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a) made trap_exception work b) updated manual and examples to show how to use library to eliminate runtime penalty c) added in safe_literal d) made corrections of various types
87 lines
4.3 KiB
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87 lines
4.3 KiB
HTML
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<title>Array Index Value Can Exceed Array Limits</title>
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<td valign="top"><img href="index.html" height="164px" src="pre-boost.jpg" alt="Library Documentation Index"></td>
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<td><h2>Safe Numerics</h2></td>
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<a accesskey="p" href="10.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="section">
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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 <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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std::array<int, 37> i_array;
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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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std::cout << "error NOT detected!" << std::endl;
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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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using i_index_t = safe_unsigned_range<0, i_array.size() - 1>;
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i_index_t 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 = 43; // throw exception here!
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std::cout << "error NOT detected!" << std::endl; // so we never arrive here
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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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std::cout << "error detected!" << std::endl;
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}
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return 0;
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}
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</pre>
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<p>Collections
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like standard arrays, vectors do array index checking in some function
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calls and not in others so this may not be the best example. However it
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does illustrate the usage of <code class="computeroutput">safe_range<T></code> for
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assigning legal range to variables. This will guarantee that under no
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circumstances will the variable contain a value outside of the specified
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range.</p>
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</div>
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<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
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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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