ceph/src/boost/libs/safe_numerics/example/example3.cpp

   1 //  Copyright (c) 2018 Robert Ramey
   2 //
   3 // Distributed under the Boost Software License, Version 1.0. (See
   4 // accompanying file LICENSE_1_0.txt or copy at
   5 // http://www.boost.org/LICENSE_1_0.txt)
   6
   7 #include <iostream>
   8
   9 #include <boost/safe_numerics/safe_integer.hpp>
  10
  11 int main(int, const char *[]){
  12     std::cout << "example 3:";
  13     std::cout << "undetected underflow in data type" << std::endl;
  14     std::cout << "Not using safe numerics" << std::endl;
  15     // problem: decrement can yield incorrect result
  16     try{
  17         unsigned int x = 0;
  18         // the following silently produces an incorrect result
  19         --x;
  20         std::cout << x << " != " << -1 << std::endl;
  21
  22         // when comparing int and unsigned int, C++ converts
  23         // the int to unsigned int so the following assertion
  24         // fails to detect the above error!
  25         assert(x == -1);
  26
  27         std::cout << "error NOT detected!" << std::endl;
  28     }
  29     catch(const std::exception &){
  30         // never arrive here
  31         std::cout << "error detected!" << std::endl;
  32     }
  33     // solution: replace unsigned int with safe<unsigned int>
  34     std::cout << "Using safe numerics" << std::endl;
  35     try{
  36         using namespace boost::safe_numerics;
  37         safe<unsigned int> x = 0;
  38         // decrement unsigned to less than zero throws exception
  39         --x;
  40         assert(false); // never arrive here
  41     }
  42     catch(const std::exception & e){
  43         std::cout << e.what() << std::endl;
  44         std::cout << "error detected!" << std::endl;
  45     }
  46     return 0;
  47 }