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# QLibrary Class Reference

The QLibrary class provides a wrapper for handling shared libraries. More...

`#include <qlibrary.h>`

List of all member functions.

## Public Members

- enum Policy { Delayed, Immediately, Manual }
- QLibrary ( const QString & filename, Policy pol = Delayed )
- ~QLibrary ()
- void * resolve ( const char * symb )
- bool unload ( bool force = FALSE )
- bool isLoaded () const
- void setPolicy ( Policy pol )
- Policy policy () const
- QString library () const
- QRESULT queryInterface ( const QUuid & request, QUnknownInterface ** iface )

## Static Public Members

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

## Detailed Description

The QLibrary class provides a wrapper for handling shared libraries.

This class is temporarily copied from Qt 3.0.

## Member Type Documentation

### QLibrary::Policy

This enum type defines the various policies a QLibrary can have with respect to loading and unloading the shared library.

The policy can be:

- `QLibrary::Delayed` - The library get's loaded as soon as needed and unloaded in the destructor
- `QLibrary::Immediately` - The library is loaded immediately and unloaded in the destructor
- `QLibrary::Manual` - Like delayed, and library has to be unloaded manually

## Member Function Documentation

### QLibrary::QLibrary ( const QString & filename, Policy pol = Delayed )

Creates a QLibrary object for the shared library filename. The library get's loaded if pol is Immediately.

Note that filename does not need to include the (platform specific) file extension, so calling

      QLibrary lib( "mylib" );

would be equivalent to

      QLibrary lib( "mylib.dll" );

on Windows. But "mylib.dll" will obviously not work on other platforms.

See also setPolicy() and unload().

### QLibrary::~QLibrary ()

Deletes the QLibrary object. The library will be unloaded if the policy is not Manual.

See also unload() and setPolicy().

### bool QLibrary::isLoaded () const

Returns whether the library is loaded.

See also unload().

### QString QLibrary::library () const

Returns the filename of the shared library this QLibrary object handles, including the platform specific file extension.

      QLibrary lib( "mylib" );
      QString str = lib.library();

will set str to "mylib.dll" on Windows, and "libmylib.so" on Linux.

### Policy QLibrary::policy () const

Returns the current policy.

See also setPolicy().

### QRESULT QLibrary::queryInterface ( const QUuid & request, QUnknownInterface ** iface )

Forwards the query to the component and returns the result. request and iface are propagated to the component's queryInterface implementation.

The library gets loaded if necessary.

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

Returns the address of the exported symbol symb. The library gets loaded if necessary. The function returns NULL if the symbol could not be resolved, or if loading the library failed.

      typedef int (*addProc)( int, int );

      addProc add = (addProc) library->resolve( "add" );
      if ( add )
          return add( 5, 8 );
      else
          return 5 + 8;

See also queryInterface().

### 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 for the constructor, filename does not need to include the (platform specific) file extension. The library staying loaded until the process exits.

The function returns a null pointer if the symbol could not be resolved or if loading the library failed.

### void QLibrary::setPolicy ( Policy pol )

Sets the current policy to pol. The library is loaded if pol is set to Immediately.

### bool QLibrary::unload ( bool force = FALSE )

Releases the component and unloads the library when successful. Returns TRUE if the library could be unloaded, otherwise FALSE. If the component implements the QLibraryInterface, the cleanup() function of this interface will be called. The unloading will be cancelled if the subsequent call to canUnload() returns FALSE.

This function gets called automatically in the destructor if the policy is not Manual.

Warning: If force is set to TRUE, the library gets unloaded at any cost, which is in most cases a segmentation fault, so you should know what you're doing!

See also queryInterface() and resolve().

This file is part of the Qtopia , copyright © 1995-2002 Trolltech, all rights reserved.