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    <h1>Rules of thumb for <em>C++11:</em></h1> <p>Pass <strong><em>by value</em></strong>, except when </p> <ol> <li>you do not need ownership of the object and a simple alias will do, in which case you <strong><em>pass by <code>const</code> reference</em></strong>, </li> <li>you must mutate the object, in which case, use <strong><em>pass by a non-<code>const</code> lvalue reference</em></strong>,</li> <li>you pass objects of derived classes as base classes, in which case you need to <strong><em>pass by reference</em></strong>. (Use the previous rules to determine whether to pass by <code>const</code> reference or not.) </li> </ol> <p>Passing by pointer is virtually never advised. Optional parameters are best expressed as a <code>boost::optional</code>, and aliasing is done fine by reference.</p> <p>C++11's move semantics make passing and returning by value much more attractive even for complex objects.</p> <hr> <h1>Rules of thumb for <em>C++03:</em></h1> <p>Pass arguments <strong><em>by <code>const</code> reference</em></strong>, except when </p> <ol> <li>they are to be changed inside the function and such changes should be reflected outside, in which case you <strong><em>pass by non-<code>const</code> reference</em></strong></li> <li>the function should be callable without any argument, in which case you pass by pointer, so that users can pass <code>NULL</code>/<code>0</code>/<code>nullptr</code> instead; apply the previous rule to determine whether you should <strong><em>pass by a pointer to a <code>const</code> argument</em></strong></li> <li>they are of built-in types, which can be <strong><em>passed by copy</em></strong></li> <li>they are to be changed inside the function and such changes should <strong><em>not</em></strong> be reflected outside, in which case you can <strong><em>pass by copy</em></strong> (an alternative would be to pass according to the previous rules and make a copy inside of the function) </li> </ol> <p>(here, "pass by value" is called "pass by copy", because passing by value always creates a copy in C++03)</p> <hr> <p>There's more to this, but these few beginner's rules will get you quite far. </p>
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    1. POHow to pass objects to functions in C++?
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    1. POHow to pass objects to functions in C++?
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    1. CO+1 - I would also note that some (i.e. Google) feel that objects that will be changed within the function should be passed via a pointer instead of a non-const reference. The reasoning being that when the address of an object is passed to a function it is more apparent that said function may change it. Example: With references, the call is foo(bar); whether the reference is const or not, with a pointer it is foo(&bar); and is more apparent that foo is being passed a mutable object.
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    2. CO@RC Still doesn't tell you if the pointer is const or not. Google's guidelines have come in for a lot of flak in the various C++ online communities - justifiably so, IMHO.
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    3. COWhile in other contexts google may be leading the way, in C++ their style guide is not really that good.
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      1. USDavid Rodríguez - dribeas
 

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