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81 lines
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81 lines
3.7 KiB
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<title>Array index value can exceed array limits</title>
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<td><h2>Safe Numerics</h2></td>
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<a accesskey="p" href="4.html"><img src="../images/prev.png" alt="Prev"></a><a accesskey="u" href="../tutorial.html"><img src="../images/up.png" alt="Up"></a><a accesskey="h" href="../index.html"><img src="../images/home.png" alt="Home"></a><a accesskey="n" href="6.html"><img src="../images/next.png" alt="Next"></a>
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<div class="titlepage"><div><div><h3 class="title">
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<a name="safe_numerics.tutorial.5"></a>Array index value can exceed array limits</h3></div></div></div>
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<p>Using an intrinsic C++ array, it's very easy to exceed array limits.
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This can fail to be detected when it occurs and create bugs which are hard
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to find. There are several ways to address this, but one of the simplest
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would be to use safe_unsigned_range;</p>
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<pre class="programlisting">#include <cassert>
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#include <stdexcept>
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#include <iostream>
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#include "../include/safe_range.hpp"
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void detected_msg(bool detected){
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std::cout << (detected ? "error detected!" : "error NOT detected! ") << std::endl;
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}
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int main(int argc, const char * argv[]){
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// problem: array index values can exceed array bounds
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std::cout << "example 5: ";
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std::cout << "array index values can exceed array bounds" << std::endl;
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std::cout << "Not using safe numerics" << std::endl;
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int i_array[37];
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unsigned int i_index = 43;
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// the following corrupts memory.
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// This may or may not be detected at run time.
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// i_array[i_index] = 84; // comment this out so it can be tested!
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detected_msg(false);
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// solution: replace unsigned array index with safe_unsigned_range
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std::cout << "Using safe numerics" << std::endl;
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try{
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using namespace boost::numeric;
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safe_unsigned_range<0, sizeof(i_array)/sizeof(int) - 1> i_index;
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i_index = 36; // this works fine
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i_array[i_index] = 84;
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i_index = 37; // throw exception here!
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i_array[i_index] = 84; // so we never arrive here
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assert(false);
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}
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catch(std::exception & e){
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std::cout << e.what() << std::endl;
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detected_msg(true);
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}
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return 0;
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}
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</pre>
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<td align="left"></td>
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<td align="right"><div class="copyright-footer">Copyright © 2012 Robert Ramey<p><a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">Subject to Boost
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Software License</a></p>
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</div></td>
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