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This is the documentation for a snapshot of the develop branch, built from commit 4e6c143b17.
Library Documentation Index

Safe Numerics

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Compile Time Arithmetic is Not Always Correct

If a divide by zero error occurs while a program is being compiled, there is not guarantee that it will be detected. This example shows a real example compiled with a recent version of CLang.

//  Copyright (c) 2018 Robert Ramey
//
// 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)

#include <stdexcept>
#include <iostream>

#include <boost/safe_numerics/safe_integer.hpp>

int main(int, const char *[]){
    // problem: cannot recover from arithmetic errors
    std::cout << "example 8: ";
    std::cout << "cannot detect compile time arithmetic errors" << std::endl;
    std::cout << "Not using safe numerics" << std::endl;

    try{
        const int x = 1;
        const int y = 0;
        // will emit warning at compile time
        // will leave an invalid result at runtime.
        std::cout << x / y; // will display "0"!
        std::cout << "error NOT detected!" << std::endl;
    }
    catch(const std::exception &){
        std::cout << "error detected!" << std::endl;
    }
    // solution: replace int with safe<int>
    std::cout << "Using safe numerics" << std::endl;
    try{
        using namespace boost::safe_numerics;
        const safe<int> x = 1;
        const safe<int> y = 0;
        // constexpr const safe<int> z = x / y; // note constexpr here!
        std::cout << x / y; // error would be detected at runtime
        std::cout << " error NOT detected!" << std::endl;
    }
    catch(const std::exception & e){
        std::cout << "error detected:" << e.what() << std::endl;
    }
    return 0;
}
example 8: cannot detect compile time arithmetic errors
Not using safe numerics
0error NOT detected!
Using safe numerics
error detected:positive overflow error
Program ended with exit code: 0

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