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- <a name="mallinfo_002c-malloc_005fstats_002c-mallopt_002d_002d_002dmalloc-support"></a>
- <h3 class="section">2.25 <code>mallinfo</code>, <code>malloc_stats</code>, <code>mallopt</code>—malloc support</h3>
- <a name="index-mallinfo"></a>
- <a name="index-malloc_005fstats"></a>
- <a name="index-mallopt"></a>
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- <p><strong>Synopsis</strong>
- </p><div class="example">
- <pre class="example">#include <malloc.h>
- struct mallinfo mallinfo(void);
- void malloc_stats(void);
- int mallopt(int <var>parameter</var>, <var>value</var>);
-
- struct mallinfo _mallinfo_r(void *<var>reent</var>);
- void _malloc_stats_r(void *<var>reent</var>);
- int _mallopt_r(void *<var>reent</var>, int <var>parameter</var>, <var>value</var>);
-
- </pre></div>
- <p><strong>Description</strong><br>
- <code>mallinfo</code> returns a structure describing the current state of
- memory allocation. The structure is defined in malloc.h. The
- following fields are defined: <code>arena</code> is the total amount of space
- in the heap; <code>ordblks</code> is the number of chunks which are not in use;
- <code>uordblks</code> is the total amount of space allocated by <code>malloc</code>;
- <code>fordblks</code> is the total amount of space not in use; <code>keepcost</code> is
- the size of the top most memory block.
- </p>
- <p><code>malloc_stats</code> print some statistics about memory allocation on
- standard error.
- </p>
- <p><code>mallopt</code> takes a parameter and a value. The parameters are defined
- in malloc.h, and may be one of the following: <code>M_TRIM_THRESHOLD</code>
- sets the maximum amount of unused space in the top most block before
- releasing it back to the system in <code>free</code> (the space is released by
- calling <code>_sbrk_r</code> with a negative argument); <code>M_TOP_PAD</code> is the
- amount of padding to allocate whenever <code>_sbrk_r</code> is called to
- allocate more space.
- </p>
- <p>The alternate functions <code>_mallinfo_r</code>, <code>_malloc_stats_r</code>, and
- <code>_mallopt_r</code> are reentrant versions. The extra argument <var>reent</var>
- is a pointer to a reentrancy structure.
- </p>
- <br>
- <p><strong>Returns</strong><br>
- <code>mallinfo</code> returns a mallinfo structure. The structure is defined
- in malloc.h.
- </p>
- <p><code>malloc_stats</code> does not return a result.
- </p>
- <p><code>mallopt</code> returns zero if the parameter could not be set, or
- non-zero if it could be set.
- </p>
- <br>
- <p><strong>Portability</strong><br>
- <code>mallinfo</code> and <code>mallopt</code> are provided by SVR4, but <code>mallopt</code>
- takes different parameters on different systems. <code>malloc_stats</code> is
- not portable.
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