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<p><a href="../index.html"><img src="title-21.png" width="253" height="39" alt="C++ Portable Types Library (PTypes) Version 2.1" border="0"></a>
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<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>);
bool anext(const variant& array, int& index, variant& item, [ string& key ]);
</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>Variant arrays can associate values with either strings or integers (32 or
64 bit). Integer keys are not required to be consecutive. It should be noted that
in the current implementation there is no difference in performance between these
two methods. Both methods can be mixed in one array.</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 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">bool anext(const variant& a, int& index, variant&
item, [ string& key ])</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>
and optionally assigns its key value to <span class="lang">key</span>. <span class="lang">Index</span>
must be zero when calling this function first time. If there are no items left
in the array, 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>
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