Contents

• Public Functions
• Detailed Description

Detailed Description

TheQ3DeepCopy 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 ands5 share data.

// all 5 strings share the same dataQString s1="abcd";QString s2= s1;QString s3= s2;QString s4= s3;QString s5= s2;

Q3DeepCopy can be used several ways to ensure that an object references unique, unshared data. In the example below,s1,s2 ands5 share data, while neithers3 nors4 share data.

// s1, s2 and s5 share the same data, neither s3 nor s4 are sharedQString s1="abcd";QString s2= s1;Q3DeepCopy<QString> s3= s2;// s3 is a deep copy of s2QString s4= s3;// s4 is a deep copy of s3QString s5= s2;

In the example below,s1,s2 ands5 share data, ands3 ands4 share data.

// s1, s2 and s5 share the same data, s3 and s4 share the same dataQString s1="abcd";QString s2= s1;QString s3=Q3DeepCopy<QString>( s2 );// s3 is a deep copy of s2QString s4= s3;// s4 is a shallow copy of s3QString s5= s2;

Q3DeepCopy can also provide safety in multithreaded applications that use shared classes. In the example below, the variableglobal_string is used safely since the data contained inglobal_string is always a deep copy. This ensures that all threads get a unique copy of the data, and that any assignments toglobal_string will result in a deep copy.

Q3DeepCopy<QString> global_string;// global string dataQMutex global_mutex;// mutex to protext global_string...void setGlobalString(constQString&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 useQString, which is an implicitly shared class. The behavior ofQ3DeepCopy is the same when using explicitly shared classes likeQByteArray.

Currently,Q3DeepCopy works with the following classes:

• QMemArray (including subclasses likeQByteArray andQCString)
• QMap
• QString
• QValueList (including subclasses likeQStringList and QValueStack)
• QValueVector

Member Function Documentation

Q3DeepCopy::Q3DeepCopy()

Constructs an empty instance of typeT.

Q3DeepCopy::Q3DeepCopy(constT & t)

Constructs a deep copy oft.

Q3DeepCopy::operator T()

Returns a deep copy of the encapsulated data.

Q3DeepCopy<T> & Q3DeepCopy::operator=(constT & t)

Assigns a deep copy oft.