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164 lines
9.3 KiB
HTML
4 years ago
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<html lang="en">
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<head>
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<title>Classes - GNU Compiler Collection (GCC) Internals</title>
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<meta http-equiv="Content-Type" content="text/html">
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<meta name="description" content="GNU Compiler Collection (GCC) Internals">
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<meta name="generator" content="makeinfo 4.13">
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<link title="Top" rel="start" href="index.html#Top">
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<link rel="up" href="C-and-C_002b_002b-Trees.html#C-and-C_002b_002b-Trees" title="C and C++ Trees">
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<link rel="prev" href="Namespaces.html#Namespaces" title="Namespaces">
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<link rel="next" href="Functions-for-C_002b_002b.html#Functions-for-C_002b_002b" title="Functions for C++">
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<link href="http://www.gnu.org/software/texinfo/" rel="generator-home" title="Texinfo Homepage">
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<!--
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Copyright (C) 1988-2015 Free Software Foundation, Inc.
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Permission is granted to copy, distribute and/or modify this document
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under the terms of the GNU Free Documentation License, Version 1.3 or
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any later version published by the Free Software Foundation; with the
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Invariant Sections being ``Funding Free Software'', the Front-Cover
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Texts being (a) (see below), and with the Back-Cover Texts being (b)
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(see below). A copy of the license is included in the section entitled
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``GNU Free Documentation License''.
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(a) The FSF's Front-Cover Text is:
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A GNU Manual
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(b) The FSF's Back-Cover Text is:
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You have freedom to copy and modify this GNU Manual, like GNU
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funds for GNU development.-->
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--></style>
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</head>
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<body>
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<div class="node">
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<a name="Classes"></a>
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<p>
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Next: <a rel="next" accesskey="n" href="Functions-for-C_002b_002b.html#Functions-for-C_002b_002b">Functions for C++</a>,
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Previous: <a rel="previous" accesskey="p" href="Namespaces.html#Namespaces">Namespaces</a>,
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Up: <a rel="up" accesskey="u" href="C-and-C_002b_002b-Trees.html#C-and-C_002b_002b-Trees">C and C++ Trees</a>
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<hr>
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</div>
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<h4 class="subsection">10.10.3 Classes</h4>
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<p><a name="index-class_002c-scope-2039"></a><a name="index-RECORD_005fTYPE-2040"></a><a name="index-UNION_005fTYPE-2041"></a><a name="index-CLASSTYPE_005fDECLARED_005fCLASS-2042"></a><a name="index-TYPE_005fBINFO-2043"></a><a name="index-BINFO_005fTYPE-2044"></a><a name="index-TYPE_005fFIELDS-2045"></a><a name="index-TYPE_005fVFIELD-2046"></a><a name="index-TYPE_005fMETHODS-2047"></a>
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Besides namespaces, the other high-level scoping construct in C++ is the
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class. (Throughout this manual the term <dfn>class</dfn> is used to mean the
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types referred to in the ANSI/ISO C++ Standard as classes; these include
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types defined with the <code>class</code>, <code>struct</code>, and <code>union</code>
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keywords.)
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<p>A class type is represented by either a <code>RECORD_TYPE</code> or a
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<code>UNION_TYPE</code>. A class declared with the <code>union</code> tag is
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represented by a <code>UNION_TYPE</code>, while classes declared with either
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the <code>struct</code> or the <code>class</code> tag are represented by
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<code>RECORD_TYPE</code>s. You can use the <code>CLASSTYPE_DECLARED_CLASS</code>
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macro to discern whether or not a particular type is a <code>class</code> as
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opposed to a <code>struct</code>. This macro will be true only for classes
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declared with the <code>class</code> tag.
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<p>Almost all non-function members are available on the <code>TYPE_FIELDS</code>
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list. Given one member, the next can be found by following the
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<code>TREE_CHAIN</code>. You should not depend in any way on the order in
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which fields appear on this list. All nodes on this list will be
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‘<samp><span class="samp">DECL</span></samp>’ nodes. A <code>FIELD_DECL</code> is used to represent a non-static
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data member, a <code>VAR_DECL</code> is used to represent a static data
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member, and a <code>TYPE_DECL</code> is used to represent a type. Note that
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the <code>CONST_DECL</code> for an enumeration constant will appear on this
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list, if the enumeration type was declared in the class. (Of course,
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the <code>TYPE_DECL</code> for the enumeration type will appear here as well.)
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There are no entries for base classes on this list. In particular,
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there is no <code>FIELD_DECL</code> for the “base-class portion” of an
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object.
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<p>The <code>TYPE_VFIELD</code> is a compiler-generated field used to point to
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virtual function tables. It may or may not appear on the
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<code>TYPE_FIELDS</code> list. However, back ends should handle the
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<code>TYPE_VFIELD</code> just like all the entries on the <code>TYPE_FIELDS</code>
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list.
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<p>The function members are available on the <code>TYPE_METHODS</code> list.
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Again, subsequent members are found by following the <code>TREE_CHAIN</code>
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field. If a function is overloaded, each of the overloaded functions
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appears; no <code>OVERLOAD</code> nodes appear on the <code>TYPE_METHODS</code>
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list. Implicitly declared functions (including default constructors,
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copy constructors, assignment operators, and destructors) will appear on
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this list as well.
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<p>Every class has an associated <dfn>binfo</dfn>, which can be obtained with
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<code>TYPE_BINFO</code>. Binfos are used to represent base-classes. The
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binfo given by <code>TYPE_BINFO</code> is the degenerate case, whereby every
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class is considered to be its own base-class. The base binfos for a
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particular binfo are held in a vector, whose length is obtained with
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<code>BINFO_N_BASE_BINFOS</code>. The base binfos themselves are obtained
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with <code>BINFO_BASE_BINFO</code> and <code>BINFO_BASE_ITERATE</code>. To add a
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new binfo, use <code>BINFO_BASE_APPEND</code>. The vector of base binfos can
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be obtained with <code>BINFO_BASE_BINFOS</code>, but normally you do not need
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to use that. The class type associated with a binfo is given by
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<code>BINFO_TYPE</code>. It is not always the case that <code>BINFO_TYPE
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(TYPE_BINFO (x))</code>, because of typedefs and qualified types. Neither is
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it the case that <code>TYPE_BINFO (BINFO_TYPE (y))</code> is the same binfo as
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<code>y</code>. The reason is that if <code>y</code> is a binfo representing a
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base-class <code>B</code> of a derived class <code>D</code>, then <code>BINFO_TYPE
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(y)</code> will be <code>B</code>, and <code>TYPE_BINFO (BINFO_TYPE (y))</code> will be
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<code>B</code> as its own base-class, rather than as a base-class of <code>D</code>.
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<p>The access to a base type can be found with <code>BINFO_BASE_ACCESS</code>.
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This will produce <code>access_public_node</code>, <code>access_private_node</code>
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or <code>access_protected_node</code>. If bases are always public,
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<code>BINFO_BASE_ACCESSES</code> may be <code>NULL</code>.
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<p><code>BINFO_VIRTUAL_P</code> is used to specify whether the binfo is inherited
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virtually or not. The other flags, <code>BINFO_MARKED_P</code> and
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<code>BINFO_FLAG_1</code> to <code>BINFO_FLAG_6</code> can be used for language
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specific use.
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<p>The following macros can be used on a tree node representing a class-type.
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<dl>
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<dt><code>LOCAL_CLASS_P</code><a name="index-LOCAL_005fCLASS_005fP-2048"></a><dd>This predicate holds if the class is local class <em>i.e.</em> declared
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inside a function body.
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<br><dt><code>TYPE_POLYMORPHIC_P</code><a name="index-TYPE_005fPOLYMORPHIC_005fP-2049"></a><dd>This predicate holds if the class has at least one virtual function
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(declared or inherited).
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<br><dt><code>TYPE_HAS_DEFAULT_CONSTRUCTOR</code><a name="index-TYPE_005fHAS_005fDEFAULT_005fCONSTRUCTOR-2050"></a><dd>This predicate holds whenever its argument represents a class-type with
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default constructor.
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<br><dt><code>CLASSTYPE_HAS_MUTABLE</code><a name="index-CLASSTYPE_005fHAS_005fMUTABLE-2051"></a><dt><code>TYPE_HAS_MUTABLE_P</code><a name="index-TYPE_005fHAS_005fMUTABLE_005fP-2052"></a><dd>These predicates hold for a class-type having a mutable data member.
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<br><dt><code>CLASSTYPE_NON_POD_P</code><a name="index-CLASSTYPE_005fNON_005fPOD_005fP-2053"></a><dd>This predicate holds only for class-types that are not PODs.
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<br><dt><code>TYPE_HAS_NEW_OPERATOR</code><a name="index-TYPE_005fHAS_005fNEW_005fOPERATOR-2054"></a><dd>This predicate holds for a class-type that defines
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<code>operator new</code>.
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<br><dt><code>TYPE_HAS_ARRAY_NEW_OPERATOR</code><a name="index-TYPE_005fHAS_005fARRAY_005fNEW_005fOPERATOR-2055"></a><dd>This predicate holds for a class-type for which
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<code>operator new[]</code> is defined.
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<br><dt><code>TYPE_OVERLOADS_CALL_EXPR</code><a name="index-TYPE_005fOVERLOADS_005fCALL_005fEXPR-2056"></a><dd>This predicate holds for class-type for which the function call
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<code>operator()</code> is overloaded.
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<br><dt><code>TYPE_OVERLOADS_ARRAY_REF</code><a name="index-TYPE_005fOVERLOADS_005fARRAY_005fREF-2057"></a><dd>This predicate holds for a class-type that overloads
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<code>operator[]</code>
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<br><dt><code>TYPE_OVERLOADS_ARROW</code><a name="index-TYPE_005fOVERLOADS_005fARROW-2058"></a><dd>This predicate holds for a class-type for which <code>operator-></code> is
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overloaded.
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</dl>
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</body></html>
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