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239 lines
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239 lines
11 KiB
HTML
4 years ago
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<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
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<html>
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<!-- Copyright (C) 1988-2018 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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software. Copies published by the Free Software Foundation raise
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funds for GNU development. -->
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<!-- Created by GNU Texinfo 6.4, http://www.gnu.org/software/texinfo/ -->
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<head>
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<title>Classes (GNU Compiler Collection (GCC) Internals)</title>
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<meta name="description" content="Classes (GNU Compiler Collection (GCC) Internals)">
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<meta name="keywords" content="Classes (GNU Compiler Collection (GCC) Internals)">
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<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
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<link href="index.html#Top" rel="start" title="Top">
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<link href="Option-Index.html#Option-Index" rel="index" title="Option Index">
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<link href="index.html#SEC_Contents" rel="contents" title="Table of Contents">
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<link href="C-and-C_002b_002b-Trees.html#C-and-C_002b_002b-Trees" rel="up" title="C and C++ Trees">
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<link href="Functions-for-C_002b_002b.html#Functions-for-C_002b_002b" rel="next" title="Functions for C++">
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<link href="Namespaces.html#Namespaces" rel="prev" title="Namespaces">
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<style type="text/css">
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a.summary-letter {text-decoration: none}
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</head>
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<body lang="en">
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<a name="Classes"></a>
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<div class="header">
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<p>
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Next: <a href="Functions-for-C_002b_002b.html#Functions-for-C_002b_002b" accesskey="n" rel="next">Functions for C++</a>, Previous: <a href="Namespaces.html#Namespaces" accesskey="p" rel="prev">Namespaces</a>, Up: <a href="C-and-C_002b_002b-Trees.html#C-and-C_002b_002b-Trees" accesskey="u" rel="up">C and C++ Trees</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Option-Index.html#Option-Index" title="Index" rel="index">Index</a>]</p>
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</div>
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<hr>
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<a name="Classes-1"></a>
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<h4 class="subsection">11.10.3 Classes</h4>
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<a name="index-class_002c-scope"></a>
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<a name="index-RECORD_005fTYPE-1"></a>
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<a name="index-UNION_005fTYPE-1"></a>
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<a name="index-CLASSTYPE_005fDECLARED_005fCLASS"></a>
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<a name="index-TYPE_005fBINFO"></a>
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<a name="index-BINFO_005fTYPE"></a>
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<a name="index-TYPE_005fFIELDS-2"></a>
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<a name="index-TYPE_005fVFIELD"></a>
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<p>Besides namespaces, the other high-level scoping construct in C++ is the
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class. (Throughout this manual the term <em>class</em> 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>
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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>
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<p>Almost all 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>DECL</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. If a function member is overloaded, each of the overloaded
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functions appears; no <code>OVERLOAD</code> nodes appear on the <code>TYPE_FIELDS</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>
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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>
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<p>Every class has an associated <em>binfo</em>, 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>
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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>
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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_FLAG_0</code> to
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<code>BINFO_FLAG_6</code>, can be used for language specific use.
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</p>
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<p>The following macros can be used on a tree node representing a class-type.
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</p>
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<dl compact="compact">
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<dt><code>LOCAL_CLASS_P</code>
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<a name="index-LOCAL_005fCLASS_005fP"></a>
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</dt>
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<dd><p>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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</p>
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</dd>
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<dt><code>TYPE_POLYMORPHIC_P</code>
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<a name="index-TYPE_005fPOLYMORPHIC_005fP"></a>
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</dt>
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<dd><p>This predicate holds if the class has at least one virtual function
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(declared or inherited).
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</p>
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</dd>
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<dt><code>TYPE_HAS_DEFAULT_CONSTRUCTOR</code>
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<a name="index-TYPE_005fHAS_005fDEFAULT_005fCONSTRUCTOR"></a>
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</dt>
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<dd><p>This predicate holds whenever its argument represents a class-type with
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default constructor.
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</p>
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</dd>
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<dt><code>CLASSTYPE_HAS_MUTABLE</code>
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<a name="index-CLASSTYPE_005fHAS_005fMUTABLE"></a>
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</dt>
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<dt><code>TYPE_HAS_MUTABLE_P</code>
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<a name="index-TYPE_005fHAS_005fMUTABLE_005fP"></a>
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</dt>
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<dd><p>These predicates hold for a class-type having a mutable data member.
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</p>
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</dd>
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<dt><code>CLASSTYPE_NON_POD_P</code>
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<a name="index-CLASSTYPE_005fNON_005fPOD_005fP"></a>
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</dt>
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<dd><p>This predicate holds only for class-types that are not PODs.
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</p>
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</dd>
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<dt><code>TYPE_HAS_NEW_OPERATOR</code>
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<a name="index-TYPE_005fHAS_005fNEW_005fOPERATOR"></a>
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</dt>
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<dd><p>This predicate holds for a class-type that defines
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<code>operator new</code>.
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</p>
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</dd>
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<dt><code>TYPE_HAS_ARRAY_NEW_OPERATOR</code>
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<a name="index-TYPE_005fHAS_005fARRAY_005fNEW_005fOPERATOR"></a>
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</dt>
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<dd><p>This predicate holds for a class-type for which
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<code>operator new[]</code> is defined.
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</p>
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</dd>
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<dt><code>TYPE_OVERLOADS_CALL_EXPR</code>
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<a name="index-TYPE_005fOVERLOADS_005fCALL_005fEXPR"></a>
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</dt>
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<dd><p>This predicate holds for class-type for which the function call
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<code>operator()</code> is overloaded.
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</p>
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</dd>
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<dt><code>TYPE_OVERLOADS_ARRAY_REF</code>
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<a name="index-TYPE_005fOVERLOADS_005fARRAY_005fREF"></a>
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</dt>
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<dd><p>This predicate holds for a class-type that overloads
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<code>operator[]</code>
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</p>
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</dd>
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<dt><code>TYPE_OVERLOADS_ARROW</code>
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<a name="index-TYPE_005fOVERLOADS_005fARROW"></a>
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</dt>
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<dd><p>This predicate holds for a class-type for which <code>operator-></code> is
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overloaded.
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</p>
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</dd>
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</dl>
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<hr>
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<div class="header">
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<p>
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Next: <a href="Functions-for-C_002b_002b.html#Functions-for-C_002b_002b" accesskey="n" rel="next">Functions for C++</a>, Previous: <a href="Namespaces.html#Namespaces" accesskey="p" rel="prev">Namespaces</a>, Up: <a href="C-and-C_002b_002b-Trees.html#C-and-C_002b_002b-Trees" accesskey="u" rel="up">C and C++ Trees</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Option-Index.html#Option-Index" title="Index" rel="index">Index</a>]</p>
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</div>
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</body>
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</html>
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