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QLibrary(3qt)							 QLibrary(3qt)

NAME
       QLibrary - 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 DOCUMENTATION
QLibrary::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)
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