QDeepCopy(3qt)QDeepCopy(3qt)NAMEQDeepCopy - Template class which ensures that
SYNOPSIS
All the functions in this class are reentrant when Qt is built with
thread support.</p>
#include <qdeepcopy.h>
Public Members
QDeepCopy ()
QDeepCopy ( const T & t )
QDeepCopy<T> & operator= ( const T & t )
operator T ()
DESCRIPTION
The QDeepCopy class is a template class which ensures that implicitly
shared and explicitly shared classes reference unique data.
Normally, shared copies reference the same data to optimize memory use
and for maximum speed. In the example below, s1, s2, s3, s4 and s5
share data.
// all 5 strings share the same data
QString s1 = "abcd";
QString s2 = s1;
QString s3 = s2;
QString s4 = s3;
QString s5 = s2;
QDeepCopy can be used several ways to ensure that an object references
unique, unshared data. In the example below, s1, s2 and s5 share data,
while neither s3 nor s4 share data.
// s1, s2 and s5 share the same data, neither s3 nor s4 are shared
QString s1 = "abcd";
QString s2 = s1;
QDeepCopy<QString> s3 = s2; // s3 is a deep copy of s2
QString s4 = s3; // s4 is a deep copy of s3
QString s5 = s2;
In the example below, s1, s2 and s5 share data, and s3 and s4 share
data.
// s1, s2 and s5 share the same data, s3 and s4 share the same data
QString s1 = "abcd";
QString s2 = s1;
QString s3 = QDeepCopy<QString>( s2 ); // s3 is a deep copy of s2
QString s4 = s3; // s4 is a shallow copy of s3
QString s5 = s2;
QDeepCopy can also provide safety in multithreaded applications that
use shared classes. In the example below, the variable global_string is
used safely since the data contained in global_string is always a deep
copy. This ensures that all threads get a unique copy of the data, and
that any assignments to global_string will result in a deep copy.
QDeepCopy<QString> global_string; // global string data
QMutex global_mutex; // mutex to protext global_string
...
void setGlobalString( const QString &str )
{
global_mutex.lock();
global_string = str; // global_string is a deep copy of str
global_mutex.unlock();
}
...
void MyThread::run()
{
global_mutex.lock();
QString str = global_string; // str is a deep copy of global_string
global_mutex.unlock();
// process the string data
...
// update global_string
setGlobalString( str );
}
Warning: It is the application developer's responsibility to protect
the object shared across multiple threads.
The examples above use QString, which is an implicitly shared class.
The behavior of QDeepCopy is the same when using explicitly shared
classes like QByteArray.
Currently, QDeepCopy works with the following classes:
QMemArray (including subclasses like QByteArray and QCString)
QMap
QString
QValueList (including subclasses like QStringList and QValueStack)
QValueVector
See also Thread Support in Qt, Implicitly and Explicitly Shared
Classes, and Non-GUI Classes.
MEMBER FUNCTION DOCUMENTATIONQDeepCopy::QDeepCopy ()
Constructs an empty instance of type T.
QDeepCopy::QDeepCopy ( const T & t )
Constructs a deep copy of t.
QDeepCopy::operator T ()
Returns a deep copy of the encapsulated data.
QDeepCopy<;T> & QDeepCopy::operator= ( const T & t )
Assigns a deep copy of t.
SEE ALSO
http://doc.trolltech.com/qdeepcopy.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
(qdeepcopy.3qt) and the Qt version (3.3.8).
Trolltech AS 2 February 2007 QDeepCopy(3qt)
