qtscriptclassic/doc/html/qscriptengine-obsolete.html


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  <title>Obsolete Members for QScriptEngine</title>
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</tr></table><h1 class="title">Obsolete Members for QScriptEngine</h1>
<p><b>The following class members are obsolete.</b> They are provided to keep old source code working. We strongly advise against using them in new code.</p>
<p><ul><li><a href="qscriptengine.html">QScriptEngine class reference</a></li></ul></p>
<h2>Public Functions</h2>
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<tr><td class="memItemLeft" align="right" valign="top">bool </td><td class="memItemRight" valign="bottom"><b><a href="qscriptengine-obsolete.html#canEvaluate">canEvaluate</a></b> ( const QString &amp; <i>program</i> ) const&nbsp;&nbsp;<tt> (obsolete)</tt></td></tr>
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<h2>Member Function Documentation</h2>
<h3 class="fn"><a name="canEvaluate"></a>bool QScriptEngine::canEvaluate ( const <a href="http://qt.nokia.com/doc/4.6/qstring.html">QString</a> &amp; <i>program</i> ) const</h3>
<p>Returns true if <i>program</i> can be evaluated; i.e&#x2e; the code is sufficient to determine whether it appears to be a syntactically correct program, or contains a syntax error.</p>
<p>This function returns false if <i>program</i> is incomplete; i.e&#x2e; the input is syntactically correct up to the point where the input is terminated.</p>
<p>Note that this function only does a static check of <i>program</i>; e.g&#x2e; it does not check whether references to variables are valid, and so on.</p>
<p>A typical usage of canEvaluate() is to implement an interactive interpreter for <a href="http://qt.nokia.com/doc/4.6/qtscript.html">QtScript</a>. The user is repeatedly queried for individual lines of code; the lines are concatened internally, and only when canEvaluate() returns true for the resulting program is it passed to <a href="qscriptengine.html#evaluate">evaluate</a>().</p>
<p>The following are some examples to illustrate the behavior of canEvaluate(). (Note that all example inputs are assumed to have an explicit newline as their last character, since otherwise the <a href="http://qt.nokia.com/doc/4.6/qtscript.html">QtScript</a> parser would automatically insert a semi-colon character at the end of the input, and this could cause canEvaluate() to produce different results.)</p>
<p>Given the input</p>
<pre> if (hello &amp;&amp; world)
     print(&quot;hello world&quot;);</pre>
<p>canEvaluate() will return true, since the program appears to be complete.</p>
<p>Given the input</p>
<pre> if (hello &amp;&amp;</pre>
<p>canEvaluate() will return false, since the if-statement is not complete, but is syntactically correct so far.</p>
<p>Given the input</p>
<pre> 0 = 0</pre>
<p>canEvaluate() will return true, but <a href="qscriptengine.html#evaluate">evaluate</a>() will throw a SyntaxError given the same input.</p>
<p>Given the input</p>
<pre> ./test.js</pre>
<p>canEvaluate() will return true, even though the code is clearly not syntactically valid <a href="http://qt.nokia.com/doc/4.6/qtscript.html">QtScript</a> code. <a href="qscriptengine.html#evaluate">evaluate</a>() will throw a SyntaxError when this code is evaluated.</p>
<p>Given the input</p>
<pre> foo[&quot;bar&quot;]</pre>
<p>canEvaluate() will return true, but <a href="qscriptengine.html#evaluate">evaluate</a>() will throw a ReferenceError if <tt>foo</tt> is not defined in the script environment.</p>
<p>See also <a href="qscriptengine.html#evaluate">evaluate</a>() and <a href="qscriptengine.html#checkSyntax">checkSyntax</a>().</p>
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