Channels ▼

A Per-Thread Singleton Class

May 2002/A Per-Thread Singleton Class/Sidebar

How a Traditional Singleton Class Works

As the name indicates, the traditional Singleton class allows exactly one instance of the class to be created. The class ensures this by assuming the responsibility to regulate the creation of its objects. The class makes its constructor private, disallowing the direct creation of its objects. In addition, the class defines a static member function that must be called to get an instance of the class. The class also has a static member that stores the pointer to the sole instance of the class. A sample class is shown below:

class Singleton
static Singleton* GetObject();
static Singleton *m_Instance;

The only way to get access to an object of the class is to call the static member function GetObject. When called, GetObject first checks if an instance of the class exists, by checking if m_Instance is NULL. If m_Instance is NULL, then this function creates the first and only instance of the class Singleton, assigns it to m_Instance, and returns it. Subsequent calls to GetObject just return the value stored in m_Instance, ensuring that only one instance of the class is ever created.

Related Reading

More Insights

Currently we allow the following HTML tags in comments:

Single tags

These tags can be used alone and don't need an ending tag.

<br> Defines a single line break

<hr> Defines a horizontal line

Matching tags

These require an ending tag - e.g. <i>italic text</i>

<a> Defines an anchor

<b> Defines bold text

<big> Defines big text

<blockquote> Defines a long quotation

<caption> Defines a table caption

<cite> Defines a citation

<code> Defines computer code text

<em> Defines emphasized text

<fieldset> Defines a border around elements in a form

<h1> This is heading 1

<h2> This is heading 2

<h3> This is heading 3

<h4> This is heading 4

<h5> This is heading 5

<h6> This is heading 6

<i> Defines italic text

<p> Defines a paragraph

<pre> Defines preformatted text

<q> Defines a short quotation

<samp> Defines sample computer code text

<small> Defines small text

<span> Defines a section in a document

<s> Defines strikethrough text

<strike> Defines strikethrough text

<strong> Defines strong text

<sub> Defines subscripted text

<sup> Defines superscripted text

<u> Defines underlined text

Dr. Dobb's encourages readers to engage in spirited, healthy debate, including taking us to task. However, Dr. Dobb's moderates all comments posted to our site, and reserves the right to modify or remove any content that it determines to be derogatory, offensive, inflammatory, vulgar, irrelevant/off-topic, racist or obvious marketing or spam. Dr. Dobb's further reserves the right to disable the profile of any commenter participating in said activities.

Disqus Tips To upload an avatar photo, first complete your Disqus profile. | View the list of supported HTML tags you can use to style comments. | Please read our commenting policy.