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C++ Cookbook
book

C++ Cookbook

by D. Ryan Stephens, Christopher Diggins, Jonathan Turkanis, Jeff Cogswell
November 2005
Beginner to intermediate content levelBeginner to intermediate
594 pages
16h 23m
English
O'Reilly Media, Inc.
Content preview from C++ Cookbook

5.6. Defining Constrained Value Types

Problem

You want self-validating numerical types to represents numbers with a limited range of valid values such as hours of a day or minutes of an hour.

Solution

When working with dates and times, frequently you will want values that are integers with a limited range of valid values (i.e., 0 to 59 for seconds of a minute, 0 to 23 for hours of a day, 0 to 365 for days of a year). Rather than checking these values every time they are passed to a function, you would probably prefer to have them validated automatically by overloading the assignment operator. Since there are so many of these types, it is preferable to implement a single type that can handle this kind of validation for different numerical ranges. Example 5-10 presents a ConstrainedValue template class implementation that makes it easy to define ranged integers and other constrained value types.

Example 5-10. constrained_value.hpp

#ifndef CONSTRAINED_VALUE_HPP #define CONSTRAINED_VALUE_HPP #include <cstdlib> #include <iostream> using namespace std; template<class Policy_T> struct ConstrainedValue { public: // public typedefs typedef typename Policy_T policy_type; typedef typename Policy_T::value_type value_type; typedef ConstrainedValue self; // default constructor ConstrainedValue() : m(Policy_T::default_value) { } ConstrainedValue(const self& x) : m(x.m) { } ConstrainedValue(const value_type& x) { Policy_T::assign(m, x); } operator value_type() const { return m; } // uses the policy ...
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Publisher Resources

ISBN: 0596007612Supplemental ContentErrata Page