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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

3.6. Converting Between Numeric Types

Problem

You have number of one type and you need to convert it to another, such as an int to a short or a vice versa, but you want to catch any overflow or underflow errors at runtime.

Solution

Use Boost’s numeric_cast class template. It performs runtime checks that throw an exception of type bad_numeric_cast if you will overflow or underflow the variable where you are putting a value. Example 3-8 shows you how to do this.

Example 3-8. Safe numeric conversions

#include <iostream>
#include <boost/cast.hpp>

using namespace std;
using boost::numeric_cast;
using boost::bad_numeric_cast;

int main() {

   // Integer sizes
   try {
      int i = 32767;
      short s = numeric_cast<short>(i);

      cout << "s = " << s << endl;

      i++; // Now i is out of range (if sizeof(short) is 2)
      s = numeric_cast<short>(i);
   }
   catch (bad_numeric_cast& e) {
      cerr << e.what() << endl;
   }

   try {
      int i = 300;
      unsigned int ui = numeric_cast<unsigned int>(i);

      cout << ui << endl; // Fine

      i *= -1;
      ui = numeric_cast<unsigned int>(i); // i is negative!
   }
   catch (bad_numeric_cast& e) {
      cerr << e.what() << endl;
   }

   try {
      double d = 3.14;
      int i = numeric_cast<int>(d);

      i = numeric_cast<int>(d); // This shaves off the 0.14!

      cout << i << endl;  // i = 3

   }
   catch (bad_numeric_cast& e) {
      cerr << e.what() << endl;
   }
}

Discussion

You are probably aware of the fact that the basic C++ types have different sizes. The C++ standard has strict specifications for the relative size of types—an int is always at least as big as a

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Publisher Resources

ISBN: 0596007612Supplemental ContentErrata Page