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stringutils.hxx
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1 /* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4 -*- */
2 /*
3  * Version: MPL 1.1 / GPLv3+ / LGPLv3+
4  *
5  * The contents of this file are subject to the Mozilla Public License Version
6  * 1.1 (the "License"); you may not use this file except in compliance with
7  * the License or as specified alternatively below. You may obtain a copy of
8  * the License at http://www.mozilla.org/MPL/
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10  * Software distributed under the License is distributed on an "AS IS" basis,
11  * WITHOUT WARRANTY OF ANY KIND, either express or implied. See the License
12  * for the specific language governing rights and limitations under the
13  * License.
14  *
15  * Major Contributor(s):
16  * [ Copyright (C) 2012 Lubos Lunak <l.lunak@suse.cz> (initial developer) ]
17  *
18  * All Rights Reserved.
19  *
20  * For minor contributions see the git repository.
21  *
22  * Alternatively, the contents of this file may be used under the terms of
23  * either the GNU General Public License Version 3 or later (the "GPLv3+"), or
24  * the GNU Lesser General Public License Version 3 or later (the "LGPLv3+"),
25  * in which case the provisions of the GPLv3+ or the LGPLv3+ are applicable
26  * instead of those above.
27  */
28 
29 #ifndef _RTL_STRINGUTILS_HXX_
30 #define _RTL_STRINGUTILS_HXX_
31 
32 #include "sal/config.h"
33 
34 // The unittest uses slightly different code to help check that the proper
35 // calls are made. The class is put into a different namespace to make
36 // sure the compiler generates a different (if generating also non-inline)
37 // copy of the function and does not merge them together. The class
38 // is "brought" into the proper rtl namespace by a typedef below.
39 #ifdef RTL_STRING_UNITTEST
40 #define rtl rtlunittest
41 #endif
42 
43 namespace rtl
44 {
45 
46 #ifdef RTL_STRING_UNITTEST
47 #undef rtl
48 #endif
49 namespace internal
50 {
51 /*
52 These templates use SFINAE (Substitution failure is not an error) to help distinguish the various
53 plain C string types: char*, const char*, char[N], const char[N], char[] and const char[].
54 There are 2 cases:
55 1) Only string literal (i.e. const char[N]) is wanted, not any of the others.
56  In this case it is necessary to distinguish between const char[N] and char[N], as the latter
57  would be automatically converted to the const variant, which is not wanted (not a string literal
58  with known size of the content). In this case ConstCharArrayDetector is used to ensure the function
59  is called only with const char[N] arguments. There's no other plain C string type overload.
60 2) All plain C string types are wanted, and const char[N] needs to be handled differently.
61  In this case const char[N] would match const char* argument type (not exactly sure why, but it's
62  consistent in all of gcc, clang and msvc). Using a template with a reference to const of the type
63  avoids this problem, and CharPtrDetector ensures that the function is called only with char pointer
64  arguments. The const in the argument is necessary to handle the case when something is explicitly
65  cast to const char*. Additionally (non-const) char[N] needs to be handled, but with the reference
66  being const, it would also match const char[N], so another overload with a reference to non-const
67  and NonConstCharArrayDetector are used to ensure the function is called only with (non-const) char[N].
68 Additionally, char[] and const char[] (i.e. size unknown) are rather tricky. Their usage with 'T&' would
69 mean it would be 'char(&)[]', which seems to be invalid. But gcc and clang somehow manage when it is
70 a template. while msvc complains about no conversion from char[] to char[1]. And the reference cannot
71 be avoided, because 'const char[]' as argument type would match also 'const char[N]'
72 So char[] and const char[] should always be used with their contents specified (which automatically
73 turns them into char[N] or const char[N]), or char* and const char* should be used.
74 */
75 struct Dummy {};
76 template< typename T1, typename T2 >
78 {
79 };
80 template< typename T >
81 struct CharPtrDetector< const char*, T >
82 {
83  typedef T Type;
84 };
85 template< typename T >
86 struct CharPtrDetector< char*, T >
87 {
88  typedef T Type;
89 };
90 
91 template< typename T1, typename T2 >
93 {
94 };
95 template< typename T, int N >
96 struct NonConstCharArrayDetector< char[ N ], T >
97 {
98  typedef T Type;
99 };
100 #ifdef RTL_STRING_UNITTEST
101 // never use, until all compilers handle this
102 template< typename T >
103 struct NonConstCharArrayDetector< char[], T >
104 {
105  typedef T Type;
106 };
107 template< typename T >
108 struct NonConstCharArrayDetector< const char[], T >
109 {
110  typedef T Type;
111 };
112 #endif
113 
114 template< typename T1, typename T2 >
116 {
117 };
118 template< int N, typename T >
119 struct ConstCharArrayDetector< const char[ N ], T >
120 {
121  typedef T Type;
122  static const int size = N;
123 };
124 
125 // this one is used to rule out only const char[N]
126 template< typename T >
128 {
129  typedef Dummy Type;
130 };
131 template< int N >
132 struct ExceptConstCharArrayDetector< const char[ N ] >
133 {
134 };
135 // this one is used to rule out only const char[N]
136 // (const will be brought in by 'const T&' in the function call)
137 // msvc needs const char[N] here (not sure whether gcc or msvc
138 // are right, it doesn't matter).
139 template< typename T >
141 {
142  typedef Dummy Type;
143 };
144 template< int N >
145 struct ExceptCharArrayDetector< char[ N ] >
146 {
147 };
148 template< int N >
149 struct ExceptCharArrayDetector< const char[ N ] >
150 {
151 };
152 
153 } /* Namespace */
154 
155 } /* Namespace */
156 
157 #endif /* _RTL_STRINGUTILS_HXX_ */
158 
159 /* vim:set shiftwidth=4 softtabstop=4 expandtab: */