原文链接：https://blog.csdn.net/cc321123123/article/details/41701611
QT5 中有一个Implicit Sharing的概念，叫做隐式共享，许多QT中许多C++类用隐式数据共享来减少copy带来的资源占用问题。
当作为参数传递时，隐式数据共享是安全和高效的，因为仅仅是指向数据的指针进行传递，而数据只在有函数对它进行改写是才进行复制。（copy on write）
QT的如下类均用到了这个机理，如果不希望进行隐式共享，则需要多加注意了。
QDBusPendingCall
The QDBusPendingCall class refers to one pending asynchronous call
QDBusUnixFileDescriptor
The QDBusUnixFileDescriptor class holds one Unix file descriptor.
QBitmap
The QBitmap class provides monochrome (1-bit depth) pixmaps.
QIcon
The QIcon class provides scalable icons in different modes and states.
QImage
The QImage class provides a hardware-independent image representation that allows direct access to the pixel data, and can be used as a paint device.
QPicture
The QPicture class is a paint device that records and replays QPainter commands.
QPixmap
The QPixmap class is an off-screen image representation that can be used as a paint device.
QCursor
The QCursor class provides a mouse cursor with an arbitrary shape.
QKeySequence
The QKeySequence class encapsulates a key sequence as used by shortcuts.
QPalette
The QPalette class contains color groups for each widget state.
QOpenGLDebugMessage
The QOpenGLDebugMessage class wraps an OpenGL debug message.
QBrush
The QBrush class defines the fill pattern of shapes drawn by QPainter.
QGradient
The QGradient class is used in combination with QBrush to specify gradient fills.
QPainterPath
The QPainterPath class provides a container for painting operations, enabling graphical shapes to be constructed and reused.
QPen
The QPen class defines how a QPainter should draw lines and outlines of shapes.
QPolygon
The QPolygon class provides a vector of points using integer precision.
QPolygonF
The QPolygonF class provides a vector of points using floating point precision.
QRegion
The QRegion class specifies a clip region for a painter.
QFont
The QFont class specifies a font used for drawing text.
QFontInfo
The QFontInfo class provides general information about fonts.
QFontMetrics
The QFontMetrics class provides font metrics information.
QFontMetricsF
The QFontMetricsF class provides font metrics information.
QGlyphRun
The QGlyphRun class provides direct access to the internal glyphs in a font.
QRawFont
The QRawFont class provides access to a single physical instance of a font.
QStaticText
The QStaticText class enables optimized drawing of text when the text and its layout is updated rarely.
QTextCursor
The QTextCursor class offers an API to access and modify QTextDocuments.
QTextDocumentFragment
The QTextDocumentFragment class represents a piece of formatted text from a QTextDocument.
QTextBlockFormat
The QTextBlockFormat class provides formatting information for blocks of text in a QTextDocument.
QTextCharFormat
The QTextCharFormat class provides formatting information for characters in a QTextDocument.
QTextFormat
The QTextFormat class provides formatting information for a QTextDocument.
QTextFrameFormat
The QTextFrameFormat class provides formatting information for frames in a QTextDocument.
QTextImageFormat
The QTextImageFormat class provides formatting information for images in a QTextDocument.
QTextListFormat
The QTextListFormat class provides formatting information for lists in a QTextDocument.
QTextTableCellFormat
The QTextTableCellFormat class provides formatting information for table cells in a QTextDocument.
QTextTableFormat
The QTextTableFormat class provides formatting information for tables in a QTextDocument.
QNetworkCacheMetaData
The QNetworkCacheMetaData class provides cache information.
QHttpPart
The QHttpPart class holds a body part to be used inside a HTTP multipart MIME message.
QNetworkCookie
The QNetworkCookie class holds one network cookie.
QNetworkRequest
The QNetworkRequest class holds a request to be sent with QNetworkAccessManager.
QNetworkConfiguration
The QNetworkConfiguration class provides an abstraction of one or more access point configurations.
QDnsDomainNameRecord
The QDnsDomainNameRecord class stores information about a domain name record.
QDnsHostAddressRecord
The QDnsHostAddressRecord class stores information about a host address record.
QDnsMailExchangeRecord
The QDnsMailExchangeRecord class stores information about a DNS MX record.
QDnsServiceRecord
The QDnsServiceRecord class stores information about a DNS SRV record.
QDnsTextRecord
The QDnsTextRecord class stores information about a DNS TXT record.
QNetworkAddressEntry
The QNetworkAddressEntry class stores one IP address supported by a network interface, along with its associated netmask and broadcast address.
QNetworkInterface
The QNetworkInterface class provides a listing of the host’s IP addresses and network interfaces.
QNetworkProxy
The QNetworkProxy class provides a network layer proxy.
QNetworkProxyQuery
The QNetworkProxyQuery class is used to query the proxy settings for a socket.
QSslCertificate
The QSslCertificate class provides a convenient API for an X509 certificate.
QSslCertificateExtension
The QSslCertificateExtension class provides an API for accessing the extensions of an X509 certificate.
QSslCipher
The QSslCipher class represents an SSL cryptographic cipher.
QSslConfiguration
The QSslConfiguration class holds the configuration and state of an SSL connection
QSslError
The QSslError class provides an SSL error.
QSslKey
The QSslKey class provides an interface for private and public keys.
QDebug
Output stream for debugging information
QDir
Access to directory structures and their contents
QFileInfo
System-independent file information
QProcessEnvironment
Holds the environment variables that can be passed to a program
QUrl
Convenient interface for working with URLs
QUrlQuery
Way to manipulate a key-value pairs in a URL’s query
QPersistentModelIndex
Used to locate data in a data model
QVariant
Acts like a union for the most common Qt data types
QMimeType
Describes types of file or data, represented by a MIME type string
QBitArray
Array of bits
QByteArray
Array of bytes
QCache
Template class that provides a cache
QCollator
Compares strings according to a localized collation algorithm
QCollatorSortKey
Can be used to speed up string collation
QCommandLineOption
Defines a possible command-line option
QContiguousCache
Template class that provides a contiguous cache
QDateTime
Date and time functions
QHash
Template class that provides a hash-table-based dictionary
QMultiHash
Convenience QHash subclass that provides multi-valued hashes
QLinkedList
Template class that provides linked lists
QList
Template class that provides lists
QLocale
Converts between numbers and their string representations in various languages
QMap
Template class that provides a red-black-tree-based dictionary
QMultiMap
Convenience QMap subclass that provides multi-valued maps
QQueue
Generic container that provides a queue
QRegExp
Pattern matching using regular expressions
QRegularExpression
Pattern matching using regular expressions
QRegularExpressionMatch
The results of a matching a QRegularExpression against a string
QRegularExpressionMatchIterator
Iterator on the results of a global match of a QRegularExpression object against a string
QSet
Template class that provides a hash-table-based set
QStack
Template class that provides a stack
QString
Unicode character string
QStringList
List of strings
QTextBoundaryFinder
Way of finding Unicode text boundaries in a string
QVector
Template class that provides a dynamic array
我昨天就一直被这个问题困扰着，因为
imageList.append(captureImage); //QList imageList; QImage captureImage; captureImage每隔一段时间刷新一次
imageList ，无论向imageList 中添加多少数据，imageList中的数据始终相同，并保持与最近一次captureImage中的数据一致。
后来我发现问题所在，QList中存放的应该是QImage对象的引用，每添加一次，只是添加了captureImage的引用，因此Qlist中的所有
元素都是指向captureImage的引用，因此都与最近一次captureImage中的数据一致。
要想调用imageList.append(captureImage); 时，每次的数据随着captureImage刷新，需要在调用之前，将captureImage的数据拷贝一份，
而简单的用QImage captureImg=captureImage；是实现不了拷贝的，因为这里QImage只做了浅拷贝，并不是我们想要的深拷贝。
为了实现我们的目的其实很简单只需在imageList.append(captureImage); 加上这个语句：captureImage.detach(); 然后再 QImage captureImg=captureImage;就可以了
具体请看：
Implicit Sharing in Detail
Implicit sharing automatically detaches the object from a shared block if the object is about to change and the reference count is greater than one. (This is often called copy-on-write or value semantics.)
An implicitly shared class has control of its internal data. In any member functions that modify its data, it automatically detaches before modifying the data. Notice, however, the special case with container iterators; see Implicit sharing iterator problem.
The QPen class, which uses implicit sharing, detaches from the shared data in all member functions that change the internal data.
Code fragment:
void QPen::setStyle(Qt::PenStyle style)
{
detach(); // detach from common data
d->style = style; // set the style member
}
void QPen::detach()
{
if (d->ref != 1) {
… // perform a deep copy
}
}