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  53. <a name="assert_002d_002d_002dmacro-for-debugging-diagnostics"></a>
  54. <h3 class="section">2.5 <code>assert</code>&mdash;macro for debugging diagnostics</h3>
  55. <a name="index-assert"></a>
  56. <p><strong>Synopsis</strong>
  57. </p><div class="example">
  58. <pre class="example">#include &lt;assert.h&gt;
  59. void assert(int <var>expression</var>);
  60. </pre></div>
  61. <p><strong>Description</strong><br>
  62. Use this macro to embed debuggging diagnostic statements in
  63. your programs. The argument <var>expression</var> should be an
  64. expression which evaluates to true (nonzero) when your program
  65. is working as you intended.
  66. </p>
  67. <p>When <var>expression</var> evaluates to false (zero), <code>assert</code>
  68. calls <code>abort</code>, after first printing a message showing what
  69. failed and where:
  70. </p>
  71. <div class="smallexample">
  72. <pre class="smallexample"> Assertion failed: <var>expression</var>, file <var>filename</var>, line <var>lineno</var>, function: <var>func</var>
  73. </pre></div>
  74. <p>If the name of the current function is not known (for example,
  75. when using a C89 compiler that does not understand __func__),
  76. the function location is omitted.
  77. </p>
  78. <p>The macro is defined to permit you to turn off all uses of
  79. <code>assert</code> at compile time by defining <code>NDEBUG</code> as a
  80. preprocessor variable. If you do this, the <code>assert</code> macro
  81. expands to
  82. </p>
  83. <div class="smallexample">
  84. <pre class="smallexample"> (void(0))
  85. </pre></div>
  86. <br>
  87. <p><strong>Returns</strong><br>
  88. <code>assert</code> does not return a value.
  89. </p>
  90. <br>
  91. <p><strong>Portability</strong><br>
  92. The <code>assert</code> macro is required by ANSI, as is the behavior
  93. when <code>NDEBUG</code> is defined.
  94. </p>
  95. <p>Supporting OS subroutines required (only if enabled): <code>close</code>, <code>fstat</code>,
  96. <code>getpid</code>, <code>isatty</code>, <code>kill</code>, <code>lseek</code>, <code>read</code>, <code>sbrk</code>, <code>write</code>.
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