QLibrary(3qt)QLibrary(3qt)NAMEQLibrary - Wrapper for handling shared libraries
SYNOPSIS
All the functions in this class are reentrant when Qt is built with
thread support.</p>
#include <qlibrary.h>
Public Members
QLibrary ( const QString & filename )
virtual ~QLibrary ()
void * resolve ( const char * symb )
bool load ()
virtual bool unload ()
bool isLoaded () const
bool autoUnload () const
void setAutoUnload ( bool enabled )
QString library () const
Static Public Members
void * resolve ( const QString & filename, const char * symb )
DESCRIPTION
The QLibrary class provides a wrapper for handling shared libraries.
An instance of a QLibrary object can handle a single shared library and
provide access to the functionality in the library in a platform
independent way. If the library is a component server, QLibrary
provides access to the exported component and can directly query this
component for interfaces.
QLibrary ensures that the shared library is loaded and stays in memory
whilst it is in use. QLibrary can also unload the library on
destruction and release unused resources.
A typical use of QLibrary is to resolve an exported symbol in a shared
object, and to call the function that this symbol represents. This is
called "explicit linking" in contrast to" implicit linking", which is
done by the link step in the build process when linking an executable
against a library.
The following code snippet loads a library, resolves the symbol"
mysymbol", and calls the function if everything succeeded. If something
went wrong, e.g. the library file does not exist or the symbol is not
defined, the function pointer will be 0 and won't be called. When the
QLibrary object is destroyed the library will be unloaded, making all
references to memory allocated in the library invalid.
typedef void (*MyPrototype)();
MyPrototype myFunction;
QLibrary myLib( "mylib" );
myFunction = (MyPrototype) myLib.resolve( "mysymbol" );
if ( myFunction ) {
myFunction();
}
See also Plugins.
MEMBER FUNCTION DOCUMENTATIONQLibrary::QLibrary ( const QString & filename )
Creates a QLibrary object for the shared library filename. The library
will be unloaded in the destructor.
Note that filename does not need to include the (platform specific)
file extension, so calling
QLibrary lib( "mylib" );
is equivalent to calling
QLibrary lib( "mylib.dll" );
on Windows, and
QLibrary lib( "libmylib.so" );
on Unix. Specifying the extension is not recommended, since doing so
introduces a platform dependency.
If filename does not include a path, the library loader will look for
the file in the platform specific search paths.
See also load(), unload(), and setAutoUnload().
QLibrary::~QLibrary () [virtual]
Deletes the QLibrary object.
The library will be unloaded if autoUnload() is TRUE (the default),
otherwise it stays in memory until the application exits.
See also unload() and setAutoUnload().
bool QLibrary::autoUnload () const
Returns TRUE if the library will be automatically unloaded when this
wrapper object is destructed; otherwise returns FALSE. The default is
TRUE.
See also setAutoUnload().
bool QLibrary::isLoaded () const
Returns TRUE if the library is loaded; otherwise returns FALSE.
See also unload().
QString QLibrary::library () const
Returns the filename of the shared library this QLibrary object
handles, including the platform specific file extension.
For example:
QLibrary lib( "mylib" );
QString str = lib.library();
will set str to "mylib.dll" on Windows, and "libmylib.so" on Linux.
bool QLibrary::load ()
Loads the library. Since resolve() always calls this function before
resolving any symbols it is not necessary to call it explicitly. In
some situations you might want the library loaded in advance, in which
case you would use this function.
On Darwin and Mac OS X this function uses code from dlcompat, part of
the OpenDarwin project.
Copyright (c) 2002 Jorge Acereda and Peter O'Gorman
Permission is hereby granted, free of charge, to any person obtaining a
copy of this software and associated documentation files (the"
Software"), to deal in the Software without restriction, including
without limitation the rights to use, copy, modify, merge, publish,
distribute, sublicense, and/or sell copies of the Software, and to
permit persons to whom the Software is furnished to do so, subject to
the following conditions:
The above copyright notice and this permission notice shall be included
in all copies or substantial portions of the Software.
THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY
CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,
TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
void * QLibrary::resolve ( const char * symb )
Returns the address of the exported symbol symb. The library is loaded
if necessary. The function returns 0 if the symbol could not be
resolved or the library could not be loaded.
typedef int (*avgProc)( int, int );
avgProc avg = (avgProc) library->resolve( "avg" );
if ( avg )
return avg( 5, 8 );
else
return -1;
The symbol must be exported as a C-function from the library. This
requires the extern "C" notation if the library is compiled with a C++
compiler. On Windows you also have to explicitly export the function
from the DLL using the __declspec(dllexport) compiler directive.
extern "C" MY_EXPORT_MACRO int avg(int a, int b)
{
return (a + b) / 2;
}
with MY_EXPORT defined as
#ifdef Q_WS_WIN
# define MY_EXPORT __declspec(dllexport)
#else
# define MY_EXPORT
#endif
On Darwin and Mac OS X this function uses code from dlcompat, part of
the OpenDarwin project.
Copyright (c) 2002 Jorge Acereda and Peter O'Gorman
Permission is hereby granted, free of charge, to any person obtaining a
copy of this software and associated documentation files (the"
Software"), to deal in the Software without restriction, including
without limitation the rights to use, copy, modify, merge, publish,
distribute, sublicense, and/or sell copies of the Software, and to
permit persons to whom the Software is furnished to do so, subject to
the following conditions:
The above copyright notice and this permission notice shall be included
in all copies or substantial portions of the Software.
THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY
CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,
TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
void * QLibrary::resolve ( const QString & filename, const char * symb )
[static]
This is an overloaded member function, provided for convenience. It
behaves essentially like the above function.
Loads the library filename and returns the address of the exported
symbol symb. Note that like the constructor, filename does not need to
include the (platform specific) file extension. The library remains
loaded until the process exits.
The function returns 0 if the symbol could not be resolved or the
library could not be loaded.
This function is useful only if you want to resolve a single symbol,
e.g. a function pointer from a specific library once:
typedef void (*FunctionType)();
static FunctionType *ptrFunction = 0;
static bool triedResolve = FALSE;
if ( !ptrFunction && !triedResolve )
ptrFunction = QLibrary::resolve( "mylib", "mysymb" );
if ( ptrFunction )
ptrFunction();
else
...
If you want to resolve multiple symbols, use a QLibrary object and call
the non-static version of resolve().
See also
void QLibrary::setAutoUnload ( bool enabled )
If enabled is TRUE (the default), the wrapper object is set to
automatically unload the library upon destruction. If enabled is FALSE,
the wrapper object is not unloaded unless you explicitly call unload().
See also autoUnload().
bool QLibrary::unload () [virtual]
Unloads the library and returns TRUE if the library could be unloaded;
otherwise returns FALSE.
This function is called by the destructor if autoUnload() is enabled.
See also resolve().
SEE ALSO
http://doc.trolltech.com/qlibrary.html
http://www.trolltech.com/faq/tech.html
COPYRIGHT
Copyright 1992-2007 Trolltech ASA, http://www.trolltech.com. See the
license file included in the distribution for a complete license
statement.
AUTHOR
Generated automatically from the source code.
BUGS
If you find a bug in Qt, please report it as described in
http://doc.trolltech.com/bughowto.html. Good bug reports help us to
help you. Thank you.
The definitive Qt documentation is provided in HTML format; it is
located at $QTDIR/doc/html and can be read using Qt Assistant or with a
web browser. This man page is provided as a convenience for those users
who prefer man pages, although this format is not officially supported
by Trolltech.
If you find errors in this manual page, please report them to qt-
bugs@trolltech.com. Please include the name of the manual page
(qlibrary.3qt) and the Qt version (3.3.8).
Trolltech AS 2 February 2007 QLibrary(3qt)