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  4. <title>Checking of Input Values Can Be Easily Overlooked</title>
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  14. <td valign="top"><img href="index.html" height="164px" src="pre-boost.jpg" alt="Library Documentation Index"></td>
    15. 

  15. <td><h2>Safe Numerics</h2></td>
    16. 

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  19. </div>
    20. 

  20. <div class="section">
    21. 

  21. <div class="titlepage"><div><div><h3 class="title">
    22. 

  22. <a name="safe_numerics.tutorial.7"></a>Checking of Input Values Can Be Easily Overlooked</h3></div></div></div>
    23. 

  23. <p>It's way too easy to overlook the checking of parameters received
    24. 

  24.     from outside the current program.</p>
    25. 

  25. <pre class="programlisting"><span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">stdexcept</span><span class="special">&gt;</span>
    26. 

  26. <span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">sstream</span><span class="special">&gt;</span>
    27. 

  27. <span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">iostream</span><span class="special">&gt;</span>
    28. 

  28. 

  29. <span class="preprocessor">#include</span> <span class="special">&lt;</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">safe_numerics</span><span class="special">/</span><span class="identifier">safe_integer</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">&gt;</span>
    30. 

  30. 

  31. <span class="keyword">int</span> <span class="identifier">main</span><span class="special">(</span><span class="keyword">int</span><span class="special">,</span> <span class="keyword">const</span> <span class="keyword">char</span> <span class="special">*</span><span class="special">[</span><span class="special">]</span><span class="special">)</span><span class="special">{</span>
    32. 

  32.     <span class="comment">// problem: checking of externally produced value can be overlooked</span>
    33. 

  33.     <span class="identifier">std</span><span class="special">::</span><span class="identifier">cout</span> <span class="special">&lt;&lt;</span> <span class="string">"example 6: "</span><span class="special">;</span>
    34. 

  34.     <span class="identifier">std</span><span class="special">::</span><span class="identifier">cout</span> <span class="special">&lt;&lt;</span> <span class="string">"checking of externally produced value can be overlooked"</span> <span class="special">&lt;&lt;</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">endl</span><span class="special">;</span>
    35. 

  35.     <span class="identifier">std</span><span class="special">::</span><span class="identifier">cout</span> <span class="special">&lt;&lt;</span> <span class="string">"Not using safe numerics"</span> <span class="special">&lt;&lt;</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">endl</span><span class="special">;</span>
    36. 

  36. 

  37.     <span class="identifier">std</span><span class="special">::</span><span class="identifier">istringstream</span> <span class="identifier">is</span><span class="special">(</span><span class="string">"12317289372189 1231287389217389217893"</span><span class="special">)</span><span class="special">;</span>
    38. 

  38. 

  39.     <span class="keyword">try</span><span class="special">{</span>
    40. 

  40.         <span class="keyword">int</span> <span class="identifier">x</span><span class="special">,</span> <span class="identifier">y</span><span class="special">;</span>
    41. 

  41.         <span class="identifier">is</span> <span class="special">&gt;&gt;</span> <span class="identifier">x</span> <span class="special">&gt;&gt;</span> <span class="identifier">y</span><span class="special">;</span> <span class="comment">// get integer values from the user</span>
    42. 

  42.         <span class="identifier">std</span><span class="special">::</span><span class="identifier">cout</span> <span class="special">&lt;&lt;</span> <span class="identifier">x</span> <span class="special">&lt;&lt;</span> <span class="char">' '</span> <span class="special">&lt;&lt;</span> <span class="identifier">y</span> <span class="special">&lt;&lt;</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">endl</span><span class="special">;</span>
    43. 

  43.         <span class="identifier">std</span><span class="special">::</span><span class="identifier">cout</span> <span class="special">&lt;&lt;</span> <span class="string">"error NOT detected!"</span> <span class="special">&lt;&lt;</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">endl</span><span class="special">;</span>
    44. 

  44.     <span class="special">}</span>
    45. 

  45.     <span class="keyword">catch</span><span class="special">(</span><span class="keyword">const</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">exception</span> <span class="special">&amp;</span><span class="special">)</span><span class="special">{</span>
    46. 

  46.         <span class="identifier">std</span><span class="special">::</span><span class="identifier">cout</span> <span class="special">&lt;&lt;</span> <span class="string">"error detected!"</span> <span class="special">&lt;&lt;</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">endl</span><span class="special">;</span>
    47. 

  47.     <span class="special">}</span>
    48. 

  48. 

  49.     <span class="comment">// solution: assign externally retrieved values to safe equivalents</span>
    50. 

  50.     <span class="identifier">std</span><span class="special">::</span><span class="identifier">cout</span> <span class="special">&lt;&lt;</span> <span class="string">"Using safe numerics"</span> <span class="special">&lt;&lt;</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">endl</span><span class="special">;</span>
    51. 

  51.     <span class="special">{</span>
    52. 

  52.         <span class="keyword">using</span> <span class="keyword">namespace</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">safe_numerics</span><span class="special">;</span>
    53. 

  53.         <span class="identifier">safe</span><span class="special">&lt;</span><span class="keyword">int</span><span class="special">&gt;</span> <span class="identifier">x</span><span class="special">,</span> <span class="identifier">y</span><span class="special">;</span>
    54. 

  54.         <span class="identifier">is</span><span class="special">.</span><span class="identifier">seekg</span><span class="special">(</span><span class="number">0</span><span class="special">)</span><span class="special">;</span>
    55. 

  55.         <span class="keyword">try</span><span class="special">{</span>
    56. 

  56.             <span class="identifier">is</span> <span class="special">&gt;&gt;</span> <span class="identifier">x</span> <span class="special">&gt;&gt;</span> <span class="identifier">y</span><span class="special">;</span> <span class="comment">// get integer values from the user</span>
    57. 

  57.             <span class="identifier">std</span><span class="special">::</span><span class="identifier">cout</span> <span class="special">&lt;&lt;</span> <span class="identifier">x</span> <span class="special">&lt;&lt;</span> <span class="char">' '</span> <span class="special">&lt;&lt;</span> <span class="identifier">y</span> <span class="special">&lt;&lt;</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">endl</span><span class="special">;</span>
    58. 

  58.             <span class="identifier">std</span><span class="special">::</span><span class="identifier">cout</span> <span class="special">&lt;&lt;</span> <span class="string">"error NOT detected!"</span> <span class="special">&lt;&lt;</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">endl</span><span class="special">;</span>
    59. 

  59.         <span class="special">}</span>
    60. 

  60.         <span class="keyword">catch</span><span class="special">(</span><span class="keyword">const</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">exception</span> <span class="special">&amp;</span> <span class="identifier">e</span><span class="special">)</span><span class="special">{</span>
    61. 

  61.             <span class="identifier">std</span><span class="special">::</span><span class="identifier">cout</span> <span class="special">&lt;&lt;</span> <span class="string">"error detected:"</span>  <span class="special">&lt;&lt;</span> <span class="identifier">e</span><span class="special">.</span><span class="identifier">what</span><span class="special">(</span><span class="special">)</span> <span class="special">&lt;&lt;</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">endl</span><span class="special">;</span>
    62. 

  62.         <span class="special">}</span>
    63. 

  63.     <span class="special">}</span>
    64. 

  64.     <span class="keyword">return</span> <span class="number">0</span><span class="special">;</span>
    65. 

  65. <span class="special">}</span>
    66. 

  66. </pre>
    67. 

  67. <pre class="screen">example 6: checking of externally produced value can be overlooked
    68. 

  68. Not using safe numerics
    69. 

  69. 2147483647 0
    70. 

  70. error NOT detected!
    71. 

  71. Using safe numerics
    72. 

  72. error detected:error in file input: domain error
    73. 

  73. </pre>
    74. 

  74. <p>Without safe integer, one will have to insert new code every time an
    75. 

  75.     integer variable is retrieved. This is a tedious and error prone
    76. 

  76.     procedure. Here we have used program input. But in fact this problem can
    77. 

  77.     occur with any externally produced input.</p>
    78. 

  78. </div>
    79. 

  79. <table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
    80. 

  80. <td align="left"></td>
    81. 

  81. <td align="right"><div class="copyright-footer">Copyright &#169; 2012-2018 Robert Ramey<p><a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">Subject to Boost
    82. 

  82.       Software License</a></p>
    83. 

  83. </div></td>
    84. 

  84. </tr></table>
    85. 

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    86. 

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    88. 

  88. </div>
    89. 

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    91.