QDeepCopy(3qt)

📦 version 3.3.8b, in fedora 43, fedora 44

💖 QDeepCopy 💖

okay bestie, gather round, because we're talking about QDeepCopy from the Qt 3 era (the manual page is literally called qdeepcopy.3qt, iykyk) — it's a template class and it's here to make sure that... well, the NAME section is famously a little cliffhanger that just ends mid-sentence. We'll get to that. 🫶

✨ NAME ✨

QDeepCopy — Template class which ensures that

(yes, that's genuinely where the original sentence stops. iconic. no notes. 💀)

🌸 SYNOPSIS 🌸

okay so literally every single function in this class is reentrant when Qt is built with thread support.</p>

(that </p> is just... there. it lives there now. we respect it.)

#include <qdeepcopy.h>

👑 Public Members 👑

QDeepCopy ()
QDeepCopy ( const T & t )
QDeepCopy<T> & operator= ( const T & t )
operator T ()

🦋 DESCRIPTION 🦋

so the whole vibe of QDeepCopy is this: it's a template class that makes implicitly shared and explicitly shared classes reference unique data. periodt.

Normally, shared copies point at the same data — that's the whole optimization, less memory, maximum speed, slay. In the example below, s1, s2, s3, s4 and s5 all share data.

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

Now QDeepCopy can be used several ways to make sure an object references unique, unshared data. In this next one, 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;

And in this one, 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. bestie that's on you, not on Qt. 🫡

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 DOCUMENTATION 💅

QDeepCopy::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 🌈

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. (so nobody wrote this, it just materialized. main character energy fr fr.)

🙈 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). 📝

and that's the whole page, bestie — brought to you by Trolltech AS, dated 2 February 2007, filed under QDeepCopy(3qt). go forth and deep copy responsibly, mwah 💋🌸

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