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## Chapter 22. Boost.Ratio 2.0.0

### Howard Hinnant

### Beman Dawes

### Vicente J. Botet Escriba

Copyright © 2008 Howard Hinnant

Copyright © 2006, 2008 Beman Dawes

Copyright © 2009-2012 Vicente J. Botet Escriba

Distributed under the Boost Software License, Version 1.0. (See accompanying file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)

## Overview

#### How to Use This Documentation

This documentation makes use of the following naming and formatting conventions.

- Code is in `fixed width font` and is syntax-highlighted.
- Replaceable text that you will need to supply is in `italics`.
- Free functions are rendered in the code font followed by `()`, as in `free_function()`.
- If a name refers to a class template, it is specified like this: `class_template<>`; that is, it is in code font and its name is followed by `<>` to indicate that it is a class template.
- If a name refers to a function-like macro, it is specified like this: `MACRO()`; that is, it is uppercase in code font and its name is followed by `()` to indicate that it is a function-like macro. Object-like macros appear without the trailing `()`.
- Names that refer to concepts in the generic programming sense are specified in CamelCase.

| Note
In addition, notes such as this one specify non-essential information that provides additional background or rationale.

Finally, you can mentally add the following to any code fragments in this document:

    // Include all of Ratio files
    #include <boost/ratio.hpp>
    using namespace boost;

### Motivation

Boost.Ratio aims to implement the compile time ratio facility in C++0x, as proposed in N2661 - A Foundation to Sleep On. That document provides background and motivation for key design decisions and is the source of a good deal of information in this documentation.

### Description

The Boost.Ratio library provides:

- A class template, `ratio`, for specifying compile time rational constants such as 1/3 of a nanosecond or the number of inches per meter. `ratio` represents a compile time ratio of compile time constants with support for compile time arithmetic with overflow and division by zero protection.
- It provides a textual representation of `boost::ratio<N, D>` in the form of a `std::basic_string` which can be useful for I/O.
- Some extension related to the Rational Constant concept enabling the use of `ratio`<> in the context of Boost.MPL numeric metafunctions.

Last revised: October 29, 2012 at 22:45:27 GMT |