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C++ Patterns - Patterns

C++ Patterns is a repository of code patterns illustrating a modern and idiomatic approach to writing C++. The aim is to provide beginner to intermediate C++ developers a reference for solving common problems in C++. As the C++ language and library evolve, which they have been doing rapidly since the release of C++11, these patterns will be updated to match the current state-of-the-art in idiomatic C++ development.

This repository contains the source for the patterns themselves, which is used when building the C++ Patterns web front-end. For the front-end source, see sftrabbit/CppPatterns-Web.

Contributing

To contribute new patterns or edit existing ones, please fork this repository and submit pull requests for your changes. Please read the following guidelines before contributing.

TODO list

For sample ideas, please see the issues page for suggestions. If you don't feel like writing patterns yourself, feel free to add suggestions to this page.

Guidelines

What makes a good pattern?

A good pattern:

  • uses only modern C++ language and standard library features.
  • is generic and therefore widely applicable.
  • is understandable for C++ beginners.
  • acts as a starting point for learning about C++ features.

File names

Each pattern is a .cpp file that exists within a category and a section. In the repository, these files have the following path:

<category>/<section>/<pattern>.cpp

The categories are very broad and it is not expected that new categories will be added any time soon. If your pattern does not fit into an existing section, feel free to create a new section. Every category and section contains a TITLE file, giving the name of that category or section.

When the web front-end is built, numeric prefixes are stripped from category names and the section is removed. For example, the following pattern source:

1-common-tasks/classes/pimpl.cpp

is given the following page in the web front-end:

common-tasks/pimpl.html

The purpose of removing the section directory is to ensure URLs do not change when moving patterns between sections. For this reason, all pattern file names within a category must be unique.

Even if the title of a pattern changes, please avoid changing the file name. If the pattern changes significantly enough for the file name to change, then it should be a new pattern.

File format

Every pattern .cpp file must be structured as follows:

// Title
// Tag1, Tag2

Example code

// Intent paragraph
//
// Description paragraph #1
//
// Description paragraph #2

Hidden code

The title comment and tags comment must each be a single line. The tags comment is optional. The tags line should be a comma separated list of tags.

The intent and description are processed as an extended form of Markdown, which means that they support formatting such as italics, bold text, links, lists, and line references.

The example code section is displayed on the pattern page and should contain everything required to understand the pattern. The hidden code section should contain any additional code that is required in order for the file to compile and is not shown on the pattern page.

Please keep to a width of approximately 70 characters for those who might view the source without wrapping.

Markdown extensions

The pattern description is processed as a form of Markdown with the following extensions:

  1. Line references are added with the [XX-YY] syntax. The -YY is optional and used to denote a range of lines. An exclamation mark after the opening bracket causes the output to be capitalized.

    The numbers provided should denote line numbers in the original .cpp file. They will be offset automatically when building the web front-end.

    For example, [10] may expand to line 8, [10-14] may expand to lines 8-12, and [!15] may expand to Line 13 (note the capital L).

  2. To simplify links to cppreference.com, any link whose URL begins with c/ or cpp/ will automatically link to the appropriate page on cppreference.com.

Code style

The only strict requirement on code style is that it should be idiomatic and modern C++. The exact formatting of code is not too important - in fact, variations in style can be useful.

There are a few simple guidelines:

  • Avoid using auto for two reasons: firstly, the patterns are intended to be used as a reference for beginner C++ developers, and the types involved are important to help with their understanding; secondly, a consensus has not been reached on when it is appropriate to use auto.

  • Use the uniform initialisation syntax where possible.

  • Name entities with generic names (foo, bar, func, x, etc.).

  • Keep the example code as simple as possible. Give the bare minimum required to understand the pattern.

  • Do not use inline comments for explaining the pattern - that's what the pattern description should do. Use inline comments only as a placeholder for omitted code.

Writing style

The writing style for the intent and description are also not strict. However, there are a few guidelines that should be kept in mind:

  • Use the personal pronoun "we" when describing the pattern, as though you and the reader wrote this code together. It helps to make the description more personable.

  • Use line references whenever appropriate. It allows the reader cross-reference between the code and the description.

  • The intent should be a simple sentence or two describing what the purpose of the pattern is.