1QLibrary(3qt)                                                    QLibrary(3qt)
2
3
4

NAME

6       QLibrary - Wrapper for handling shared libraries
7

SYNOPSIS

9       All the functions in this class are reentrant when Qt is built with
10       thread support.</p>
11
12       #include <qlibrary.h>
13
14   Public Members
15       QLibrary ( const QString & filename )
16       virtual ~QLibrary ()
17       void * resolve ( const char * symb )
18       bool load ()
19       virtual bool unload ()
20       bool isLoaded () const
21       bool autoUnload () const
22       void setAutoUnload ( bool enabled )
23       QString library () const
24
25   Static Public Members
26       void * resolve ( const QString & filename, const char * symb )
27

DESCRIPTION

29       The QLibrary class provides a wrapper for handling shared libraries.
30
31       An instance of a QLibrary object can handle a single shared library and
32       provide access to the functionality in the library in a platform
33       independent way. If the library is a component server, QLibrary
34       provides access to the exported component and can directly query this
35       component for interfaces.
36
37       QLibrary ensures that the shared library is loaded and stays in memory
38       whilst it is in use. QLibrary can also unload the library on
39       destruction and release unused resources.
40
41       A typical use of QLibrary is to resolve an exported symbol in a shared
42       object, and to call the function that this symbol represents. This is
43       called "explicit linking" in contrast to" implicit linking", which is
44       done by the link step in the build process when linking an executable
45       against a library.
46
47       The following code snippet loads a library, resolves the symbol"
48       mysymbol", and calls the function if everything succeeded. If something
49       went wrong, e.g. the library file does not exist or the symbol is not
50       defined, the function pointer will be 0 and won't be called. When the
51       QLibrary object is destroyed the library will be unloaded, making all
52       references to memory allocated in the library invalid.
53
54           typedef void (*MyPrototype)();
55           MyPrototype myFunction;
56           QLibrary myLib( "mylib" );
57           myFunction = (MyPrototype) myLib.resolve( "mysymbol" );
58           if ( myFunction ) {
59               myFunction();
60           }
61
62       See also Plugins.
63

MEMBER FUNCTION DOCUMENTATION

QLibrary::QLibrary ( const QString & filename )

66       Creates a QLibrary object for the shared library filename. The library
67       will be unloaded in the destructor.
68
69       Note that filename does not need to include the (platform specific)
70       file extension, so calling
71
72           QLibrary lib( "mylib" );
73       is equivalent to calling
74
75           QLibrary lib( "mylib.dll" );
76       on Windows, and
77
78           QLibrary lib( "libmylib.so" );
79       on Unix. Specifying the extension is not recommended, since doing so
80       introduces a platform dependency.
81
82       If filename does not include a path, the library loader will look for
83       the file in the platform specific search paths.
84
85       See also load(), unload(), and setAutoUnload().
86

QLibrary::~QLibrary () [virtual]

88       Deletes the QLibrary object.
89
90       The library will be unloaded if autoUnload() is TRUE (the default),
91       otherwise it stays in memory until the application exits.
92
93       See also unload() and setAutoUnload().
94

bool QLibrary::autoUnload () const

96       Returns TRUE if the library will be automatically unloaded when this
97       wrapper object is destructed; otherwise returns FALSE. The default is
98       TRUE.
99
100       See also setAutoUnload().
101

bool QLibrary::isLoaded () const

103       Returns TRUE if the library is loaded; otherwise returns FALSE.
104
105       See also unload().
106

QString QLibrary::library () const

108       Returns the filename of the shared library this QLibrary object
109       handles, including the platform specific file extension.
110
111       For example:
112
113           QLibrary lib( "mylib" );
114           QString str = lib.library();
115       will set str to "mylib.dll" on Windows, and "libmylib.so" on Linux.
116

bool QLibrary::load ()

118       Loads the library. Since resolve() always calls this function before
119       resolving any symbols it is not necessary to call it explicitly. In
120       some situations you might want the library loaded in advance, in which
121       case you would use this function.
122
123       On Darwin and Mac OS X this function uses code from dlcompat, part of
124       the OpenDarwin project.
125
126       Copyright (c) 2002 Jorge Acereda and Peter O'Gorman
127
128       Permission is hereby granted, free of charge, to any person obtaining a
129       copy of this software and associated documentation files (the"
130       Software"), to deal in the Software without restriction, including
131       without limitation the rights to use, copy, modify, merge, publish,
132       distribute, sublicense, and/or sell copies of the Software, and to
133       permit persons to whom the Software is furnished to do so, subject to
134       the following conditions:
135
136       The above copyright notice and this permission notice shall be included
137       in all copies or substantial portions of the Software.
138
139       THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
140       OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
141       MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
142       IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY
143       CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,
144       TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
145       SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
146

void * QLibrary::resolve ( const char * symb )

148       Returns the address of the exported symbol symb. The library is loaded
149       if necessary. The function returns 0 if the symbol could not be
150       resolved or the library could not be loaded.
151
152           typedef int (*avgProc)( int, int );
153           avgProc avg = (avgProc) library->resolve( "avg" );
154           if ( avg )
155               return avg( 5, 8 );
156           else
157               return -1;
158
159       The symbol must be exported as a C-function from the library. This
160       requires the extern "C" notation if the library is compiled with a C++
161       compiler. On Windows you also have to explicitly export the function
162       from the DLL using the __declspec(dllexport) compiler directive.
163
164           extern "C" MY_EXPORT_MACRO int avg(int a, int b)
165           {
166               return (a + b) / 2;
167           }
168
169       with MY_EXPORT defined as
170
171           #ifdef Q_WS_WIN
172           # define MY_EXPORT __declspec(dllexport)
173           #else
174           # define MY_EXPORT
175           #endif
176
177       On Darwin and Mac OS X this function uses code from dlcompat, part of
178       the OpenDarwin project.
179
180       Copyright (c) 2002 Jorge Acereda and Peter O'Gorman
181
182       Permission is hereby granted, free of charge, to any person obtaining a
183       copy of this software and associated documentation files (the"
184       Software"), to deal in the Software without restriction, including
185       without limitation the rights to use, copy, modify, merge, publish,
186       distribute, sublicense, and/or sell copies of the Software, and to
187       permit persons to whom the Software is furnished to do so, subject to
188       the following conditions:
189
190       The above copyright notice and this permission notice shall be included
191       in all copies or substantial portions of the Software.
192
193       THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
194       OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
195       MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
196       IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY
197       CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,
198       TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
199       SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
200

void * QLibrary::resolve ( const QString & filename, const char * symb )

202       [static]
203       This is an overloaded member function, provided for convenience. It
204       behaves essentially like the above function.
205
206       Loads the library filename and returns the address of the exported
207       symbol symb. Note that like the constructor, filename does not need to
208       include the (platform specific) file extension. The library remains
209       loaded until the process exits.
210
211       The function returns 0 if the symbol could not be resolved or the
212       library could not be loaded.
213
214       This function is useful only if you want to resolve a single symbol,
215       e.g. a function pointer from a specific library once:
216
217           typedef void (*FunctionType)();
218           static FunctionType *ptrFunction = 0;
219           static bool triedResolve = FALSE;
220           if ( !ptrFunction && !triedResolve )
221               ptrFunction = QLibrary::resolve( "mylib", "mysymb" );
222           if ( ptrFunction )
223               ptrFunction();
224           else
225               ...
226
227       If you want to resolve multiple symbols, use a QLibrary object and call
228       the non-static version of resolve().
229
230       See also
231

void QLibrary::setAutoUnload ( bool enabled )

233       If enabled is TRUE (the default), the wrapper object is set to
234       automatically unload the library upon destruction. If enabled is FALSE,
235       the wrapper object is not unloaded unless you explicitly call unload().
236
237       See also autoUnload().
238

bool QLibrary::unload () [virtual]

240       Unloads the library and returns TRUE if the library could be unloaded;
241       otherwise returns FALSE.
242
243       This function is called by the destructor if autoUnload() is enabled.
244
245       See also resolve().
246
247

SEE ALSO

249       http://doc.trolltech.com/qlibrary.html
250       http://www.trolltech.com/faq/tech.html
251
253       Copyright 1992-2007 Trolltech ASA, http://www.trolltech.com.  See the
254       license file included in the distribution for a complete license
255       statement.
256

AUTHOR

258       Generated automatically from the source code.
259

BUGS

261       If you find a bug in Qt, please report it as described in
262       http://doc.trolltech.com/bughowto.html.  Good bug reports help us to
263       help you. Thank you.
264
265       The definitive Qt documentation is provided in HTML format; it is
266       located at $QTDIR/doc/html and can be read using Qt Assistant or with a
267       web browser. This man page is provided as a convenience for those users
268       who prefer man pages, although this format is not officially supported
269       by Trolltech.
270
271       If you find errors in this manual page, please report them to qt-
272       bugs@trolltech.com.  Please include the name of the manual page
273       (qlibrary.3qt) and the Qt version (3.3.8).
274
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276
277Trolltech AS                    2 February 2007                  QLibrary(3qt)
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