48 lines
1.5 KiB
C++
48 lines
1.5 KiB
C++
// Copyright (c) 2018 Robert Ramey
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//
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// Distributed under the Boost Software License, Version 1.0. (See
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// accompanying file LICENSE_1_0.txt or copy at
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// http://www.boost.org/LICENSE_1_0.txt)
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#include <iostream>
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#include <boost/safe_numerics/safe_integer.hpp>
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int main(int, const char *[]){
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std::cout << "example 3:";
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std::cout << "undetected underflow in data type" << std::endl;
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std::cout << "Not using safe numerics" << std::endl;
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// problem: decrement can yield incorrect result
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try{
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unsigned int x = 0;
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// the following silently produces an incorrect result
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--x;
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std::cout << x << " != " << -1 << std::endl;
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// when comparing int and unsigned int, C++ converts
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// the int to unsigned int so the following assertion
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// fails to detect the above error!
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assert(x == -1);
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std::cout << "error NOT detected!" << std::endl;
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}
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catch(const std::exception &){
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// never arrive here
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std::cout << "error detected!" << std::endl;
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}
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// solution: replace unsigned int with safe<unsigned int>
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std::cout << "Using safe numerics" << std::endl;
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try{
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using namespace boost::safe_numerics;
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safe<unsigned int> x = 0;
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// decrement unsigned to less than zero throws exception
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--x;
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assert(false); // never arrive here
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}
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catch(const std::exception & e){
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std::cout << e.what() << std::endl;
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std::cout << "error detected!" << std::endl;
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}
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return 0;
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}
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