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GNU Compiler Collection (GCC) Internals

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7.4.2 Classes

A class type is represented by either a RECORD_TYPE or a UNION_TYPE. A class declared with the union tag is represented by a UNION_TYPE, while classes declared with either the struct or the class tag are represented by RECORD_TYPEs. You can use the CLASSTYPE_DECLARED_CLASS macro to discern whether or not a particular type is a class as opposed to a struct. This macro will be true only for classes declared with the class tag.

Almost all non-function members are available on the TYPE_FIELDS list. Given one member, the next can be found by following the TREE_CHAIN. You should not depend in any way on the order in which fields appear on this list. All nodes on this list will be `DECL' nodes. A FIELD_DECL is used to represent a non-static data member, a VAR_DECL is used to represent a static data member, and a TYPE_DECL is used to represent a type. Note that the CONST_DECL for an enumeration constant will appear on this list, if the enumeration type was declared in the class. (Of course, the TYPE_DECL for the enumeration type will appear here as well.) There are no entries for base classes on this list. In particular, there is no FIELD_DECL for the "base-class portion" of an object.

The TYPE_VFIELD is a compiler-generated field used to point to virtual function tables. It may or may not appear on the TYPE_FIELDS list. However, back ends should handle the TYPE_VFIELD just like all the entries on the TYPE_FIELDS list.

The function members are available on the TYPE_METHODS list. Again, subsequent members are found by following the TREE_CHAIN field. If a function is overloaded, each of the overloaded functions appears; no OVERLOAD nodes appear on the TYPE_METHODS list. Implicitly declared functions (including default constructors, copy constructors, assignment operators, and destructors) will appear on this list as well.

Every class has an associated binfo, which can be obtained with TYPE_BINFO. Binfos are used to represent base-classes. The binfo given by TYPE_BINFO is the degenerate case, whereby every class is considered to be its own base-class. The base classes for a particular binfo can be obtained with BINFO_BASETYPES. These base-classes are themselves binfos. The class type associated with a binfo is given by BINFO_TYPE. It is always the case that BINFO_TYPE (TYPE_BINFO (x)) is the same type as x, up to qualifiers. However, it is not always the case that TYPE_BINFO (BINFO_TYPE (y)) is always the same binfo as y. The reason is that if y is a binfo representing a base-class B of a derived class D, then BINFO_TYPE (y) will be B, and TYPE_BINFO (BINFO_TYPE (y)) will be B as its own base-class, rather than as a base-class of D.

The BINFO_BASETYPES is a TREE_VEC (see section 7.2.3 Containers). Base types appear in left-to-right order in this vector. You can tell whether or public, protected, or private inheritance was used by using the TREE_VIA_PUBLIC, TREE_VIA_PROTECTED, and TREE_VIA_PRIVATE macros. Each of these macros takes a BINFO and is true if and only if the indicated kind of inheritance was used. If TREE_VIA_VIRTUAL holds of a binfo, then its BINFO_TYPE was inherited from virtually.

The following macros can be used on a tree node representing a class-type.

This predicate holds if the class is local class i.e. declared inside a function body.

This predicate holds if the class has at least one virtual function (declared or inherited).

This predicate holds whenever its argument represents a class-type with default constructor.

These predicates hold for a class-type having a mutable data member.

This predicate holds only for class-types that are not PODs.

This predicate holds for a class-type that defines operator new.

This predicate holds for a class-type for which operator new[] is defined.

This predicate holds for class-type for which the function call operator() is overloaded.

This predicate holds for a class-type that overloads operator[]

This predicate holds for a class-type for which operator-> is overloaded.

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