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<html><!-- #BeginTemplate "/Templates/tmpl.dwt" --><head><!-- #BeginEditable "doctitle" --> <title>PTypes: variant: arrays</title><!-- #EndEditable --> <meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1"><link rel="stylesheet" href="styles.css"></head><body bgcolor="#FFFFFF" leftmargin="40" marginwidth="40"><p><a href="../index.html"><img src="title-1.7.gif" width="213" height="34" alt="C++ Portable Types Library (PTypes) Version 1.7" border="0"></a> <hr noshade><!-- #BeginEditable "body" --> <p class="hpath"><a href="index.html">Top</a>: <a href="basic.html">Basic types</a>: <a href="variant.html">variant</a>: Arrays</p><blockquote> <pre class="lang">#include <ptypes.h> void aclear(variant& a);<br>variant aclone(const variant& a);void put(variant& a, <i><key></i>, const variant& item);const variant& get(const variant& a, <i><key></i>);const variant& variant::operator[](<i><key></i>) const;void del(variant& a, <i><key></i>);int alength(const variant& a);bool anext(const variant& array, int& index, variant& item);</pre></blockquote><p>A variant object can hold an associative array of variants. The variant changes its type to an array as soon as <span class="lang">put()</span> or <span class="lang">aclear()</span> is called for an object. When assigning variants, only a reference to an array is being copied, which means, modifying an array through one variant object affects all other objects that hold a reference to the same array. To duplicate the contents of an array use <span class="lang">aclone()</span>.</p><p>PTypes uses reference counting on arrays to properly clean up unused dynamic structures. However, since variant arrays may recursively contain arrays and in some situations there may be a circular reference, it is possible to have memory leak when using such structures. Since PTypes does not provide garbage collection (e.g. like in Java), compound variant data structures should be designed so that variants never reference each other circularly.</p><p><span class="def">void aclear(variant& a)</span> clears the variant array. This function may affect other variant objects holding a reference to the same array data.</p><p><span class="def">variant aclone(const variant& a)</span> creates a copy of an array or creates an empty array if <span class="lang">a</span> is of any other variant type. If <span class="lang">a</span> contains variant arrays as elements, only their references are being copied.</p><p><span class="def">void put(variant& a, <i><key></i>, const variant& item)</span> associates <span class="lang">item</span> with <span class="lang">key</span> in the variant array <span class="lang">a</span>. <span class="lang">Key</span> can be either a string or an integer. The previous value associated with this key, if any, is replaced with the new value. <span class="lang"></span>If <span class="lang">item</span> is an unassigned variant, the new value is not stored in the array.</p><p><span class="def">const variant& get(const variant& a, <i><key></i>)</span> retrieves an element associated with <span class="lang">key</span> in the array <span class="lang">a</span>. If the element does not exist, or <span class="lang">a</span> is not an array, this function returns an unassigned variant (a reference to <span class="lang">nullvar</span>). <span class="lang">Key</span> can be either a string or an integer. Variant arrays use hashing to retrieve elements by keys.</p><p><span class="def">const variant& variant::operator[](<i><key></i>)</span> equivalent to <span class="lang">get()</span>. This operator can be used only for retrieving elements.</p><p><span class="def">void del(variant& a, <i><key></i>)</span> removes the element associated with <span class="lang">key</span> from the array <span class="lang">a</span>. Does nothing if the element does not exist or <span class="lang">a</span> is not an array. Equivalent to calling <span class="lang">put()</span> with an unassigned variant item.</p><p><span class="def">int alength(const variant& a)</span> returns the length of an array.</p><p><span class="def">bool anext(const variant& a, int& index, variant& item)</span> iterates through array elements (please see examples in the introduction to variants). Each time <span class="lang">anext()</span> is called it assigns the next item in the array to <span class="lang">item</span>. <span class="lang">Index</span> must be zero when calling this function first time; it will be then incremented automatically. If there are no items left in the array (<span class="lang">index</span> is out of range), or <span class="lang">a</span> is not an array, this function returns <span class="lang">false</span>.</p><p class="seealso">See also: <a href="string.html">string</a>, <a href="variant.typecasts.html">Assignments and typecasts</a>, <a href="variant.objrefs.html">Object references</a>, <a href="variant.utils.html">Utilities</a></p><!-- #EndEditable --> <hr size="1"><a href="../index.html" class="ns">PTypes home</a></body><!-- #EndTemplate --></html>⌨️ 快捷键说明
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