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<TITLE>ALICE O² C++ Naming & Formatting Rules</TITLE>
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<BODY>
<H1>ALICE O² C++ Naming & Formatting Rules</H1>
<address>
Vasco Barroso<br>
Alina GrigoraȘ<br>
Ivana Hřivnáčová<br>
Matthias Kretz<br>
Adriana Telesca<br>
Barthélémy von Haller<br>
</address>
<p align="right">
This document is based on the work of <br>
B. Weinberger, C. Silverstein, <br>
G. Eitzmann, M. Mentovai <br>
and T.Landray <br>
at <a href="http://google-styleguide.googlecode.com"> http://google-styleguide.googlecode.com</a>, <br>
C++ Google Style guide, Revision 3.245 <br>
under the <a rel="license" href="http://creativecommons.org/licenses/by/3.0/deed.en_US">CC-By 3.0 License</a>
</p>
<DIV style="margin-left: 50%; font-size: 75%;">
<P>
Each style point has a summary for which additional information is available
by toggling the accompanying arrow button that looks this way:
<SPAN class="showhide_button" style="margin-left: 0; float: none">▶</SPAN>.
You may toggle all summaries with the big arrow button:
</P>
<DIV style=" font-size: larger; margin-left: +2em;">
<SPAN class="showhide_button" style="font-size: 180%; float: none" onclick="javascript:ShowHideAll()" name="show_hide_all_button" id="show_hide_all_button">▶</SPAN>
Toggle all summaries
</DIV>
</DIV>
<DIV class="toc">
<DIV class="toc_title">Table of Contents</DIV>
<TABLE>
<TR valign="top" class="">
<TD><DIV class="toc_category"><A href="#Naming">Naming</A></DIV></TD>
<TD><DIV class="toc_stylepoint">
<SPAN style="padding-right: 1em; white-space:nowrap;" class=""><A href="#General_Naming_Rules">General Naming Rules</A></SPAN> <SPAN style="padding-right: 1em; white-space:nowrap;" class=""><A href="#File_Names">File Names</A></SPAN> <SPAN style="padding-right: 1em; white-space:nowrap;" class=""><A href="#Type_Names">Type Names</A></SPAN> <SPAN style="padding-right: 1em; white-space:nowrap;" class=""><A href="#Interface_Names">Interface Names</A></SPAN> <SPAN style="padding-right: 1em; white-space:nowrap;" class=""><A href="#Variable_Names">Variable Names</A></SPAN> <SPAN style="padding-right: 1em; white-space:nowrap;" class=""><A href="#Function_Names">Function Names</A></SPAN> <SPAN style="padding-right: 1em; white-space:nowrap;" class=""><A href="#Namespace_Names">Namespace Names</A></SPAN> <SPAN style="padding-right: 1em; white-space:nowrap;" class=""><A href="#Enumerator_Names">Enumerator Names</A></SPAN> <SPAN style="padding-right: 1em; white-space:nowrap;" class=""><A href="#Macro_Names">Macro Names</A></SPAN> </DIV></TD>
</TR>
<TR valign="top" class="">
<TD><DIV class="toc_category"><A href="#Formatting">Formatting</A></DIV></TD>
<TD><DIV class="toc_stylepoint">
<SPAN style="padding-right: 1em; white-space:nowrap;" class=""><A href="#Line_Length">Line Length</A></SPAN> <SPAN style="padding-right: 1em; white-space:nowrap;" class=""><A href="#One_Statement_Per_Line">One Statement Per Line</A></SPAN> <SPAN style="padding-right: 1em; white-space:nowrap;" class=""><A href="#Spaces_vs._Tabs">Spaces vs. Tabs</A></SPAN> <SPAN style="padding-right: 1em; white-space:nowrap;" class=""><A href="#Function_Declarations_and_Definitions">Function Declarations and Definitions</A></SPAN> <SPAN style="padding-right: 1em; white-space:nowrap;" class=""><A href="#Pointer_and_Reference_Expressions">Pointer and Reference Expressions</A></SPAN> <SPAN style="padding-right: 1em; white-space:nowrap;" class=""><A href="#Boolean_Expressions">Boolean Expressions</A></SPAN> <SPAN style="padding-right: 1em; white-space:nowrap;" class=""><A href="#Variable_and_Array_Initialization">Variable and Array Initialization</A></SPAN> <SPAN style="padding-right: 1em; white-space:nowrap;" class=""><A href="#Preprocessor_Directives">Preprocessor Directives</A></SPAN> <SPAN style="padding-right: 1em; white-space:nowrap;" class=""><A href="#Classes">Classes</A></SPAN> <SPAN style="padding-right: 1em; white-space:nowrap;" class=""><A href="#Constructor_Initializer_Lists">Constructor Initializer Lists</A></SPAN> <SPAN style="padding-right: 1em; white-space:nowrap;" class=""><A href="#Namespaces">Namespaces</A></SPAN> <SPAN style="padding-right: 1em; white-space:nowrap;" class=""><A href="#Braces">Braces</A></SPAN> <SPAN style="padding-right: 1em; white-space:nowrap;" class=""><A href="#Horizontal_Whitespace">Horizontal Whitespace</A></SPAN> <SPAN style="padding-right: 1em; white-space:nowrap;" class=""><A href="#Vertical_Whitespace">Vertical Whitespace</A></SPAN> <SPAN style="padding-right: 1em; white-space:nowrap;" class=""><A href="#Where_to_put_const">Where to put const</A></SPAN> </DIV></TD>
</TR>
<TR valign="top" class="">
<TD><DIV class="toc_category"><A href="#Exceptions_to_the_Rules">Exceptions to the Rules</A></DIV></TD>
<TD><DIV class="toc_stylepoint">
<SPAN style="padding-right: 1em; white-space:nowrap;" class=""><A href="#Existing_Non-conformant_Code">Existing Non-conformant Code</A></SPAN> </DIV></TD>
</TR>
</TABLE>
</DIV>
<DIV class="">
<H2 name="Background" id="Background">Background</H2>
<p>
The goal of this guide is to provide a number of rules that keep the code base manageable by enforcing
<em>consistency</em>.
It is very important that any programmer
can look at another programmer's code and understand it quickly.
Maintaining a uniform style and following conventions means that "pattern-matching" can be
more easily used to identify different symbols and invariants.
</p>
<p>
Creating common, required
idioms and patterns makes code much easier to understand. In some
cases there might be good arguments for changing certain style
rules. Nonetheless, for reasons of consistency the rules are left unchanged.
</p>
<p>
Note that this guide is not a C++ tutorial: we assume that the
reader is familiar with the language.
</p>
</DIV>
<DIV class="">
<H2 name="Naming" id="Naming">Naming</H2>
<p>
The most important consistency rules are those that govern
naming. The style of a name immediately informs us what sort of
thing the named entity is: a type, a variable, a function, a macro, etc., without requiring us to search for the
declaration of that entity. The pattern-matching engine in our
brains relies a great deal on these naming rules.
</p>
<p>
Naming rules are pretty arbitrary, but we feel that consistency is more important than individual preferences in this area, so regardless of whether you find them sensible or not, the rules are the rules.
</p>
<DIV class="">
<H3><A name="General_Naming_Rules" id="General_Naming_Rules">General Naming Rules</A></H3>
<SPAN class="link_button" id="link-General_Naming_Rules__button" name="link-General_Naming_Rules__button"><A href="?showone=General_Naming_Rules#General_Naming_Rules">
link
</A></SPAN><SPAN class="showhide_button" onclick="javascript:ShowHideByName('General_Naming_Rules')" name="General_Naming_Rules__button" id="General_Naming_Rules__button">▶</SPAN>
<DIV style="display:inline;" class="">
Names should be meaningful; abbreviations should be avoided.
They follow camel case convention. Types and variables should be nouns,
while functions should be "command" verbs. </DIV>
<DIV class=""><DIV class="stylepoint_body" name="General_Naming_Rules__body" id="General_Naming_Rules__body" style="display: none">
<P class="">
<SPAN class="stylepoint_subsection">How to Name</SPAN>
<p>
Within reason, give as descriptive a name as possible. Do
not worry about saving horizontal space as it is far more
important to make your code immediately understandable to a
new reader. Examples of well-chosen names:
</p>
<DIV class=""><PRE>int numberOfErrors; // Good.
int numberOfCompletedConnections; // Good.</PRE></DIV>
<p>
Poorly chosen names use ambiguous abbreviations or arbitrary
characters that do not convey meaning.
Do not use directly the variable names from mathematical formulas.
In mathematics, variable names are usually limited to a single letter.
To implement a mathematical formula use variable names that
clearly indicate what value it holds.
</p>
<DIV class=""><PRE>float distance = velocity * time; // Good - no ambiguity</PRE></DIV>
<DIV class=""><PRE class="badcode">int n; // Bad - meaningless.
int nerr; // Bad - ambiguous abbreviation.
int nCompConns; // Bad - ambiguous abbreviation.
float s = v * t; // Bad - almost meaningless.</PRE></DIV>
<p>
Type and variable names should typically be nouns: e.g.,
<code>FileOpener</code>, <code>numberOfErrors</code>.
</p>
<p>
Function names should typically be imperative (that is they
should be commands): e.g., <code>openFile()</code>,
<code>setNumberOfErrors()</code>.
</p>
</P>
<P class="">
<SPAN class="stylepoint_subsection">CamelCase Convention</SPAN>
<p>
All names in C++ code follow camel case convention. This is
the practice of writing compound words so that each word
begins with a capital letter. No underscores are allowed.
</p>
<p>
For example:
</p>
<DIV class=""><PRE>string tableName; // Good</PRE></DIV>
<DIV class=""><PRE class="badcode">string table_name; // Bad - uses underscore.
string tablename; // Bad - all lowercase.</PRE></DIV>
</P>
<P class="">
<SPAN class="stylepoint_subsection">Capitalization Rules</SPAN>
<p>
Variables and functions start with a lowercase letter.<br>
Everything else in C++ code (namespaces, type names, constant
expressions) starts with an uppercase letter.
</p>
</P>
<P class="">
<SPAN class="stylepoint_subsection">Abbreviations</SPAN>
<p>
Do not use abbreviations except for acronyms. For example:
</p>
<DIV class=""><PRE>// Good. These show proper names with no abbreviations.
int numberOfDnsConnections; // Most people know what "DNS" stands for.
int priceCount; // Price count, it makes sense.
int daqRate; // In ALICE everyone knows what DAQ stands for.</PRE></DIV>
<DIV class=""><PRE class="badcode">// Bad. Abbreviations can be confusing or ambiguous outside a small group.
int wgcConnections; // Only your group knows what this stands for.
int pcReader; // Lots of things can be abbreviated "pc".</PRE></DIV>
<p>
A single letter variable name can be used for well-known idioms like iterators of integer type and pimpl-idioms (d-pointer).
</p>
<DIV class=""><PRE>for (int i = 0 ; i < 10 ; i++) { // Good.
prices[i] = 0;
}</PRE></DIV>
<DIV class=""><PRE class="badcode">for (auto i = &prices[0]; i < &prices[10]; ++i) { // Bad
*i = 0; // i is not of integer type
}</PRE></DIV>
<p>
Never abbreviate by leaving out letters. <br>
Exception:
You may use <code>it</code> for iterator names or their names prefix.
</p>
<DIV class=""><PRE>// Good
std::vector<int > myVector;
auto it = myVector.begin();
auto itMyVector = myVector.begin();
auto myVectorIterator = myVector.begin(); </PRE></DIV>
<DIV class=""><PRE class="badcode">auto myVectorIt = myVector.begin(); // Bad. It is abbreviated, but not a prefix.</PRE></DIV>
</P>
</DIV></DIV>
</DIV>
<DIV class="">
<H3><A name="File_Names" id="File_Names">File Names</A></H3>
<SPAN class="link_button" id="link-File_Names__button" name="link-File_Names__button"><A href="?showone=File_Names#File_Names">
link
</A></SPAN><SPAN class="showhide_button" onclick="javascript:ShowHideByName('File_Names')" name="File_Names__button" id="File_Names__button">▶</SPAN>
<p> </p>
<DIV style="display:inline;" class="">
C++ code file names are derived from the class (or the namespace)
names. <br>
Program file names and utility file names, which do not define a class
or a namespace, start with a lower case letter.<br>
</DIV>
<DIV class=""><DIV class="stylepoint_body" name="File_Names__body" id="File_Names__body" style="display: none">
<p>
C++ implementation files should end in <code>.cxx</code> and header files
should end in <code>.h</code>.
</p>
<p>
Inline functions should go directly into your
<code>.h</code> file. However, if they include a lot of code, they may go into a third file that
ends in <code>.inl</code>. This rule applies to templates too.
</p>
<p>
Do not use filenames that already exist
in <code>/usr/include</code>, such as <code>db.h</code>.
</p>
<p>
Examples of acceptable file names:
</p>
<DIV class=""><PRE>MyClass.h // The class declaration.
MyClass.cxx // The class definition.
MyClass.inl // Inline functions that include lots of code.
myUtilities.h // Utility functions/definitions
testMyClass.cxx // Test program</PRE></DIV>
<p>
Having upper case letters in a file name might theoretically lead to problems for case-insensitive operating systems.
However, as the file name corresponds to the class name it seems important to keep the same case as well.
Moreover, having two valid class/file names that would collide on a not-case sensitive OS seems extremely unlikely.
</p>
</DIV></DIV>
</DIV>
<DIV class="">
<H3><A name="Type_Names" id="Type_Names">Type Names</A></H3>
<SPAN class="link_button" id="link-Type_Names__button" name="link-Type_Names__button"><A href="?showone=Type_Names#Type_Names">
link
</A></SPAN><SPAN class="showhide_button" onclick="javascript:ShowHideByName('Type_Names')" name="Type_Names__button" id="Type_Names__button">▶</SPAN>
<DIV style="display:inline;" class="">
Type names follow camel case convention and start with an upper case letter:
<code>MyClass</code>, <code>MyEnum</code>.
</DIV>
<DIV class=""><DIV class="stylepoint_body" name="Type_Names__body" id="Type_Names__body" style="display: none">
<p>
The names of all types — classes, structs, typedefs, and enums
— have the same naming convention. For example:
</p>
<DIV class=""><PRE>// classes and structs
class UrlTable
{ ...
class UrlTableTester
{ ...
struct UrlTableProperties
{ ...
// typedefs
typedef HashMap<UrlTableProperties *, string> PropertiesMap;
// enums
enum UrlTableErrors { ...</PRE></DIV>
</DIV></DIV>
</DIV>
<DIV class="">
<H3><A name="Interface_Names" id="Interface_Names">Interface Names</A></H3>
<SPAN class="link_button" id="link-Interface_Names__button" name="link-Interface_Names__button"><A href="?showone=Interface_Names#Interface_Names">
link
</A></SPAN><SPAN class="showhide_button" onclick="javascript:ShowHideByName('Interface_Names')" name="Interface_Names__button" id="Interface_Names__button">▶</SPAN>
<DIV style="display:inline;" class="">
The "Interface" suffix can optionally be used only if a class matches the <I><a href="https://htmlpreview.github.io/?https://github.com/AliceO2Group/CodingGuidelines/blob/master/coding_guidelines.html#Interfaces">Pure Interface</a></I> requirements.
</DIV>
<DIV class=""><DIV class="stylepoint_body" name="Interface_Names__body" id="Interface_Names__body" style="display: none">
<DIV class=""><PRE>// pure interface
class UrlTableInterface
{ ...</PRE></DIV>
</DIV></DIV>
</DIV>
<DIV class="">
<H3><A name="Variable_Names" id="Variable_Names">Variable Names</A></H3>
<SPAN class="link_button" id="link-Variable_Names__button" name="link-Variable_Names__button"><A href="?showone=Variable_Names#Variable_Names">
link
</A></SPAN><SPAN class="showhide_button" onclick="javascript:ShowHideByName('Variable_Names')" name="Variable_Names__button" id="Variable_Names__button">▶</SPAN>
<DIV style="display:inline;" class="">
Variable names follow camel case convention and start with
a lower case letter: <code>myLocalVariable</code>.
<ul>
<li>Class member variables are prefixed with <code>m</code>.</li>
<li>Static class member variables are prefixed with <code>s</code>.</li>
<li>No <code>m</code> prefix for struct members.</li>
<li>Global variables are prefixed with <code>g</code>.</li>
<li>
<code>constexpr</code> variables are capitalized.</li>
<li>No additional prefix for <code>const</code>.</li>
</ul>
</DIV>
<DIV class=""><DIV class="stylepoint_body" name="Variable_Names__body" id="Variable_Names__body" style="display: none">
<P class="">
<SPAN class="stylepoint_subsection">Local Variable names</SPAN>
<p>
For example:
</p>
<DIV class=""><PRE>string tableName; // Good.</PRE></DIV>
</P>
<P class="">
<SPAN class="stylepoint_subsection">Class Data Members</SPAN>
<p>
Data members (also called instance variables or member
variables) are prefixed with <code>m</code>.
If the data member is <code>static</code>, prefix the variable with <code>s</code> instead.
</p>
<DIV class=""><PRE>class Something
{
private:
string mTableName;
static int sGlobalState;
};</PRE></DIV>
</P>
<P class="">
<SPAN class="stylepoint_subsection">Struct Variables</SPAN>
<p>
Data members in structs are named like regular
variables.
</p>
<DIV class=""><PRE>struct UrlTableProperties
{
string name;
int numberOfEntries;
}</PRE></DIV>
</P>
<P class="">
<SPAN class="stylepoint_subsection">Global Variables</SPAN>
<p>
Global variables,
which should be rare in any case, are prefixed with <code>g</code>.
</p>
</P>
<P class="">
<SPAN class="stylepoint_subsection">constexpr</SPAN>
<p>
A variable declared as <code>constexpr</code> typically is only used as compile-time constant (but may be stored in read-only memory).
Therefore it uses the same convention as <code>enum</code>s and uses uppercase CamelCase.
</p>
<DIV class=""><PRE>constexpr double LightSpeed = 2.99792458e+8;</PRE></DIV>
</P>
<P class="">
<SPAN class="stylepoint_subsection">const</SPAN>
<p>
A variable declared as <code>const</code> does not have any additional naming rules.
The prefixes describe the scope of the variable.
<code>const</code> is just one aspect of the type of the variable.
</p>
<p>
To provide a constant in the public interface consider <code>constexpr</code>,
<code>enum</code>, or a (<code>constexpr</code>) function instead.
</p>
</P>
</DIV></DIV>
</DIV>
<DIV class="">
<H3><A name="Function_Names" id="Function_Names">Function Names</A></H3>
<SPAN class="link_button" id="link-Function_Names__button" name="link-Function_Names__button"><A href="?showone=Function_Names#Function_Names">
link
</A></SPAN><SPAN class="showhide_button" onclick="javascript:ShowHideByName('Function_Names')" name="Function_Names__button" id="Function_Names__button">▶</SPAN>
<DIV style="display:inline;" class="">
Regular functions follow camel case convention and start with a lower case
letter: <code>myFunction()</code>.
<ul>
<li>Accessors and mutators match the name of the variable and are
prefixed with <code>get</code> and <code>set</code>:
<code>getMyMemberVariable()</code>, <code>setMyMemberVariable()</code>.</li>
<li> Functions (including accessors) returning a boolean value should be prefixed with
<code>is</code> or <code>has</code>. </li>
</ul>
</DIV>
<DIV class=""><DIV class="stylepoint_body" name="Function_Names__body" id="Function_Names__body" style="display: none">
<P class="">
<SPAN class="stylepoint_subsection">Regular Functions</SPAN>
<p>
Example of functions:
</p>
<DIV class=""><PRE>addTableEntry();
deleteUrl();</PRE></DIV>
<p>
The rule applies also to <code>constexpr</code> functions:
</p>
<DIV class=""><PRE>constexpr int getFive() { return 5; } </PRE></DIV>
</P>
<P class="">
<SPAN class="stylepoint_subsection">Accessors and Mutators</SPAN>
<p>
Accessors and mutators match
the name of the variable they are getting and setting and use
the prefixes <code>get</code> and <code>set</code>. The prefixes
<code>get</code> and <code>set</code> are not exclusive for accessors and mutators and they could
be used for other functions, if applicable.
This shows an excerpt of a class whose instance variable is
<code>mNumberOfEntries</code>:
</p>
<DIV class=""><PRE>class MyClass
{
public:
...
int getNumberOfEntries() const { return mNumberOfEntries; }
void setNumberOfEntries(int numberOfEntries) { mNumberOfEntries = numEntries; }
private:
int mNumberOfEntries;
};</PRE></DIV>
</P>
<P class="">
<SPAN class="stylepoint_subsection">Functions returning a boolean value</SPAN>
<p>
Functions returning a boolean value should be prefixed with
<code>is</code> or <code>has</code>:
</p>
<DIV class=""><PRE>bool isOpen();
bool hasZero();</PRE></DIV>
<p> This rule applies also to class member functions where <code>is</code> or <code>has</code> replace <code>get</code>:
</p>
<DIV class=""><PRE>class MyClass
{
public:
void setValid(bool isValid) const { mValid = isValid; }
bool isValid() const { return mValid; }
private:
bool mValid;
};</PRE></DIV>
</P>
</DIV></DIV>
</DIV>
<DIV class="">
<H3><A name="Namespace_Names" id="Namespace_Names">Namespace Names</A></H3>
<SPAN class="link_button" id="link-Namespace_Names__button" name="link-Namespace_Names__button"><A href="?showone=Namespace_Names#Namespace_Names">
link
</A></SPAN><SPAN class="showhide_button" onclick="javascript:ShowHideByName('Namespace_Names')" name="Namespace_Names__button" id="Namespace_Names__button">▶</SPAN>
<DIV style="display:inline;" class="">
Namespace names follow underscore convention and start with a lower case
letter: <code>my_namespace</code>.
</DIV>
<DIV class=""><DIV class="stylepoint_body" name="Namespace_Names__body" id="Namespace_Names__body" style="display: none">
<DIV class=""><PRE>namespace my_namespace
{
void MyClass::doSomething()
{
...
}
}</PRE></DIV>
</DIV></DIV>
</DIV>
<DIV class="">
<H3><A name="Enumerator_Names" id="Enumerator_Names">Enumerator Names</A></H3>
<SPAN class="link_button" id="link-Enumerator_Names__button" name="link-Enumerator_Names__button"><A href="?showone=Enumerator_Names#Enumerator_Names">
link
</A></SPAN><SPAN class="showhide_button" onclick="javascript:ShowHideByName('Enumerator_Names')" name="Enumerator_Names__button" id="Enumerator_Names__button">▶</SPAN>
<DIV style="display:inline;" class="">
Enumerations and enumerators (the type and the values) follow camel case
convention and start with an upper case letter:
<code> MyEnumType</code>, <code>MyEnumValue</code>.
<ul>
<li>Enumerators in unscoped enumerations should have a common
prefix/postfix derived from the enumerations name. </li>
<li>Enum classes are already scoped and therefore the enumerators do not
need a prefix/postfix.</li>
</ul>
</DIV>
<DIV class=""><DIV class="stylepoint_body" name="Enumerator_Names__body" id="Enumerator_Names__body" style="display: none">
<P class="">
<SPAN class="stylepoint_section">Definition: </SPAN>
A <i>scoped</i> enum is one that is declared with the <code>class</code>
keyword, as opposed to a <i>traditional</i> enum, which is unscoped and
doesn't include the <code>class</code> keyword in its declaration.
</P>
<p>
Unscoped enumerators are exposed to the enclosing scope.
Therefore they should be prefixed or postfixed (decided by which position makes the code more prose-like)
with the enumeration's name (or a sensible part thereof).
All names use uppercase CamelCase.
</p>
<p>
Example of an unscoped enumeration:
</p>
<DIV class=""><PRE>enum Something {
SomethingSmall, // the type name as prefix
SomethingBig,
SomethingElse
};
void add(Something);
...
add(SomethingSmall);
add(SomethingElse);</PRE></DIV>
<p>
Another example of an unscoped enumeration whose enumerators are prefixed with just a (sensible) part
of the type name.
</p>
<DIV class=""><PRE>enum MallocAlignment {
AlignOnVector, // the "Align" prefix taken from the type name
AlignOnCacheline,
AlignOnPage
}
template<MallocAlignment A> void* malloc(size_t);
...
void* memory = malloc<AlignOnCacheline>(64);</PRE></DIV>
<p>
Enum classes (new in C++11) create scoped enumerators.
Therefore there is no need for prefixing or postfixing.
</p>
<DIV class=""><PRE>enum class Something : int {
Small,
Big,
Unknown
};
void add(Something);
...
add(Something::Small);
add(Something::Unknown);</PRE></DIV>
The following enum is forbidden unless it is enclosed in a private namespace.
The names <code>Ok</code> and <code>OutOfMemory</code> are too generic to be added to the global namespace.
<DIV class=""><PRE class="badcode">enum UrlTableErrors {
Ok, // Bad.
OutOfMemory // Bad.
};</PRE></DIV>
</DIV></DIV>
</DIV>
<DIV class="">
<H3><A name="Macro_Names" id="Macro_Names">Macro Names</A></H3>
<SPAN class="link_button" id="link-Macro_Names__button" name="link-Macro_Names__button"><A href="?showone=Macro_Names#Macro_Names">
link
</A></SPAN><SPAN class="showhide_button" onclick="javascript:ShowHideByName('Macro_Names')" name="Macro_Names__button" id="Macro_Names__button">▶</SPAN>
<DIV style="display:inline;" class="">
All uppercase letters and underscores, prefixed with the sub/project name, i.e. <code>MY_PROJECT_PKG1_MY_MACRO</code>.
</DIV>
<DIV class=""><DIV class="stylepoint_body" name="Macro_Names__body" id="Macro_Names__body" style="display: none">
<p>
For the rules on Macro usage see <a href="#Preprocessor_Macros">here</a>.
</p>
<p>
They must be named with all uppercase letters and underscores, prefixed with the
sub/project name.
</p>
<DIV class=""><PRE>#define O2_VERTEX_ROUND(x) ...
#define O2_CORE_PI_ROUNDED 3.0</PRE></DIV>
Be sure to never put an underscore as prefix nor use a double underscore.
First it doesn't follow our naming convention.
Second, and more importantly, it is reserved to compiler developers.
<DIV class=""><PRE class="badcode">#define _WRONG
#define WRONG__AGAIN
</PRE></DIV>
</DIV></DIV>
</DIV>
</DIV>
<DIV class="">
<H2 name="Formatting" id="Formatting">Formatting</H2>
<p>
Coding style and formatting are pretty arbitrary. However, a good project
is much easier to follow if everyone uses the same style. Individuals
may not agree with every aspect of the formatting rules, and some of
the rules may be hard to get used to. Even so, it is important that all
project contributors
follow the style rules so that
they
can all read and understand everyone's code easily.
</p>
<DIV class="">
<H3><A name="Line_Length" id="Line_Length">Line Length</A></H3>
<SPAN class="link_button" id="link-Line_Length__button" name="link-Line_Length__button"><A href="?showone=Line_Length#Line_Length">
link
</A></SPAN><SPAN class="showhide_button" onclick="javascript:ShowHideByName('Line_Length')" name="Line_Length__button" id="Line_Length__button">▶</SPAN>
<DIV style="display:inline;" class="">
Each line of text in your code should be at most 120 characters
long.
</DIV>
<DIV class=""><DIV class="stylepoint_body" name="Line_Length__body" id="Line_Length__body" style="display: none">
<p>
Try keeping lines below 120 characters.
In some cases it may make sense to use much longer lines (e.g. for block editing).
But this should be confined to special sections in the code.
</p>
</DIV></DIV>
</DIV>
<DIV class="">
<H3><A name="One_Statement_Per_Line" id="One_Statement_Per_Line">One Statement Per Line</A></H3>
<SPAN class="link_button" id="link-One_Statement_Per_Line__button" name="link-One_Statement_Per_Line__button"><A href="?showone=One_Statement_Per_Line#One_Statement_Per_Line">
link
</A></SPAN><SPAN class="showhide_button" onclick="javascript:ShowHideByName('One_Statement_Per_Line')" name="One_Statement_Per_Line__button" id="One_Statement_Per_Line__button">▶</SPAN>
<DIV style="display:inline;" class="">
Prefer one statement per line because it improves code readability.
</DIV>
<DIV class=""><DIV class="stylepoint_body" name="One_Statement_Per_Line__body" id="One_Statement_Per_Line__body" style="display: none">
<DIV class=""><PRE>// Good. One statement per line.
if (condition) {
doSomething();
}
else {
doAnotherThing;
}</PRE></DIV>
<DIV class=""><PRE class="badcode">// Bad. Two statements per line.
if (condition) doSomething(); else doAnotherThing; </PRE></DIV>
</DIV></DIV>
</DIV>
<DIV class="">
<H3><A name="Spaces_vs._Tabs" id="Spaces_vs._Tabs">Spaces vs. Tabs</A></H3>
<SPAN class="link_button" id="link-Spaces_vs._Tabs__button" name="link-Spaces_vs._Tabs__button"><A href="?showone=Spaces_vs._Tabs#Spaces_vs._Tabs">
link
</A></SPAN><SPAN class="showhide_button" onclick="javascript:ShowHideByName('Spaces_vs._Tabs')" name="Spaces_vs._Tabs__button" id="Spaces_vs._Tabs__button">▶</SPAN>
<DIV style="display:inline;" class="">
Indent with 2 spaces. Use only spaces, no tabs.
</DIV>
<DIV class=""><DIV class="stylepoint_body" name="Spaces_vs._Tabs__body" id="Spaces_vs._Tabs__body" style="display: none">
<p>
Spaces are used for indentation. Do not use tabs in your code.
You should set your editor to emit spaces when you hit the tab
key.
</p>
</DIV></DIV>
</DIV>
<DIV class="">
<H3><A name="Function_Declarations_and_Definitions" id="Function_Declarations_and_Definitions">Function Declarations and Definitions</A></H3>
<SPAN class="link_button" id="link-Function_Declarations_and_Definitions__button" name="link-Function_Declarations_and_Definitions__button"><A href="?showone=Function_Declarations_and_Definitions#Function_Declarations_and_Definitions">
link
</A></SPAN><SPAN class="showhide_button" onclick="javascript:ShowHideByName('Function_Declarations_and_Definitions')" name="Function_Declarations_and_Definitions__button" id="Function_Declarations_and_Definitions__button">▶</SPAN>
<DIV style="display:inline;" class="">
A function declaration is on one line if possible. Otherwise the parameters that do not
fit are on the next line(s).
</DIV>
<DIV class=""><DIV class="stylepoint_body" name="Function_Declarations_and_Definitions__body" id="Function_Declarations_and_Definitions__body" style="display: none">
<p>
The return type, function name and open parenthesis are always on the same line.
The open curly brace is at the beginning of the new line after the last parameter
except for inline functions.
</p>
<p>
Example:
</p>
<DIV class=""><PRE>ReturnType ClassName::functionName(Type parName1, Type parName2)
{
doSomething();
...
}</PRE></DIV>
<p>
Example of an inline function on one line:
</p>
<DIV class=""><PRE>inline int getValue() const { return mValue; }</PRE></DIV>
</DIV></DIV>
</DIV>
<DIV class="">
<H3><A name="Pointer_and_Reference_Expressions" id="Pointer_and_Reference_Expressions">Pointer and Reference Expressions</A></H3>
<SPAN class="link_button" id="link-Pointer_and_Reference_Expressions__button" name="link-Pointer_and_Reference_Expressions__button"><A href="?showone=Pointer_and_Reference_Expressions#Pointer_and_Reference_Expressions">
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</A></SPAN><SPAN class="showhide_button" onclick="javascript:ShowHideByName('Pointer_and_Reference_Expressions')" name="Pointer_and_Reference_Expressions__button" id="Pointer_and_Reference_Expressions__button">▶</SPAN>
<DIV style="display:inline;" class="">
No spaces around period or arrow. Pointer operators are either followed
or preceded with a space.
</DIV>
<DIV class=""><DIV class="stylepoint_body" name="Pointer_and_Reference_Expressions__body" id="Pointer_and_Reference_Expressions__body" style="display: none">
<p>
The following are examples of correctly formatted pointer and
reference expressions:
</p>
<DIV class=""><PRE>int value = *valuePointer;
int* valuePointer = &value;
int value = myObject->getValue();
int value = myStruct.value;</PRE></DIV>
<p>
When declaring a pointer or reference, the `*` or `&` goes with the type.
</p>
<DIV class=""><PRE>
// Pointers
char* myCharacter; // typical C++ notation
// References
const string& myString;</PRE></DIV>
<DIV class=""><PRE class="badcode">char * myCharacter; // Bad - spaces on both sides of *
char *myCharacter; // Bad - space before the *, the * is with the variable name.
const string &myString; // Bad - the & is with the variable name.
const string & myString; // Bad - spaces on both sides of &</PRE></DIV>
</DIV></DIV>
</DIV>
<DIV class="">
<H3><A name="Boolean_Expressions" id="Boolean_Expressions">Boolean Expressions</A></H3>
<SPAN class="link_button" id="link-Boolean_Expressions__button" name="link-Boolean_Expressions__button"><A href="?showone=Boolean_Expressions#Boolean_Expressions">
link
</A></SPAN><SPAN class="showhide_button" onclick="javascript:ShowHideByName('Boolean_Expressions')" name="Boolean_Expressions__button" id="Boolean_Expressions__button">▶</SPAN>
<DIV style="display:inline;" class="">
In the case of a boolean expression that is longer than the <a href="#Line_Length">standard line length</a>, lines should be broken up in a consistent way. All operators should be either at the beginning or at the end of the line.
</DIV>
<DIV class=""><DIV class="stylepoint_body" name="Boolean_Expressions__body" id="Boolean_Expressions__body" style="display: none">
<p>
In this example, the logical AND operator is always at the end
of the lines:
</p>
<DIV class=""><PRE>if (thisOneThing > thisOtherThing &&
aThirdThing == aFourthThing &&
yetAnother && lastOne) {
...
}</PRE></DIV>
</DIV></DIV>
</DIV>
<DIV class="">
<H3><A name="Variable_and_Array_Initialization" id="Variable_and_Array_Initialization">Variable and Array Initialization</A></H3>
<SPAN class="link_button" id="link-Variable_and_Array_Initialization__button" name="link-Variable_and_Array_Initialization__button"><A href="?showone=Variable_and_Array_Initialization#Variable_and_Array_Initialization">
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</A></SPAN><SPAN class="showhide_button" onclick="javascript:ShowHideByName('Variable_and_Array_Initialization')" name="Variable_and_Array_Initialization__button" id="Variable_and_Array_Initialization__button">▶</SPAN>
<DIV style="display:inline;" class="">
Prefer initialization with braces except for single-argument assignment.
</DIV>
<DIV class=""><DIV class="stylepoint_body" name="Variable_and_Array_Initialization__body" id="Variable_and_Array_Initialization__body" style="display: none">
<p>
Example of single-argument assignments:
</p>
<DIV class=""><PRE>int x = 3; // preferred style
std::string name = "Some Name";
int x { 3 }; // also possible
std::string name{ "Some Name" };
std::string name = { "Some Name" };</PRE></DIV>
<p>
Using <code>{}</code> for initialization is more consistent, more correct, and avoids
having to know about old-style pitfalls [1].
</p>
<p>
Example of variable initialization:
</p>
<DIV class=""><PRE>Rectangle window{ 0, 0, 1024, 768 }; // preferred style
Rectangle window = { 0, 0, 1024, 768 }; // also possible
Rectangle window(0, 0, 1024, 768); // avoid unless necessary</PRE></DIV>
<p>
There is one exception: In rare cases a class may provide an <code>std::initializer_list</code> constructor and other constructors that are hidden by the <code>std::initializer_list</code> constructor.
The hidden constructor can then still be accessed with <code>()</code>.
</p>
<DIV class=""><PRE>std::vector<int> v( 10, 20 ); // calls vector(size_t n, const int &value)
std::vector<int> v{ 10, 20 }; // calls vector(std::initializer_list<int> values)</PRE></DIV>
</DIV></DIV>
</DIV>
<DIV class="">
<H3><A name="Preprocessor_Directives" id="Preprocessor_Directives">Preprocessor Directives</A></H3>
<SPAN class="link_button" id="link-Preprocessor_Directives__button" name="link-Preprocessor_Directives__button"><A href="?showone=Preprocessor_Directives#Preprocessor_Directives">
link
</A></SPAN><SPAN class="showhide_button" onclick="javascript:ShowHideByName('Preprocessor_Directives')" name="Preprocessor_Directives__button" id="Preprocessor_Directives__button">▶</SPAN>
<DIV style="display:inline;" class="">
The hash mark that starts a preprocessor directive is
always at the beginning of the line.
</DIV>
<DIV class=""><DIV class="stylepoint_body" name="Preprocessor_Directives__body" id="Preprocessor_Directives__body" style="display: none">
<p>
Even when preprocessor directives are within the body of
indented code, the directives should start at the beginning of
the line.
</p>
<DIV class=""><PRE>// Good - directives at beginning of line
if (lopsidedScore) {
#if DISASTER_PENDING
dropEverything();
# if NOTIFY // Good but not required -- Spaces after #
notifyClient();
# endif
#endif
goBackToNormal();
}</PRE></DIV>
<DIV class=""><PRE class="badcode">// Bad - indented directives
if (lopsidedScore) {
#if DISASTER_PENDING // The "#if" should be at beginning of line
dropEverything();
#endif // Do not indent "#endif"
goBackToNormal();
}</PRE></DIV>
</DIV></DIV>
</DIV>
<DIV class="">
<H3><A name="Classes" id="Classes">Classes</A></H3>
<SPAN class="link_button" id="link-Classes__button" name="link-Classes__button"><A href="?showone=Classes#Classes">
link
</A></SPAN><SPAN class="showhide_button" onclick="javascript:ShowHideByName('Classes')" name="Classes__button" id="Classes__button">▶</SPAN>
<DIV style="display:inline;" class="">
Access specifiers in a class or a struct are indented by 1 space.
The sections they delimit are themselves indented by 1 more space for a total of 2 spaces.
</DIV>
<DIV class=""><DIV class="stylepoint_body" name="Classes__body" id="Classes__body" style="display: none">
<p>
The basic format for a class declaration is:
</p>
<DIV class=""><PRE>class MyClass : public BaseClass
{
public: // 1 spaces indent.
MyClass(); // 2 spaces indent.
~MyClass() {}
void someFunction();
void someFunctionThatDoesNothing() {}
void setSomeValue(int value) { mSomeValue = value; }
private:
bool someInternalFunction(); // notice that the method is before the data members
int mSomeValue;
int mSomeOtherValue;
};</PRE></DIV>
<p>
Things to note:
</p>
<ul>
<li> The base class name should be on the same line as the
subclass name, subject to the 120-character limit.
</li>
<li> Except for the first instance, the access specifier keywords should be preceded
by a blank line. This rule is optional for small classes.
</li>
<li> Do not leave a blank line after access specifier keywords.
</li>
<li> The <code>public</code> section should be first, followed by
the <code>protected</code> and finally the
<code>private</code> section.
</li>
<li> Generally, each access specifier appears only once in a class
declaration. </li>
<li>
Within each section, the declarations should be in the following order:
<ul>
<li> Constructors</li>
<li> Destructor</li>
<li> Methods</li>
<li> Data Members </li>
</ul>
</li>
</ul>
In certain situations you might need to use a different declaration order. For example, when using <code>decltype</code> :
<DIV class=""><PRE>class A
{
private: // Early declaration of a private data member
int x;