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  47. <a name="mallinfo"></a>
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  49. <p>
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  53. <a name="mallinfo_002c-malloc_005fstats_002c-mallopt_002d_002d_002dmalloc-support"></a>
  54. <h3 class="section">2.25 <code>mallinfo</code>, <code>malloc_stats</code>, <code>mallopt</code>&mdash;malloc support</h3>
  55. <a name="index-mallinfo"></a>
  56. <a name="index-malloc_005fstats"></a>
  57. <a name="index-mallopt"></a>
  58. <a name="index-_005fmallinfo_005fr"></a>
  59. <a name="index-_005fmalloc_005fstats_005fr"></a>
  60. <a name="index-_005fmallopt_005fr"></a>
  61. <p><strong>Synopsis</strong>
  62. </p><div class="example">
  63. <pre class="example">#include &lt;malloc.h&gt;
  64. struct mallinfo mallinfo(void);
  65. void malloc_stats(void);
  66. int mallopt(int <var>parameter</var>, <var>value</var>);
  67. struct mallinfo _mallinfo_r(void *<var>reent</var>);
  68. void _malloc_stats_r(void *<var>reent</var>);
  69. int _mallopt_r(void *<var>reent</var>, int <var>parameter</var>, <var>value</var>);
  70. </pre></div>
  71. <p><strong>Description</strong><br>
  72. <code>mallinfo</code> returns a structure describing the current state of
  73. memory allocation. The structure is defined in malloc.h. The
  74. following fields are defined: <code>arena</code> is the total amount of space
  75. in the heap; <code>ordblks</code> is the number of chunks which are not in use;
  76. <code>uordblks</code> is the total amount of space allocated by <code>malloc</code>;
  77. <code>fordblks</code> is the total amount of space not in use; <code>keepcost</code> is
  78. the size of the top most memory block.
  79. </p>
  80. <p><code>malloc_stats</code> print some statistics about memory allocation on
  81. standard error.
  82. </p>
  83. <p><code>mallopt</code> takes a parameter and a value. The parameters are defined
  84. in malloc.h, and may be one of the following: <code>M_TRIM_THRESHOLD</code>
  85. sets the maximum amount of unused space in the top most block before
  86. releasing it back to the system in <code>free</code> (the space is released by
  87. calling <code>_sbrk_r</code> with a negative argument); <code>M_TOP_PAD</code> is the
  88. amount of padding to allocate whenever <code>_sbrk_r</code> is called to
  89. allocate more space.
  90. </p>
  91. <p>The alternate functions <code>_mallinfo_r</code>, <code>_malloc_stats_r</code>, and
  92. <code>_mallopt_r</code> are reentrant versions. The extra argument <var>reent</var>
  93. is a pointer to a reentrancy structure.
  94. </p>
  95. <br>
  96. <p><strong>Returns</strong><br>
  97. <code>mallinfo</code> returns a mallinfo structure. The structure is defined
  98. in malloc.h.
  99. </p>
  100. <p><code>malloc_stats</code> does not return a result.
  101. </p>
  102. <p><code>mallopt</code> returns zero if the parameter could not be set, or
  103. non-zero if it could be set.
  104. </p>
  105. <br>
  106. <p><strong>Portability</strong><br>
  107. <code>mallinfo</code> and <code>mallopt</code> are provided by SVR4, but <code>mallopt</code>
  108. takes different parameters on different systems. <code>malloc_stats</code> is
  109. not portable.
  110. </p>
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