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    <h3>Very informally:</h3> <p>A POD is a type (including classes) where the C++ compiler guarantees that there will be no "magic" going on in the structure: for example hidden pointers to vtables, offsets that get applied to the address when it is cast to other types (at least if the target's POD too), constructors, or destructors. Roughly speaking, a type is a POD when the only things in it are built-in types and combinations of them. The result is something that "acts like" a C type.</p> <h3>Less informally:</h3> <ul> <li><code>int</code>, <code>char</code>, <code>wchar_t</code>, <code>bool</code>, <code>float</code>, <code>double</code> are PODs, as are <code>long/short</code> and <code>signed/unsigned</code> versions of them.</li> <li>pointers (including pointer-to-function and pointer-to-member) are PODs, </li> <li><code>enums</code> are PODs</li> <li>a <code>const</code> or <code>volatile</code> POD is a POD.</li> <li>a <code>class</code>, <code>struct</code> or <code>union</code> of PODs is a POD provided that all non-static data members are <code>public</code>, and it has no base class and no constructors, destructors, or virtual methods. Static members don't stop something being a POD under this rule.</li> <li>Wikipedia is wrong to say that a POD cannot have members of type pointer-to-member. Or rather, it's correct for the C++98 wording, but TC1 made explicit that pointers-to-member are POD.</li> </ul> <h3>Formally (C++03 Standard):</h3> <blockquote> <p><strong>3.9(10):</strong> "Arithmetic types (3.9.1), enumeration types, pointer types, and pointer to member types (3.9.2) and cv-qualified versions of these types (3.9.3) are collectively caller scalar types. Scalar types, POD-struct types, POD-union types (clause 9), arrays of such types and cv-qualified versions of these types (3.9.3) are collectively called POD types"</p> <p><strong>9(4):</strong> "A POD-struct is an aggregate class that has no non-static data members of type non-POD-struct, non-POD-union (or array of such types) or reference, and has no user-define copy operator and no user-defined destructor. Similarly a POD-union is an aggregate union that has no non-static data members of type non-POD-struct, non-POD-union (or array of such types) or reference, and has no user-define copy operator and no user-defined destructor.</p> <p><strong>8.5.1(1):</strong> "An aggregate is an array or class (clause 9) with no user-declared constructors (12.1), no private or protected non-static data members (clause 11), no base classes (clause 10) and no virtual functions (10.3)."</p> </blockquote>
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    1. POWhat are POD types in C++?
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    1. USSteve Jessop
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    1. COYou have formal/less formal. You could add rule of thumb. Built in types and aggregations of Built in types (or something like that). In addition to get the exact definition we need to make the knowledge easy to use.
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      1. USMartin York
    2. COI've added a "roughly speaking" clause. I don't want to say "aggregate" because it's a jargon term, and a casual reader wouldn't know that it means no virtual functions, no private members, etc.
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      1. USSteve Jessop
    3. COYou're a bit wrong on the "offsets when _cast_to_ another type" bit. Those offsets are applied when casting to a base or derived class. So, if you cast from a POD base class pointer to a non-POD derived class, you may still encounter an adjustement.
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