×
UNIX.COM Login
Username:
Password:  
Show Password






👤


CentOS 7.0 - man page for qlibrary (centos section 3qt)

Linux & Unix Commands - Search Man Pages
Man Page or Keyword Search:
man
Select Man Page Set:
apropos Keyword Search (sections above)


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)
Unix & Linux Commands & Man Pages : ©2000 - 2018 Unix and Linux Forums


All times are GMT -4. The time now is 10:46 AM.

Unix & Linux Forums Content Copyright©1993-2018. All Rights Reserved.