The QLibrary class loads shared libraries at runtime. More...

#include <qlibrary.h>

Inheritance diagram for QLibrary:

Collaboration diagram for QLibrary:

Public Types
enum	LoadHint { ResolveAllSymbolsHint = 0x01 , ExportExternalSymbolsHint = 0x02 , LoadArchiveMemberHint = 0x04 , PreventUnloadHint = 0x08 , DeepBindHint = 0x10 }

Public Member Functions
	QLibrary (QObject *parent=nullptr)

	QLibrary (const QString &fileName, QObject *parent=nullptr)

	QLibrary (const QString &fileName, int verNum, QObject *parent=nullptr)

	QLibrary (const QString &fileName, const QString &version, QObject *parent=nullptr)

	~QLibrary ()

QFunctionPointer	resolve (const char *symbol)

bool	load ()

bool	unload ()

bool	isLoaded () const

void	setFileName (const QString &fileName)

QString	fileName () const

void	setFileNameAndVersion (const QString &fileName, int verNum)

void	setFileNameAndVersion (const QString &fileName, const QString &version)

QString	errorString () const

void	setLoadHints (LoadHints hints)

LoadHints	loadHints () const

Public Member Functions inherited from QObject
Q_INVOKABLE	QObject (QObject *parent=nullptr)

virtual	~QObject ()

virtual bool	event (QEvent *event)

virtual bool	eventFilter (QObject watched, QEvent event)

QString	objectName () const

void	setObjectName (const QString &name)

QBindable< QString >	bindableObjectName ()

bool	isWidgetType () const

bool	isWindowType () const

bool	signalsBlocked () const noexcept

bool	blockSignals (bool b) noexcept

QThread *	thread () const

void	moveToThread (QThread *thread)

int	startTimer (int interval, Qt::TimerType timerType=Qt::CoarseTimer)

void	killTimer (int id)

template<typename T >
T	findChild (const QString &aName=QString(), Qt::FindChildOptions options=Qt::FindChildrenRecursively) const

template<typename T >
QList< T >	findChildren (const QString &aName, Qt::FindChildOptions options=Qt::FindChildrenRecursively) const

template<typename T >
QList< T >	findChildren (Qt::FindChildOptions options=Qt::FindChildrenRecursively) const

const QObjectList &	children () const

void	setParent (QObject *parent)

void	installEventFilter (QObject *filterObj)

void	removeEventFilter (QObject *obj)

QMetaObject::Connection	connect (const QObject sender, const char signal, const char *member, Qt::ConnectionType type=Qt::AutoConnection) const

bool	disconnect (const char signal=nullptr, const QObject receiver=nullptr, const char *member=nullptr) const

bool	disconnect (const QObject receiver, const char member=nullptr) const

void	dumpObjectTree () const

void	dumpObjectInfo () const

bool	setProperty (const char *name, const QVariant &value)

QVariant	property (const char *name) const

QList< QByteArray >	dynamicPropertyNames () const

QBindingStorage *	bindingStorage ()

const QBindingStorage *	bindingStorage () const

QObject *	parent () const

bool	inherits (const char *classname) const

Static Public Member Functions
static QFunctionPointer	resolve (const QString &fileName, const char *symbol)

static QFunctionPointer	resolve (const QString &fileName, int verNum, const char *symbol)

static QFunctionPointer	resolve (const QString &fileName, const QString &version, const char *symbol)

static bool	isLibrary (const QString &fileName)

Static Public Member Functions inherited from QObject
static QMetaObject::Connection	connect (const QObject sender, const char signal, const QObject receiver, const char member, Qt::ConnectionType=Qt::AutoConnection)

static QMetaObject::Connection	connect (const QObject sender, const QMetaMethod &signal, const QObject receiver, const QMetaMethod &method, Qt::ConnectionType type=Qt::AutoConnection)

template<typename Func1 , typename Func2 >
static QMetaObject::Connection	connect (const typename QtPrivate::FunctionPointer< Func1 >::Object sender, Func1 signal, const typename QtPrivate::FunctionPointer< Func2 >::Object receiver, Func2 slot, Qt::ConnectionType type=Qt::AutoConnection)

static QMetaObject::Connection ::type	connect (const typename QtPrivate::FunctionPointer< Func1 >::Object *sender, Func1 signal, Func2 slot)

static QMetaObject::Connection ::type	connect (const typename QtPrivate::FunctionPointer< Func1 >::Object sender, Func1 signal, const QObject context, Func2 slot, Qt::ConnectionType type=Qt::AutoConnection)

template<typename Func1 , typename Func2 >
static std::enable_if< QtPrivate::FunctionPointer< Func2 >::ArgumentCount==-1 &&!std::is_convertible_v< Func2, const char * >, QMetaObject::Connection >::type	connect (const typename QtPrivate::FunctionPointer< Func1 >::Object *sender, Func1 signal, Func2 slot)

template<typename Func1 , typename Func2 >
static std::enable_if< QtPrivate::FunctionPointer< Func2 >::ArgumentCount==-1 &&!std::is_convertible_v< Func2, const char * >, QMetaObject::Connection >::type	connect (const typename QtPrivate::FunctionPointer< Func1 >::Object sender, Func1 signal, const QObject context, Func2 slot, Qt::ConnectionType type=Qt::AutoConnection)

static bool	disconnect (const QObject sender, const char signal, const QObject receiver, const char member)

static bool	disconnect (const QObject sender, const QMetaMethod &signal, const QObject receiver, const QMetaMethod &member)

static bool	disconnect (const QMetaObject::Connection &)

template<typename Func1 , typename Func2 >
static bool	disconnect (const typename QtPrivate::FunctionPointer< Func1 >::Object sender, Func1 signal, const typename QtPrivate::FunctionPointer< Func2 >::Object receiver, Func2 slot)

template<typename Func1 >
static bool	disconnect (const typename QtPrivate::FunctionPointer< Func1 >::Object sender, Func1 signal, const QObject receiver, void **zero)

Properties
QString	fileName
	the file name of the library More...

LoadHints	loadHints
	Give the load() function some hints on how it should behave. More...

Properties inherited from QObject
QString	objectName
	the name of this object More...

Additional Inherited Members
Public Slots inherited from QObject
void	deleteLater ()

Signals inherited from QObject
void	destroyed (QObject *=nullptr)

void	objectNameChanged (const QString &objectName, QPrivateSignal)

Protected Member Functions inherited from QObject
QObject *	sender () const

int	senderSignalIndex () const

int	receivers (const char *signal) const

bool	isSignalConnected (const QMetaMethod &signal) const

virtual void	timerEvent (QTimerEvent *event)

virtual void	childEvent (QChildEvent *event)

virtual void	customEvent (QEvent *event)

virtual void	connectNotify (const QMetaMethod &signal)

virtual void	disconnectNotify (const QMetaMethod &signal)

	QObject (QObjectPrivate &dd, QObject *parent=nullptr)

Protected Attributes inherited from QObject
QScopedPointer< QObjectData >	d_ptr

Related Functions inherited from QObject
template< class T > T	qobject_cast (const QObject *object)

template< typename T > T	qFindChildqFindChildren (const QObject *obj, const QString &name)()

template< typename T > QList< T >	qFindChildrenqFindChildren (const QObject *obj, const QString &name)()

	QObjectList

Detailed Description

The QLibrary class loads shared libraries at runtime.

\inmodule QtCore \reentrant

An instance of a QLibrary object operates on a single shared object file (which we call a "library", but is also known as a "DLL"). A QLibrary provides access to the functionality in the library in a platform independent way. You can either pass a file name in the constructor, or set it explicitly with setFileName(). When loading the library, QLibrary searches in all the system-specific library locations (e.g. LD_LIBRARY_PATH on Unix), unless the file name has an absolute path.

If the file name is an absolute path then an attempt is made to load this path first. If the file cannot be found, QLibrary tries the name with different platform-specific file prefixes, like "lib" on Unix and Mac, and suffixes, like ".so" on Unix, ".dylib" on the Mac, or ".dll" on Windows.

If the file path is not absolute then QLibrary modifies the search order to try the system-specific prefixes and suffixes first, followed by the file path specified.

This makes it possible to specify shared libraries that are only identified by their basename (i.e. without their suffix), so the same code will work on different operating systems yet still minimise the number of attempts to find the library.

The most important functions are load() to dynamically load the library file, isLoaded() to check whether loading was successful, and resolve() to resolve a symbol in the library. The resolve() function implicitly tries to load the library if it has not been loaded yet. Multiple instances of QLibrary can be used to access the same physical library. Once loaded, libraries remain in memory until the application terminates. You can attempt to unload a library using unload(), but if other instances of QLibrary are using the same library, the call will fail, and unloading will only happen when every instance has called unload().

A typical use of QLibrary is to resolve an exported symbol in a library, and to call the C 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 goes wrong, e.g. the library file does not exist or the symbol is not defined, the function pointer will be \nullptr and won't be called.

The symbol must be exported as a C function from the library for resolve() to work. This means that the function must be wrapped in an {extern "C"} block if the library is compiled with a C++ compiler. On Windows, this also requires the use of a dllexport macro; see resolve() for the details of how this is done. For convenience, there is a static resolve() function which you can use if you just want to call a function in a library without explicitly loading the library first:

See also: QPluginLoader

Definition at line 52 of file qlibrary.h.

Member Enumeration Documentation

◆ LoadHint

enum QLibrary::LoadHint

This enum describes the possible hints that can be used to change the way libraries are handled when they are loaded. These values indicate how symbols are resolved when libraries are loaded, and are specified using the setLoadHints() function.

\value ResolveAllSymbolsHint Causes all symbols in a library to be resolved when it is loaded, not simply when resolve() is called. \value ExportExternalSymbolsHint Exports unresolved and external symbols in the library so that they can be resolved in other dynamically-loaded libraries loaded later. \value LoadArchiveMemberHint Allows the file name of the library to specify a particular object file within an archive file. If this hint is given, the filename of the library consists of a path, which is a reference to an archive file, followed by a reference to the archive member. \value PreventUnloadHint Prevents the library from being unloaded from the address space if close() is called. The library's static variables are not reinitialized if open() is called at a later time. \value DeepBindHint Instructs the linker to prefer definitions in the loaded library over exported definitions in the loading application when resolving external symbols in the loaded library. This option is only supported on Linux.

See also: loadHints

Enumerator
ResolveAllSymbolsHint
ExportExternalSymbolsHint
LoadArchiveMemberHint
PreventUnloadHint
DeepBindHint

Definition at line 58 of file qlibrary.h.

Constructor & Destructor Documentation

◆ QLibrary() [1/4]

QLibrary::QLibrary ( QObject * parent = nullptr )

explicit

Constructs a library with the given parent.

Definition at line 859 of file qlibrary.cpp.

◆ QLibrary() [2/4]

QLibrary::QLibrary	(	const QString &	fileName,
		QObject *	parent = `nullptr`
	)

explicit

Constructs a library object with the given parent that will load the library specified by fileName.

We recommend omitting the file's suffix in fileName, since QLibrary will automatically look for the file with the appropriate suffix in accordance with the platform, e.g. ".so" on Unix, ".dylib" on \macos and iOS, and ".dll" on Windows. (See \l{fileName}.)

Definition at line 873 of file qlibrary.cpp.

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◆ QLibrary() [3/4]

QLibrary::QLibrary	(	const QString &	fileName,
		int	verNum,
		QObject *	parent = `nullptr`
	)

explicit

Constructs a library object with the given parent that will load the library specified by fileName and major version number verNum. Currently, the version number is ignored on Windows.

We recommend omitting the file's suffix in fileName, since QLibrary will automatically look for the file with the appropriate suffix in accordance with the platform, e.g. ".so" on Unix, ".dylib" on \macos and iOS, and ".dll" on Windows. (See \l{fileName}.)

Definition at line 888 of file qlibrary.cpp.

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◆ QLibrary() [4/4]

QLibrary::QLibrary	(	const QString &	fileName,
		const QString &	version,
		QObject *	parent = `nullptr`
	)

explicit

Constructs a library object with the given parent that will load the library specified by fileName and full version number version. Currently, the version number is ignored on Windows.

We recommend omitting the file's suffix in fileName, since QLibrary will automatically look for the file with the appropriate suffix in accordance with the platform, e.g. ".so" on Unix, ".dylib" on \macos and iOS, and ".dll" on Windows. (See \l{fileName}.)

Definition at line 903 of file qlibrary.cpp.

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◆ ~QLibrary()

QLibrary::~QLibrary ( )

Destroys the QLibrary object.

Unless unload() was called explicitly, the library stays in memory until the application terminates.

See also: isLoaded(), unload()

Definition at line 917 of file qlibrary.cpp.

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Member Function Documentation

◆ errorString()

QString QLibrary::errorString ( ) const

Since: 4.2

Returns a text string with the description of the last error that occurred. Currently, errorString will only be set if load(), unload() or resolve() for some reason fails.

Definition at line 1097 of file qlibrary.cpp.

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◆ fileName()

QString QLibrary::fileName ( ) const

Definition at line 955 of file qlibrary.cpp.

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◆ isLibrary()

bool QLibrary::isLibrary ( const QString & fileName )

static

Returns true if fileName has a valid suffix for a loadable library; otherwise returns false.

\table \header

Platform
Valid suffixes \row
Windows
.dll, .DLL \row
Unix/Linux
.so \row
AIX
.a \row
HP-UX
.sl, .so (HP-UXi) \row
\macos and iOS
.dylib, .bundle, .so \endtable

Trailing versioning numbers on Unix are ignored.

Definition at line 626 of file qlibrary.cpp.

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◆ isLoaded()

bool QLibrary::isLoaded ( ) const

Returns true if the library is loaded; otherwise returns false.

See also: load()

Definition at line 850 of file qlibrary.cpp.

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◆ load()

bool QLibrary::load ( )

Loads the library and returns true if the library was loaded successfully; otherwise returns false. 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.

See also: unload()

Definition at line 810 of file qlibrary.cpp.

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◆ loadHints()

QLibrary::LoadHints QLibrary::loadHints ( ) const

Definition at line 1151 of file qlibrary.cpp.

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◆ resolve() [1/4]

QFunctionPointer QLibrary::resolve ( const char * symbol )

Returns the address of the exported symbol symbol. The library is loaded if necessary. The function returns \nullptr if the symbol could not be resolved or if the library could not be loaded.

Example:

The symbol must be exported as a C function from the library. This means that the function must be wrapped in an {extern "C"} if the library is compiled with a C++ compiler. On Windows you must also explicitly export the function from the DLL using the {__declspec(dllexport)} compiler directive, for example:

with MY_EXPORT defined as

Definition at line 1024 of file qlibrary.cpp.

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◆ resolve() [2/4]

QFunctionPointer QLibrary::resolve	(	const QString &	fileName,
		const char *	symbol
	)

static

This is an overloaded member function, provided for convenience. It differs from the above function only in what argument(s) it accepts.

Loads the library fileName and returns the address of the exported symbol symbol. Note that fileName should not include the platform-specific file suffix; (see \l{fileName}). The library remains loaded until the application exits.

The function returns \nullptr if the symbol could not be resolved or if the library could not be loaded.

See also: resolve()

Definition at line 1044 of file qlibrary.cpp.

◆ resolve() [3/4]

QFunctionPointer QLibrary::resolve	(	const QString &	fileName,
		const QString &	version,
		const char *	symbol
	)

static

This is an overloaded member function, provided for convenience. It differs from the above function only in what argument(s) it accepts.

Since: 4.4

Loads the library fileName with full version number version and returns the address of the exported symbol symbol. Note that fileName should not include the platform-specific file suffix; (see \l{fileName}). The library remains loaded until the application exits. version is ignored on Windows.

The function returns \nullptr if the symbol could not be resolved or if the library could not be loaded.

See also: resolve()

Definition at line 1085 of file qlibrary.cpp.

◆ resolve() [4/4]

QFunctionPointer QLibrary::resolve	(	const QString &	fileName,
		int	verNum,
		const char *	symbol
	)

static

This is an overloaded member function, provided for convenience. It differs from the above function only in what argument(s) it accepts.

Loads the library fileName with major version number verNum and returns the address of the exported symbol symbol. Note that fileName should not include the platform-specific file suffix; (see \l{fileName}). The library remains loaded until the application exits. verNum is ignored on Windows.

The function returns \nullptr if the symbol could not be resolved or if the library could not be loaded.

See also: resolve()

Definition at line 1064 of file qlibrary.cpp.

◆ setFileName()

void QLibrary::setFileName ( const QString & fileName )

Definition at line 944 of file qlibrary.cpp.

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◆ setFileNameAndVersion() [1/2]

void QLibrary::setFileNameAndVersion	(	const QString &	fileName,
		const QString &	version
	)

Since: 4.4

Sets the fileName property and full version number to fileName and version respectively. The version parameter is ignored on Windows.

See also: setFileName()

Definition at line 993 of file qlibrary.cpp.

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◆ setFileNameAndVersion() [2/2]

void QLibrary::setFileNameAndVersion	(	const QString &	fileName,
		int	versionNumber
	)

Sets the fileName property and major version number to fileName and versionNumber respectively. The versionNumber is ignored on Windows.

See also: setFileName()

Definition at line 973 of file qlibrary.cpp.

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◆ setLoadHints()

void QLibrary::setLoadHints ( LoadHints hints )

Definition at line 1142 of file qlibrary.cpp.

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◆ unload()

bool QLibrary::unload ( )

Unloads the library and returns true if the library could be unloaded; otherwise returns false.

This happens automatically on application termination, so you shouldn't normally need to call this function.

If other instances of QLibrary are using the same library, the call will fail, and unloading will only happen when every instance has called unload().

Note that on Mac OS X 10.3 (Panther), dynamic libraries cannot be unloaded.

See also: resolve(), load()

Definition at line 836 of file qlibrary.cpp.

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Property Documentation

◆ fileName

QLibrary::fileName

readwrite

the file name of the library

We recommend omitting the file's suffix in the file name, since QLibrary will automatically look for the file with the appropriate suffix (see isLibrary()).

When loading the library, QLibrary searches in all system-specific library locations (for example, LD_LIBRARY_PATH on Unix), unless the file name has an absolute path. After loading the library successfully, fileName() returns the fully-qualified file name of the library, including the full path to the library if one was given in the constructor or passed to setFileName().

For example, after successfully loading the "GL" library on Unix platforms, fileName() will return "libGL.so". If the file name was originally passed as "/usr/lib/libGL", fileName() will return "/usr/lib/libGL.so".

Definition at line 108 of file qlibrary.h.

◆ loadHints

QLibrary::loadHints

readwrite

Give the load() function some hints on how it should behave.

You can give some hints on how the symbols are resolved. Usually, the symbols are not resolved at load time, but resolved lazily, (that is, when resolve() is called). If you set the loadHints to ResolveAllSymbolsHint, then all symbols will be resolved at load time if the platform supports it.

Setting ExportExternalSymbolsHint will make the external symbols in the library available for resolution in subsequent loaded libraries.

If LoadArchiveMemberHint is set, the file name is composed of two components: A path which is a reference to an archive file followed by the second component which is the reference to the archive member. For instance, the fileName libGL.a(shr_64.o) will refer to the library shr_64.o in the archive file named libGL.a. This is only supported on the AIX platform.

The interpretation of the load hints is platform dependent, and if you use it you are probably making some assumptions on which platform you are compiling for, so use them only if you understand the consequences of them.

By default, none of these flags are set, so libraries will be loaded with lazy symbol resolution, and will not export external symbols for resolution in other dynamically-loaded libraries.

Note: Setting this property after the library has been loaded has no effect and loadHints() will not reflect those changes.; This property is shared among all QLibrary instances that refer to the same library.

Definition at line 108 of file qlibrary.h.

The documentation for this class was generated from the following files:

src/corelib/plugin/qlibrary.h
src/corelib/plugin/qlibrary.cpp

Public Types

Public Member Functions

Static Public Member Functions

Properties

Additional Inherited Members

Detailed Description

Member Enumeration Documentation

◆ LoadHint

Constructor & Destructor Documentation

◆ QLibrary() [1/4]

◆ QLibrary() [2/4]

◆ QLibrary() [3/4]

◆ QLibrary() [4/4]

◆ ~QLibrary()

Member Function Documentation

◆ errorString()

◆ fileName()

◆ isLibrary()

◆ isLoaded()

◆ load()

◆ loadHints()

◆ resolve() [1/4]

◆ resolve() [2/4]

◆ resolve() [3/4]

◆ resolve() [4/4]

◆ setFileName()

◆ setFileNameAndVersion() [1/2]

◆ setFileNameAndVersion() [2/2]

◆ setLoadHints()

◆ unload()

Property Documentation

◆ fileName

◆ loadHints