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137 lines
7.0 KiB
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<title>Simple Classes - STABS</title>
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<meta name="description" content="STABS">
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<link rel="up" href="Cplusplus.html#Cplusplus" title="Cplusplus">
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<link rel="prev" href="Basic-Cplusplus-Types.html#Basic-Cplusplus-Types" title="Basic Cplusplus Types">
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<!--
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Copyright (C) 1992-2019 Free Software Foundation, Inc.
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Contributed by Cygnus Support. Written by Julia Menapace, Jim Kingdon,
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and David MacKenzie.
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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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<body>
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<div class="node">
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<a name="Simple-Classes"></a>
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<p>
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Next: <a rel="next" accesskey="n" href="Class-Instance.html#Class-Instance">Class Instance</a>,
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Previous: <a rel="previous" accesskey="p" href="Basic-Cplusplus-Types.html#Basic-Cplusplus-Types">Basic Cplusplus Types</a>,
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Up: <a rel="up" accesskey="u" href="Cplusplus.html#Cplusplus">Cplusplus</a>
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<hr>
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</div>
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<h3 class="section">8.4 Simple Class Definition</h3>
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<p>The stabs describing C<tt>++</tt> language features are an extension of the
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stabs describing C. Stabs representing C<tt>++</tt> class types elaborate
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extensively on the stab format used to describe structure types in C.
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Stabs representing class type variables look just like stabs
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representing C language variables.
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<p>Consider the following very simple class definition.
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<pre class="example"> class baseA {
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public:
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int Adat;
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int Ameth(int in, char other);
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};
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</pre>
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<p>The class <code>baseA</code> is represented by two stabs. The first stab describes
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the class as a structure type. The second stab describes a structure
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tag of the class type. Both stabs are of stab type <code>N_LSYM</code>. Since the
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stab is not located between an <code>N_FUN</code> and an <code>N_LBRAC</code> stab this indicates
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that the class is defined at file scope. If it were, then the <code>N_LSYM</code>
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would signify a local variable.
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<p>A stab describing a C<tt>++</tt> class type is similar in format to a stab
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describing a C struct, with each class member shown as a field in the
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structure. The part of the struct format describing fields is
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expanded to include extra information relevant to C<tt>++</tt> class members.
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In addition, if the class has multiple base classes or virtual
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functions the struct format outside of the field parts is also
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augmented.
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<p>In this simple example the field part of the C<tt>++</tt> class stab
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representing member data looks just like the field part of a C struct
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stab. The section on protections describes how its format is
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sometimes extended for member data.
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<p>The field part of a C<tt>++</tt> class stab representing a member function
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differs substantially from the field part of a C struct stab. It
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still begins with ‘<samp><span class="samp">name:</span></samp>’ but then goes on to define a new type number
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for the member function, describe its return type, its argument types,
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its protection level, any qualifiers applied to the method definition,
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and whether the method is virtual or not. If the method is virtual
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then the method description goes on to give the vtable index of the
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method, and the type number of the first base class defining the
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method.
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<p>When the field name is a method name it is followed by two colons rather
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than one. This is followed by a new type definition for the method.
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This is a number followed by an equal sign and the type of the method.
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Normally this will be a type declared using the ‘<samp><span class="samp">#</span></samp>’ type
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descriptor; see <a href="Method-Type-Descriptor.html#Method-Type-Descriptor">Method Type Descriptor</a>; static member functions
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are declared using the ‘<samp><span class="samp">f</span></samp>’ type descriptor instead; see
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<a href="Function-Types.html#Function-Types">Function Types</a>.
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<p>The format of an overloaded operator method name differs from that of
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other methods. It is ‘<samp><span class="samp">op$::</span><var>operator-name</var><span class="samp">.</span></samp>’ where
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<var>operator-name</var> is the operator name such as ‘<samp><span class="samp">+</span></samp>’ or ‘<samp><span class="samp">+=</span></samp>’.
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The name ends with a period, and any characters except the period can
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occur in the <var>operator-name</var> string.
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<p>The next part of the method description represents the arguments to the
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method, preceded by a colon and ending with a semi-colon. The types of
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the arguments are expressed in the same way argument types are expressed
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in C<tt>++</tt> name mangling. In this example an <code>int</code> and a <code>char</code>
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map to ‘<samp><span class="samp">ic</span></samp>’.
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<p>This is followed by a number, a letter, and an asterisk or period,
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followed by another semicolon. The number indicates the protections
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that apply to the member function. Here the 2 means public. The
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letter encodes any qualifier applied to the method definition. In
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this case, ‘<samp><span class="samp">A</span></samp>’ means that it is a normal function definition. The dot
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shows that the method is not virtual. The sections that follow
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elaborate further on these fields and describe the additional
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information present for virtual methods.
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<pre class="display"> .stabs "class_name:sym_desc(type)type_def(20)=type_desc(struct)struct_bytes(4)
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field_name(Adat):type(int),bit_offset(0),field_bits(32);
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method_name(Ameth)::type_def(21)=type_desc(method)return_type(int);
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:arg_types(int char);
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protection(public)qualifier(normal)virtual(no);;"
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N_LSYM,NIL,NIL,NIL
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</pre>
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<pre class="smallexample"> .stabs "baseA:t20=s4Adat:1,0,32;Ameth::21=##1;:ic;2A.;;",128,0,0,0
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.stabs "class_name:sym_desc(struct tag)",N_LSYM,NIL,NIL,NIL
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.stabs "baseA:T20",128,0,0,0
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</pre>
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</body></html>
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