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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>:
variant </p>
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<h5><a href="variant.typecasts.html">Assignments and typecasts</a></h5>
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<h5><a href="variant.arrays.html">Arrays</a></h5>
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<h5><a href="variant.objrefs.html">Object references</a></h5>
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<h5><a href="variant.utils.html">Utilities</a></h5>
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<p>The <span class="lang">variant</span> class offers a universal and flexible
way to store values whose types can not be determined at compile time. A variant
object can hold integer, boolean, floating point or string values as well as associative
arrays of variants or references to objects derived from <span class="lang">component</span>.
Variants can change their types at run-time. In return for their flexibility,
variants have some memory usage and performance overhead. They always occupy 12
bytes of static or local memory, however, they may also use dynamic memory allocation
for strings and arrays.</p>
<p>The <span class="lang">variant</span> class provides all possible automatic
typecasts, so that in most cases, when variants are used in assignments and function
calls, the compiler will generate implicit typecasts appropriate for the context.
The typecast functions always try to perform conversion regardless of the current
and target types, although it may not always be sensible. For example, if a variant
object holds an integer value, an attempt to cast it to a string will result in
converting the value to its string representation; if a variant is an associative
array, an attempt to cast it to boolean will return true if the array is not empty.
Variant typecast routines never generate errors except when a 64-bit integer value
is converted to 32-bit int and the value exceeds the allowed range.</p>
<p>A variant variable may itself represent an associative array of variants. </p>
<p>This interface can be useful for (but not limited to) designing interpreters
and compilers, working with databases and spreadsheets, etc. </p>
<p>The variant class is declared in <a href="include/ptypes.h.html"><ptypes.h></a>.</p>
<p><b>Examples</b></p>
<blockquote>
<pre>variant v1 = 11;
variant v2 = "33";
variant v3 = int(v1) + int(v2) + 22; <span class="comment">// explicit typecasts: without them the compiler can't</span>
variant v4 = string(v2) + " cows"; <span class="comment">// figure out which of + operators to use here</span>
large i1 = v1; <span class="comment">// implicit typecast is possible here</span>
int a = v2; <span class="comment">// large-to-int: may generate (evariant*) exception</span>
variant v5;
put(v5, "key1", v1); <span class="comment">// variants may be associated with both strings and</span>
put(v5, 15, "value2"); <span class="comment">// integer values in variant arrays</span>
variant v6 = v5[15];
variant v7 = v5; <span class="comment">// a reference to the array is passed</span>
variant varray = aclone(v5); <span class="comment">// array is duplicated</span>
variant item; <span class="comment"> // array iteration example</span>
for (int i = 0; anext(varray, i, item); )
pout.putf("%d: %d\n", i, int(item));<br></pre>
</blockquote>
<p class="seealso">See also: <a href="string.html">string</a>, <a href="unknown.html">unknown
& component</a>, <a href="variant.typecasts.html">Assignments and typecasts</a>,
<a href="variant.arrays.html">Arrays</a>, <a href="variant.objrefs.html">Object
references</a>, <a href="variant.utils.html">Utilities</a></p>
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