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copied!<p>It really depends on whether you know if <code>o</code> is a string and what you want to do with it. If your comment means that <code>o</code> really really is a string, I'd prefer the straight <code>(string)o</code> cast - it's unlikely to fail.</p> <p>The biggest advantage of using the straight cast is that when it fails, you get an <a href="http://msdn.microsoft.com/en-us/library/system.invalidcastexception.aspx" rel="noreferrer">InvalidCastException</a>, which tells you pretty much what went wrong.</p> <p>With the <code>as</code> operator, if <code>o</code> isn't a string, <code>s</code> is set to <code>null</code>, which is handy if you're unsure and want to test <code>s</code>:</p> <pre><code>string s = o as string; if ( s == null ) { // well that's not good! gotoPlanB(); } </code></pre> <p>However, if you don't perform that test, you'll use <code>s</code> later and have a <a href="http://msdn.microsoft.com/en-us/library/system.nullreferencetexception.aspx" rel="noreferrer">NullReferenceException</a> thrown. These tend to be more common and a <em>lot</em> harder to track down once they happens out in the wild, as nearly every line dereferences a variable and may throw one. On the other hand, if you're trying to cast to a value type (any primitive, or structs such as <a href="http://msdn.microsoft.com/en-us/library/system.datetime.aspx" rel="noreferrer">DateTime</a>), you have to use the straight cast - the <code>as</code> won't work.</p> <p>In the special case of converting to a string, every object has a <code>ToString</code>, so your third method may be okay if <code>o</code> isn't null and you think the <code>ToString</code> method might do what you want.</p>

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