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1.1 root 1: @node ANSI
2: @chapter @sc{gnu} C++ Conformance to @sc{ansi} C++
3:
4: These changes in the @sc{gnu} C++ compiler were made to comply more
5: closely with the @sc{ansi} base document, @cite{The Annotated C++
6: Reference Manual} (the @sc{arm}). Further reducing the divergences from
7: @sc{ansi} C++ is a continued goal of the @sc{gnu} C++ Renovation
8: Project.
9:
1.1.1.2 ! root 10: @b{Section 3.4}, @i{Start and Termination}. It is now invalid to take
1.1 root 11: the address of the function @samp{main()}.
12:
13: @b{Section 4.8}, @i{Pointers to Members}. The compiler produces
14: an error for trying to convert between a pointer to a member and the type
15: @samp{void *}.
16:
17: @b{Section 5.2.5}, @i{Increment and Decrement}. It is an error to use
18: the increment and decrement operators on an enumerated type.
19:
20: @b{Section 5.3.2}, @i{Sizeof}. Doing @code{sizeof} on a function is now
21: an error.
22:
23: @b{Section 5.3.4}, @i{Delete}. The syntax of a @i{cast-expression} is
24: now more strictly controlled.
25:
26: @b{Section 7.1.1}, @i{Storage Class Specifiers}. Using the
27: @code{static} and @code{extern} specifiers can now only be applied to
28: names of objects, functions, and anonymous unions.
29:
30: @b{Section 7.1.1}, @i{Storage Class Specifiers}. The compiler no longer complains
31: about taking the address of a variable which has been declared to have @code{register}
32: storage.
33:
34: @b{Section 7.1.2}, @i{Function Specifiers}. The compiler produces an
35: error when the @code{inline} or @code{virtual} specifiers are
36: used on anything other than a function.
37:
38: @b{Section 8.3}, @i{Function Definitions}. It is now an error to shadow
39: a parameter name with a local variable; in the past, the compiler only
40: gave a warning in such a situation.
41:
42: @b{Section 8.4.1}, @i{Aggregates}. The rules concerning declaration of
43: an aggregate are now all checked in the @sc{gnu} C++ compiler; they
44: include having no private or protected members and no base classes.
45:
46: @b{Section 8.4.3}, @i{References}. Declaring an array of references is
47: now forbidden. Initializing a reference with an initializer list is
48: also considered an error.
49:
50: @b{Section 9.5}, @i{Unions}. Global anonymous unions must be declared
51: @code{static}.
52:
53: @b{Section 11.4}, @i{Friends}. Declaring a member to be a friend of a
54: type that has not yet been defined is an error.
55:
56: @b{Section 12.1}, @i{Constructors}. The compiler generates a
57: default copy constructor for a class if no constructor has been declared.
58:
59: @ignore
60: @b{Section 12.4}, @i{Destructors}. In accordance with the @sc{ansi} C++
61: draft standard working paper, a pure virtual destructor must now be
62: defined.
63: @end ignore
64:
65: @b{Section 12.6.2}, @i{Special Member Functions}. When using a
66: @i{mem-initializer} list, the compiler will now initialize class members
67: in declaration order, not in the order in which you specify them.
68: Also, the compiler enforces the rule that non-static @code{const}
69: and reference members must be initialized with a @i{mem-initializer}
70: list when their class does not have a constructor.
71:
72: @b{Section 12.8}, @i{Copying Class Objects}. The compiler generates
73: default copy constructors correctly, and supplies default assignment
74: operators compatible with user-defined ones.
75:
76: @b{Section 13.4}, @i{Overloaded Operators}. An overloaded operator may
77: no longer have default arguments.
78:
79: @b{Section 13.4.4}, @i{Function Call}. An overloaded @samp{operator ()}
80: must be a non-static member function.
81:
82: @b{Section 13.4.5}, @i{Subscripting}. An overloaded @samp{operator []}
83: must be a non-static member function.
84:
85: @b{Section 13.4.6}, @i{Class Member Access}. An overloaded @samp{operator ->}
86: must be a non-static member function.
87:
88: @b{Section 13.4.7}, @i{Increment and Decrement}. The compiler will now
89: make sure a postfix @samp{@w{operator ++}} or @samp{@w{operator --}} has an
90: @code{int} as its second argument.
91:
92:
93: @node Encoding
94: @chapter Name Encoding in @sc{gnu} C++
95:
96: @c FIXME!! rewrite name encoding section
97: @c ...to give complete rules rather than diffs from ARM.
98: @c To avoid plagiarism, invent some different way of structuring the
99: @c description of the rules than what ARM uses.
100:
101: @cindex mangling
102: @cindex name encoding
103: @cindex encoding information in names
104: In order to support its strong typing rules and the ability to provide
105: function overloading, the C++ programming language @dfn{encodes}
106: information about functions and objects, so that conflicts across object
107: files can be detected during linking. @footnote{This encoding is also
108: sometimes called, whimsically enough, @dfn{mangling}; the corresponding
109: decoding is sometimes called @dfn{demangling}.} These rules tend to be
110: unique to each individual implementation of C++.
111:
112: The scheme detailed in the commentary for 7.2.1 of @cite{The Annotated
113: Reference Manual} offers a description of a possible implementation
114: which happens to closely resemble the @code{cfront} compiler. The
115: design used in @sc{gnu} C++ differs from this model in a number of ways:
116:
117: @itemize @bullet
118: @item
119: In addition to the basic types @code{void}, @code{char}, @code{short},
120: @code{int}, @code{long}, @code{float}, @code{double}, and @code{long
121: double}, @sc{gnu} C++ supports two additional types: @code{wchar_t}, the wide
122: character type, and @code{long long} (if the host supports it). The
123: encodings for these are @samp{w} and @samp{x} respectively.
124:
125: @item
126: According to the @sc{arm}, qualified names (e.g., @samp{foo::bar::baz}) are
127: encoded with a leading @samp{Q}. Followed by the number of
128: qualifications (in this case, three) and the respective names, this
129: might be encoded as @samp{Q33foo3bar3baz}. @sc{gnu} C++ adds a leading
130: underscore to the list, producing @samp{_Q33foo3bar3baz}.
131:
132: @item
133: The operator @samp{*=} is encoded as @samp{__aml}, not @samp{__amu}, to
134: match the normal @samp{*} operator, which is encoded as @samp{__ml}.
135:
136: @c XXX left out ->(), __wr
137: @item
138: In addition to the normal operators, @sc{gnu} C++ also offers the minimum and
139: maximum operators @samp{>?} and @samp{<?}, encoded as @samp{__mx} and
140: @samp{__mn}, and the conditional operator @samp{?:}, encoded as @samp{__cn}.
141:
142: @cindex destructors, encoding of
143: @cindex constructors, encoding of
144: @item
145: Constructors are encoded as simply @samp{__@var{name}}, where @var{name}
146: is the encoded name (e.g., @code{3foo} for the @code{foo} class
147: constructor). Destructors are encoded as two leading underscores
148: separated by either a period or a dollar sign, depending on the
149: capabilities of the local host, followed by the encoded name. For
150: example, the destructor @samp{foo::~foo} is encoded as @samp{_$_3foo}.
151:
152: @item
153: Virtual tables are encoded with a prefix of @samp{_vt}, rather than
154: @samp{__vtbl}. The names of their classes are separated by dollar signs
155: (or periods), and not encoded as normal: the virtual table for
156: @code{foo} is @samp{__vt$foo}, and the table for @code{foo::bar} is
157: named @samp{__vt$foo$bar}.
158:
159: @item
160: Static members are encoded as a leading underscore, followed by the
161: encoded name of the class in which they appear, a separating dollar sign
162: or period, and finally the unencoded name of the variable. For example,
163: if the class @code{foo} contains a static member @samp{bar}, its
164: encoding would be @samp{_3foo$bar}.
165:
166: @item
167: @sc{gnu} C++ is not as aggressive as other compilers when it comes to always
168: generating @samp{Fv} for functions with no arguments. In particular,
169: the compiler does not add the sequence to conversion operators. The
170: function @samp{foo::bar()} is encoded as @samp{bar__3foo}, not
171: @samp{bar__3fooFv}.
172:
173: @item
174: The argument list for methods is not prefixed by a leading @samp{F}; it
175: is considered implied.
176:
177: @item
178: @sc{gnu} C++ approaches the task of saving space in encodings
179: differently from that noted in the @sc{arm}. It does use the
180: @samp{T@var{n}} and @samp{N@var{x}@var{y}} codes to signify copying the
181: @var{n}th argument's type, and making the next @var{x} arguments be the
182: type of the @var{y}th argument, respectively. However, the values for
183: @var{n} and @var{y} begin at zero with @sc{gnu} C++, whereas the
184: @sc{arm} describes them as starting at one. For the function @samp{foo
185: (bartype, bartype)}, @sc{gnu} C++ uses @samp{foo__7bartypeT0}, while
186: compilers following the @sc{arm} example generate @samp{foo__7bartypeT1}.
187:
188: @c Note it loses on `foo (int, int, int, int, int)'.
189: @item
190: @sc{gnu} C++ does not bother using the space-saving methods for types whose
191: encoding is a single character (like an integer, encoded as @samp{i}).
192: This is useful in the most common cases (two @code{int}s would result in
193: using three letters, instead of just @samp{ii}).
194: @end itemize
195:
196: @c @node Cfront
197: @c @chapter @code{cfront} Compared to @sc{gnu} C++
198: @c
199: @c
200: @c FIXME!! Fill in. Consider points in the following:
201: @c
202: @c @display
203: @c Date: Thu, 2 Jan 92 21:35:20 EST
204: @c From: raeburn@@cygnus.com
205: @c Message-Id: <9201030235.AA10999@@cambridge.cygnus.com>
206: @c To: mrs@@charlie.secs.csun.edu
207: @c Cc: g++@@cygnus.com
208: @c Subject: Re: ARM and GNU C++ incompatabilities
209: @c
210: @c Along with that, we should probably describe how g++ differs from
211: @c cfront, in ways that the users will notice. (E.g., cfront supposedly
212: @c allows "free (new char[10])"; does g++? How do the template
213: @c implementations differ? "New" placement syntax?)
214: @c @end display
215: @c
216: @c XXX For next revision.
217: @c
218: @c GNU C++:
219: @c * supports expanding inline functions in many situations,
220: @c including those which have static objects, use `for' statements,
221: @c and other situations. Part of this versatility is due to is
222: @c ability to not always generate temporaries for assignments.
223: @c * deliberately allows divide by 0 and mod 0, since [according
224: @c to Wilson] there are actually situations where you'd like to allow
225: @c such things. Note on most systems it will cause some sort of trap
226: @c or bus error. Cfront considers it an error.
227: @c * does [appear to] support nested classes within templates.
228: @c * conversion functions among baseclasses are all usable by
229: @c a class that's derived from all of those bases.
230: @c * sizeof works even when the class is defined within its ()'s
231: @c * conditional expressions work with member fns and pointers to
232: @c members.
233: @c * can handle non-trivial declarations of variables within switch
234: @c statements.
235: @c
236: @c Cfront:
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