="mi">1</span><span class="p">,</span><span class="w"> </span><span class="mi">2</span><span class="p">,</span><span class="w"> </span><span class="mi">3</span><span class="p">};</span>
<span class="c1">// Pointers to objects are OK, no code needs to be run to initialise ptr</span>
<span class="k">static</span><span class="w"> </span><span class="n">QString</span><span class="w"> </span><span class="o">*</span><span class="n">ptr</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="k">nullptr</span><span class="p">;</span>
<span class="c1">// Use Q_GLOBAL_STATIC to create static global objects instead</span>
<span class="n">Q_STATIC_GLOBAL</span><span class="p">(</span><span class="n">QString</span><span class="p">,</span><span class="w"> </span><span class="n">s</span><span class="p">)</span>
<span class="p">...</span>
<span class="kt">void</span><span class="w"> </span><span class="n">foo</span><span class="p">()</span>
<span class="p">{</span>
<span class="w"> </span><span class="n">s</span><span class="p">()</span><span class="o">-></span><span class="n">append</span><span class="p">(</span><span class="s">"moo"</span><span class="p">);</span>
<span class="p">}</span>
</pre></div>
</div>
<p><strong>Note #1:</strong> static objects in function scope are not a problem.
The constructor will be run the first time the function is entered.
The code is not re-entrant, though.</p>
<p><strong>Note #2:</strong> using <a class="reference external" href="https://qt.io/">Qt</a> 5 and <a class="reference external" href="https://en.wikipedia.org/wiki/C++11">C++11</a>, it is now possible to (indirectly) have a <code class="docutils literal notranslate"><span class="pre">static</span> <span class="pre">const</span> <span class="pre">QString</span></code> (see <a class="reference external" href="https://www.macieira.org/blog/2011/07/qstring-improved/">here</a> for more information on <code class="docutils literal notranslate"><span class="pre">QString</span></code>), thus making it possible for a variable to be both read-only and sharable.</p>
<div class="good highlight-c++ notranslate"><div class="highlight"><pre><span></span><span class="k">static</span><span class="w"> </span><span class="k">const</span><span class="w"> </span><span class="k">auto</span><span class="w"> </span><span class="n">s</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">QStringLiteral</span><span class="p">(</span><span class="s">"Hello, World!"</span><span class="p">);</span>
</pre></div>
</div>
<div class="bad highlight-c++ notranslate"><div class="highlight"><pre><span></span><span class="k">static</span><span class="w"> </span><span class="k">const</span><span class="w"> </span><span class="n">QString</span><span class="w"> </span><span class="n">s</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="s">"Hello, World!"</span><span class="p">;</span>
</pre></div>
</div>
</li>
<li><p>A <code class="docutils literal notranslate"><span class="pre">char</span></code> is signed or unsigned, depending on the architecture. Use <code class="docutils literal notranslate"><span class="pre">signed</span> <span class="pre">char</span></code> or <code class="docutils literal notranslate"><span class="pre">uchar</span></code> if you explicitely want a signed or unsigned char.
The following code will break on PowerPC, for example:</p>
<div class="highlight-c++ notranslate"><div class="highlight"><pre><span></span><span class="c1">// The condition is always true on platforms where the default is unsigned</span>
<span class="k">if</span><span class="w"> </span><span class="p">(</span><span class="n">c</span><span class="w"> </span><span class="o">>=</span><span class="w"> </span><span class="mi">0</span><span class="p">)</span><span class="w"> </span><span class="p">{</span>
<span class="w"> </span><span class="p">...</span>
<span class="p">}</span>
</pre></div>
</div>
</li>
<li><p>Avoid 64-bit enum values.
The AAPCS (Procedure Call Standard for the ARM Architecture) embedded ABI hard codes all enum values to a 32-bit integer.</p></li>
<li><p>Do not mix <code class="docutils literal notranslate"><span class="pre">const</span></code> and non-<code class="docutils literal notranslate"><span class="pre">const</span></code> iterators.
This will silently crash on broken compilers.</p>
<div class="good highlight-c++ notranslate"><div class="highlight"><pre><span></span><span class="k">for</span><span class="w"> </span><span class="p">(</span><span class="n">Container</span><span class="o">::</span><span class="n">const_iterator</span><span class="w"> </span><span class="n">iter</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">c</span><span class="p">.</span><span class="n">constBegin</span><span class="p">(),</span><span class="w"> </span><span class="n">end</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">c</span><span class="p">.</span><span class="n">constEnd</span><span class="p">();</span><span class="w"> </span><span class="n">iter</span><span class="w"> </span><span class="o">!=</span><span class="w"> </span><span class="n">end</span><span class="p">;</span><span class="w"> </span><span class="o">++</span><span class="n">iter</span><span class="p">)</span>
</pre></div>
</div>
<div class="bad highlight-c++ notranslate"><div class="highlight"><pre><span></span><span class="k">for</span><span class="w"> </span><span class="p">(</span><span class="n">Container</span><span class="o">::</span><span class="n">const_iterator</span><span class="w"> </span><span class="n">iter</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">c</span><span class="p">.</span><span class="n">begin</span><span class="p">(),</span><span class="w"> </span><span class="n">Container</span><span class="o">::</span><span class="n">iterator</span><span class="w"> </span><span class="n">end</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">c</span><span class="p">.</span><span class="n">end</span><span class="p">();</span><span class="w"> </span><span class="n">iter</span><span class="w"> </span><span class="o">!=</span><span class="w"> </span><span class="n">end</span><span class="p">;</span><span class="w"> </span><span class="o">++</span><span class="n">iter</span><span class="p">)</span>
</pre></div>
</div>
</li>
</ul>
</li>
<li><p>To inherit from template or tool classes has the following potential pitfalls:</p>
<ul class="simple">
<li><p>The destructors are not virtual, which can lead to memory leaks.</p></li>
<li><p>The symbols are not exported (and mostly inline), which can lead to symbol clashes.</p></li>
</ul>
<p>For example, library <code class="docutils literal notranslate"><span class="pre">A</span></code> has <code class="docutils literal notranslate"><span class="pre">class</span> <span class="pre">Q_EXPORT</span> <span class="pre">X:</span> <span class="pre">public</span> <span class="pre">QList<QVariant></span> <span class="pre">{};</span></code> and library <code class="docutils literal notranslate"><span class="pre">B</span></code> has <code class="docutils literal notranslate"><span class="pre">class</span> <span class="pre">Q_EXPORT</span> <span class="pre">Y:</span> <span class="pre">public</span> <span class="pre">QList<QVariant></span> <span class="pre">{};</span></code>.
Suddenly, <code class="docutils literal notranslate"><span class="pre">QList</span></code> symbols are exported from two libraries, which results in a clash.</p>
</li>
<li><p><strong>Aesthetics:</strong></p>
<ul class="simple">
<li><p>Put the body of a function in a <code class="docutils literal notranslate"><span class="pre">.cpp</span></code> file, not in its <code class="docutils literal notranslate"><span class="pre">.h</span></code> file.
There is a reason for having both a <code class="docutils literal notranslate"><span class="pre">.cpp</span></code> file and a <code class="docutils literal notranslate"><span class="pre">.h</span></code> file.</p></li>
<li><p>Prefer <code class="docutils literal notranslate"><span class="pre">enum</span></code> to define constants over <code class="docutils literal notranslate"><span class="pre">static</span> <span class="pre">const</span> <span class="pre">int</span></code> or <code class="docutils literal notranslate"><span class="pre">#define</span></code>.
Enumeration values will be replaced by the compiler at compile time, resulting in faster code.
Also, <code class="docutils literal notranslate"><span class="pre">#define</span></code> is not namespace safe.</p></li>
</ul>
<blockquote>
<div></div></blockquote>
</li>
</ul>
</section>
<section id="opencor-specific">
<h2>OpenCOR specific<a class="headerlink" href="#opencor-specific" title="Link to this heading">¶</a></h2>
<ul>
<li><p>Do not use <code class="docutils literal notranslate"><span class="pre">inline</span></code> functions.
It is probably better to rely on the compiler to optimise the code, if necessary, not to mention that, if badly used, <code class="docutils literal notranslate"><span class="pre">inline</span></code> functions can result in slower code.
A good resource on the topic can be found <a class="reference external" href="https://yosefk.com/c++fqa/inline.html">here</a>.</p></li>
<li><p>Divisions are costly, so replace them with multiplications wherever possible:</p>
<div class="good highlight-c++ notranslate"><div class="highlight"><pre><span></span><span class="n">a</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mf">0.5</span><span class="o">*</span><span class="n">b</span><span class="p">;</span>
</pre></div>
</div>
<div class="bad highlight-c++ notranslate"><div class="highlight"><pre><span></span><span class="n">a</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">b</span><span class="o">/</span><span class="mf">2.0</span><span class="p">;</span>
</pre></div>
</div>
</li>
<li><p>Use a reference rather than a pointer to pass a variable to a function, if you want that variable to be changed:</p>
<div class="good highlight-c++ notranslate"><div class="highlight"><pre><span></span><span class="kt">void</span><span class="w"> </span><span class="nf">function</span><span class="p">(</span><span class="kt">int</span><span class="w"> </span><span class="o">&</span><span class="n">pVar</span><span class="p">)</span>
<span class="p">{</span>
<span class="w"> </span><span class="n">pVar</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">3</span><span class="p">;</span>
<span class="p">}</span>
</pre></div>
</div>
<div class="bad highlight-c++ notranslate"><div class="highlight"><pre><span></span><span class="kt">void</span><span class="w"> </span><span class="nf">function</span><span class="p">(</span><span class="kt">int</span><span class="w"> </span><span class="o">*</span><span class="n">pVar</span><span class="p">)</span>
<span class="p">{</span>
<span class="w"> </span><span class="o">*</span><span class="n">pVar</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">3</span><span class="p">;</span>
<span class="p">}</span>
</pre></div>
</div>
</li>
<li><p>Use <code class="docutils literal notranslate"><span class="pre">qIsNull()</span></code> to test floating point numbers:</p>
<div class="good highlight-c++ notranslate"><div class="highlight"><pre><span></span><span class="w"> </span><span class="n">qIsNull</span><span class="p">(</span><span class="n">a</span><span class="o">-</span><span class="n">b</span><span class="p">)</span>
<span class="o">!</span><span class="n">qIsNull</span><span class="p">(</span><span class="n">a</span><span class="o">-</span><span class="n">b</span><span class="p">)</span>
</pre></div>
</div>
<div class="bad highlight-c++ notranslate"><div class="highlight"><pre><span></span><span class="n">a</span><span class="w"> </span><span class="o">==</span><span class="w"> </span><span class="n">b</span>
<span class="n">a</span><span class="w"> </span><span class="o">!=</span><span class="w"> </span><span class="n">b</span>
</pre></div>
</div>
</li>
<li><p>Use a constant reference to pass a variable to a function, if you do not intend to modify that variable:</p>
<div class="good highlight-c++ notranslate"><div class="highlight"><pre><span></span><span class="kt">void</span><span class="w"> </span><span class="nf">function</span><span class="p">(</span><span class="k">const</span><span class="w"> </span><span class="n">QString</span><span class="w"> </span><span class="o">&</span><span class="n">pVar</span><span class="p">)</span>
<span class="p">{</span>
<span class="w"> </span><span class="p">...</span>
<span class="p">}</span>
</pre></div>
</div>
<div class="bad highlight-c++ notranslate"><div class="highlight"><pre><span></span><span class="kt">void</span><span class="w"> </span><span class="nf">function</span><span class="p">(</span><span class="n">QString</span><span class="w"> </span><span class="n">pVar</span><span class="p">)</span>
<span class="p">{</span>
<span class="w"> </span><span class="p">...</span>
<span class="p">}</span>
</pre></div>
</div>
<p>unless it is a built-in type:</p>
<div class="good highlight-c++ notranslate"><div class="highlight"><pre><span></span><span class="kt">void</span><span class="w"> </span><span class="nf">function</span><span class="p">(</span><span class="kt">int</span><span class="w"> </span><span class="n">pVar</span><span class="p">)</span>
<span class="p">{</span>
<span class="w"> </span><span class="p">...</span>
<span class="p">}</span>
</pre></div>
</div>
<div class="bad highlight-c++ notranslate"><div class="highlight"><pre><span></span><span class="kt">void</span><span class="w"> </span><span class="nf">function</span><span class="p">(</span><span class="k">const</span><span class="w"> </span><span class="kt">int</span><span class="w"> </span><span class="o">&</span><span class="n">pVar</span><span class="p">)</span>
<span class="p">{</span>
<span class="w"> </span><span class="p">...</span>
<span class="p">}</span>
</pre></div>
</div>
</li>
</ul>
</section>
</section>
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