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RedHat 9 (Linux i386) - man page for qlibrary (redhat section 3qt)

QLibrary(3qt)									    QLibrary(3qt)

       QLibrary - Wrapper for handling shared libraries

       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 )

       The QLibrary class provides a wrapper for handling shared libraries.

       \group plugins

       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 = (MyProtoype) myLib.resolve( "mysymbol" );
	   if ( myFunction ) {

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

	   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

       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.

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 );
	       return -1;

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

       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 )

       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

       This function is called by the destructor if autoUnload() is enabled.

       See also resolve().

       http://doc.trolltech.com/qlibrary.html http://www.trolltech.com/faq/tech.html

       Copyright 1992-2001 Trolltech AS, http://www.trolltech.com.  See the license file included
       in the distribution for a complete license statement.

       Generated automatically from the source code.

       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 (3.1.1).

Trolltech AS				 9 December 2002			    QLibrary(3qt)

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