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- Next: <a href="atexit.html#atexit" accesskey="n" rel="next">atexit</a>, Previous: <a href="abs.html#abs" accesskey="p" rel="prev">abs</a>, Up: <a href="Stdlib.html#Stdlib" accesskey="u" rel="up">Stdlib</a> [<a href="Document-Index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Document-Index.html#Document-Index" title="Index" rel="index">Index</a>]</p>
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- <a name="assert_002d_002d_002dmacro-for-debugging-diagnostics"></a>
- <h3 class="section">2.5 <code>assert</code>—macro for debugging diagnostics</h3>
- <a name="index-assert"></a>
- <p><strong>Synopsis</strong>
- </p><div class="example">
- <pre class="example">#include <assert.h>
- void assert(int <var>expression</var>);
-
- </pre></div>
- <p><strong>Description</strong><br>
- Use this macro to embed debuggging diagnostic statements in
- your programs. The argument <var>expression</var> should be an
- expression which evaluates to true (nonzero) when your program
- is working as you intended.
- </p>
- <p>When <var>expression</var> evaluates to false (zero), <code>assert</code>
- calls <code>abort</code>, after first printing a message showing what
- failed and where:
- </p>
- <div class="smallexample">
- <pre class="smallexample"> Assertion failed: <var>expression</var>, file <var>filename</var>, line <var>lineno</var>, function: <var>func</var>
- </pre></div>
-
- <p>If the name of the current function is not known (for example,
- when using a C89 compiler that does not understand __func__),
- the function location is omitted.
- </p>
- <p>The macro is defined to permit you to turn off all uses of
- <code>assert</code> at compile time by defining <code>NDEBUG</code> as a
- preprocessor variable. If you do this, the <code>assert</code> macro
- expands to
- </p>
- <div class="smallexample">
- <pre class="smallexample"> (void(0))
- </pre></div>
-
- <br>
- <p><strong>Returns</strong><br>
- <code>assert</code> does not return a value.
- </p>
- <br>
- <p><strong>Portability</strong><br>
- The <code>assert</code> macro is required by ANSI, as is the behavior
- when <code>NDEBUG</code> is defined.
- </p>
- <p>Supporting OS subroutines required (only if enabled): <code>close</code>, <code>fstat</code>,
- <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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