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comparison lwlib/xt-wrappers.h @ 4528:726060ee587c g++-warning-removal-2008-10-28

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First draft of g++ 4.3 warning removal patch. Builds. *Needs ChangeLogs.*
author Stephen J. Turnbull <stephen@xemacs.org>
date Wed, 29 Oct 2008 04:06:33 +0900
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1 /* Wrappers for Xt functions and macros
2
3 Copyright (C) 2008 Free Software Foundation
4
5 This file is part of XEmacs.
6
7 XEmacs is free software; you can redistribute it and/or modify it
8 under the terms of the GNU General Public License as published by the
9 Free Software Foundation; either version 2, or (at your option) any
10 later version.
11
12 XEmacs is distributed in the hope that it will be useful, but WITHOUT
13 ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
14 FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
15 for more details.
16 You should have received a copy of the GNU General Public License
17 along with XEmacs; see the file COPYING. If not, write to
18 the Free Software Foundation, Inc., 59 Temple Place - Suite 330,
19 Boston, MA 02111-1307, USA. */
20
21 /* Synched up with: Not in FSF. */
22
23 /* Original author: Stephen J. Turnbull for 21.5.29 */
24
25 /* Generic utility macros, including coping with G++ whining.
26 Used in lwlib via lwlib.h and X consoles via console-x.h.
27
28 We would prefer to find another way to shut up G++. The issue is that
29 recent versions of the C++ standard deprecate implicit conversions
30 across function boundaries like
31
32 typedef char *String;
33 void foo (String string);
34 foo ("bar");
35
36 because "bar" should be allowed to be a read-only array of chars. But of
37 course lots of legacy code (== X11) declares things as char * and expects
38 to assign literal strings to them. Now, the typedef in the example is
39 important because in G++ 4.3.2 at least, this
40
41 void foo (const String string);
42 foo ("bar");
43
44 does not work as expected! G++ still warns about this construct. However,
45 if foo is declared
46
47 void foo (const char *string);
48
49 G++ does not complain. (#### There are two possibilities I can think of.
50 (a) G++ is buggy. (b) "const String" is interpreted as "char * const".)
51
52 The upshot is that to avoid warnings with Xt's String typedef, we need to
53 arrange to cast literal strings to String, rather than use "const String"
54 in declarations. (My <X11/Intrinsic.h> says that the actual internal
55 typedef used is _XtString, so that String can be #define'd to something
56 else for the purposes of C++. But that doesn't really help us much.)
57
58 It's not very satisfactory to do it this way -- it would be much better to
59 have const Strings where they make sense -- but it does eliminate a few
60 hundred warnings from the C++ build. And in any case we don't control the
61 many objects declared with String components in Intrinsic.h. The remaining
62 issues are the WEXTTEXT macro used in src/emacs.c, and Emacs.ad.h (where
63 instead of String we use const char * in src/event-Xt.c in the array that
64 #includes it).
65 */
66
67 #ifndef INCLUDED_xt_wrappers_h_
68 #define INCLUDED_xt_wrappers_h_
69
70 /* Wrap XtResource, with the same elements as arguments.
71 The cast to String shuts up G++ 4.3's whining about const char *.
72 The invocation of sizeof should be pretty safe, and the cast to XtPointer
73 surely is, since that's how that member of XtResource is declared. It
74 doesn't hide potential problems, because XtPointer is a "generic" type in
75 any case -- the actual object will have a different type, that will be
76 cast to XtPointer. */
77
78 #define Xt_RESOURCE(name,_class,intrepr,type,member,extrepr,value) \
79 { (String) name, (String) _class, (String) intrepr, sizeof(type), \
80 member, extrepr, (XtPointer) value }
81
82 /* Wrap XtSetArg, with the same arguments.
83 The cast to String shuts up G++ 4.3's whining about const char *. */
84
85 #define Xt_SET_ARG(al, resource, x) do { \
86 XtSetArg ((al), (String) (resource), (x)); \
87 } while (0)
88
89 /* Convenience macros for getting/setting one resource value. */
90
91 #define Xt_SET_VALUE(widget, resource, value) do { \
92 Arg al; \
93 Xt_SET_ARG (al, resource, value); \
94 XtSetValues (widget, &al, 1); \
95 } while (0)
96
97 #define Xt_GET_VALUE(widget, resource, location) do { \
98 Arg al; \
99 Xt_SET_ARG (al, resource, location); \
100 XtGetValues (widget, &al, 1); \
101 } while (0)
102
103 #endif /* INCLUDED_xt_wrappers_h_ */