Qfile qt mac os

Qt Documentation

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macOS (previously known as OS X or Mac OS X) is Apple’s operating system for the Mac line of computers. It’s a UNIX platform, based on the Darwin kernel, and behaves largely similar to other UNIX-like platforms. The main difference is that X11 is not used as the windowing system. Instead, macOS uses its own native windowing system that is accessible through the Cocoa API.

To download and install Qt for macOS, follow the instructions on the Getting Started with Qt page.

Supported Versions

When talking about version support on macOS, it’s important to distinguish between the build environment; the platform you’re building on or with, and the target platforms; the platforms you are building for. The following macOS versions are supported.

Target Platform	Architecture	Build Environment
macOS 10.13, macOS 10.14, macOS 10.15, macOS 11	x86_64 and x86_64h	Xcode 11 or Xcode 12 (11 SDK)

Build Environment

The build environment on macOS is defined entirely by the Xcode version used to build your application. Xcode contains both a toolchain (compiler, linker, and other tools), and a macOS platform-SDK (headers and libraries). Together these define how your application is built.

Note: The version of macOS that you are running Xcode on does not matter. As long as Apple ships a given Xcode version that runs on your operating system, the build environment will be defined by that Xcode version.

Xcode can be downloaded from Apple’s developer website (including older versions of Xcode). Once installed, choosing an Xcode installation is done using the xcode-select tool.

You can inspect the globally selected Xcode installation using the same tool.

The xcrun command can then be used to find a particular tool in the toolchain.

or show the platform SDK path used when building.

Target Platforms

Building for macOS utilizes a technique called weak linking that allows you to build your application against the headers and libraries of the latest platform SDK, while still allowing your application to be deployed to macOS versions lower than the SDK version. When the binary is run on a macOS version lower than the SDK it was built with, Qt will check at runtime whether or not a platform feature is available before utilizing it.

In theory this would allow running your application on every single macOS version released, but for practical (and technical) reasons there is a lower limit to this range, known as the deployment target of your application. If the binary is launched on a macOS version below the deployment target macOS or Qt will give an error message and the application will not run.

Qt expresses the deployment target via the QMAKE_MACOSX_DEPLOYMENT_TARGET qmake variable, which has a default value set via the makespec for macOS. You should not need to change this default, but if needed you can increase it in your project file:

Note: You should not lower the deployment target beyond the default value set by Qt. Doing so will likely lead to crashes at runtime if the binary is then deployed to a macOS version lower than what Qt expected to run on.

By always building against the latest available platform SDK, you ensure that Qt can take advantage of new features introduced in recent versions of macOS.

For more information about SDK-based development on macOS, see Apple’s developer documentation.

Opting out of macOS behavior changes

One caveat to using the latest Xcode version and SDK to build your application is that macOS’s system frameworks will sometimes decide whether or not to enable behavior changes based on the SDK you built your application with.

For example, when dark-mode was introduced in macOS 10.14 Mojave, macOS would only treat applications built against the 10.14 SDK as supporting dark-mode, and would leave applications built against earlier SDKs with the default light mode look. This technique allows Apple to ensure that binaries built long before the new SDK and operating system was released will still continue to run without regressions on new macOS releases.

A consequence of this is that if Qt has problems dealing with some of these macOS features (dark-mode, layer-backed views), the only way to opt out of them is building with an earlier SDK (the 10.13 SDK, available through Xcode 9). This is a last-resort solution, and should only be applied if your application has no other ways of working around the problem.

Architectures

By default, Qt is built for x86_64. To build for x86_64h (Haswell). use the QMAKE_APPLE_DEVICE_ARCHS qmake variable. This is selectable at configure time:

QMAKE_APPLE_DEVICE_ARCHS can also be specified as a space-delimited list in order to build for multiple architectures simultaneously:

Additional Command-Line Options

On the command-line, applications can be built using qmake and make . Optionally, qmake can generate project files for Xcode with -spec macx-xcode . If you are using the binary package, qmake generates Xcode projects by default; use -spec macx-gcc to generate makefiles. For example:

Configuring with -spec macx-xcode generates an Xcode project file from project.pro. With qmake you do not have to worry about rules for Qt’s preprocessors (moc and uic) since qmake automatically handles them and ensures that everything necessary is linked into your application.

Qt does not entirely interact with the development environment (for example plugins to set a file to «mocable» from within the Xcode user interface).

The result of the build process is an application bundle, which is a directory structure that contains the actual application executable. The application can be launched by double-clicking it in Finder, or by referring directly to its executable from the command line, for example, myApp.app/Contents/MacOS/myApp .

If you wish to have a command-line tool that does not use the GUI for example, moc , uic or ls , you can tell qmake to disable bundle creation from the CONFIG variable in the project file:

Deploying Applications on macOS

macOS applications are typically deployed as self-contained application bundles. The application bundle contains the application executable as well as dependencies such as the Qt libraries, plugins, translations and other resources you may need. Third party libraries like Qt are normally not installed system-wide; each application provides its own copy.

A common way to distribute applications is to provide a compressed disk image (.dmg file) that the user can mount in Finder. The deployment tool, macdeployqt (available from the macOS installers), can be used to create the self-contained bundles, and optionally also create a .dmg archive. Applications can also be distributed through the Mac App Store. Qt 5 aims to stay within the app store sandbox rules. macdeployqt (bin/macdeployqt) can be used as a starting point for app store deployment.

Note: For selling applications in the macOS App Store, special rules apply. In order to pass validation, the application must verify the existence of a valid receipt before executing any code. Since this is a copy protection mechanism, steps should be taken to avoid common patterns and obfuscate the code that validates the receipt as much as possible. Thus, this cannot be automated by Qt, but requires some platform-specific code written specifically for the application itself. More information can be found in Apple’s documentation.

macOS Issues

The page below covers specific issues and recommendations for creating macOS applications.

Where to Go from Here

We invite you to explore the rest of Qt. We prepared overviews to help you decide which APIs to use and our examples demonstrate how to use our API.

• Qt Overviews — list of topics about application development
• Examples and Tutorials — code samples and tutorials
• Qt Reference Pages — a listing of C++ and QML APIs

Qt’s vibrant and active community site, http://qt.io houses a wiki, a forum, and additional learning guides and presentations.

В© 2021 The Qt Company Ltd. Documentation contributions included herein are the copyrights of their respective owners. The documentation provided herein is licensed under the terms of the GNU Free Documentation License version 1.3 as published by the Free Software Foundation. Qt and respective logos are trademarks of The Qt Company Ltd. in Finland and/or other countries worldwide. All other trademarks are property of their respective owners.

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Qt Documentation

Contents

The QFile class provides an interface for reading from and writing to files. More.

Note: All functions in this class are reentrant.

Public Types

Public Functions

Header:	#include
qmake:	QT += core
Inherits:	QFileDevice
Inherited By:

QFile(const QString &name, QObject *parent)
QFile(QObject *parent)
QFile(const QString &name)
QFile()
virtual	QFile()
bool	copy(const QString &newName)
bool	exists() const
bool	link(const QString &linkName)
bool	moveToTrash()
bool	open(FILE *fh, QIODevice::OpenMode mode, QFileDevice::FileHandleFlags handleFlags = DontCloseHandle)
bool	open(int fd, QIODevice::OpenMode mode, QFileDevice::FileHandleFlags handleFlags = DontCloseHandle)
bool	remove()
bool	rename(const QString &newName)
void	setFileName(const QString &name)
QString	symLinkTarget() const

Reimplemented Public Functions

virtual QString	fileName() const override
virtual bool	open(QIODevice::OpenMode mode) override
virtual QFileDevice::Permissions	permissions() const override
virtual bool	resize(qint64 sz) override
virtual bool	setPermissions(QFileDevice::Permissions permissions) override
virtual qint64	size() const override

Static Public Members

bool	copy(const QString &fileName, const QString &newName)
QString	decodeName(const QByteArray &localFileName)
QString	decodeName(const char *localFileName)
QByteArray	encodeName(const QString &fileName)
bool	exists(const QString &fileName)
bool	link(const QString &fileName, const QString &linkName)
bool	moveToTrash(const QString &fileName, QString *pathInTrash = nullptr)
QFileDevice::Permissions	permissions(const QString &fileName)
bool	remove(const QString &fileName)
bool	rename(const QString &oldName, const QString &newName)
bool	resize(const QString &fileName, qint64 sz)
bool	setPermissions(const QString &fileName, QFileDevice::Permissions permissions)
QString	symLinkTarget(const QString &fileName)

Detailed Description

QFile is an I/O device for reading and writing text and binary files and resources. A QFile may be used by itself or, more conveniently, with a QTextStream or QDataStream.

The file name is usually passed in the constructor, but it can be set at any time using setFileName(). QFile expects the file separator to be ‘/’ regardless of operating system. The use of other separators (e.g., ‘\’) is not supported.

You can check for a file’s existence using exists(), and remove a file using remove(). (More advanced file system related operations are provided by QFileInfo and QDir.)

The file is opened with open(), closed with close(), and flushed with flush(). Data is usually read and written using QDataStream or QTextStream, but you can also call the QIODevice-inherited functions read(), readLine(), readAll(), write(). QFile also inherits getChar(), putChar(), and ungetChar(), which work one character at a time.

The size of the file is returned by size(). You can get the current file position using pos(), or move to a new file position using seek(). If you’ve reached the end of the file, atEnd() returns true .

Reading Files Directly

The following example reads a text file line by line:

The QIODevice::Text flag passed to open() tells Qt to convert Windows-style line terminators («\r\n») into C++-style terminators («\n»). By default, QFile assumes binary, i.e. it doesn’t perform any conversion on the bytes stored in the file.

Using Streams to Read Files

The next example uses QTextStream to read a text file line by line:

QTextStream takes care of converting the 8-bit data stored on disk into a 16-bit Unicode QString. By default, it assumes that the user system’s local 8-bit encoding is used (e.g., UTF-8 on most unix based operating systems; see QTextCodec::codecForLocale() for details). This can be changed using QTextStream::setCodec().

To write text, we can use operator >() to read it back. See the class documentation for details.

When you use QFile, QFileInfo, and QDir to access the file system with Qt, you can use Unicode file names. On Unix, these file names are converted to an 8-bit encoding. If you want to use standard C++ APIs ( or ) or platform-specific APIs to access files instead of QFile, you can use the encodeName() and decodeName() functions to convert between Unicode file names and 8-bit file names.

On Unix, there are some special system files (e.g. in /proc ) for which size() will always return 0, yet you may still be able to read more data from such a file; the data is generated in direct response to you calling read(). In this case, however, you cannot use atEnd() to determine if there is more data to read (since atEnd() will return true for a file that claims to have size 0). Instead, you should either call readAll(), or call read() or readLine() repeatedly until no more data can be read. The next example uses QTextStream to read /proc/modules line by line:

Signals

Unlike other QIODevice implementations, such as QTcpSocket, QFile does not emit the aboutToClose(), bytesWritten(), or readyRead() signals. This implementation detail means that QFile is not suitable for reading and writing certain types of files, such as device files on Unix platforms.

Platform Specific Issues

File permissions are handled differently on Unix-like systems and Windows. In a non writable directory on Unix-like systems, files cannot be created. This is not always the case on Windows, where, for instance, the ‘My Documents’ directory usually is not writable, but it is still possible to create files in it.

Qt’s understanding of file permissions is limited, which affects especially the QFile::setPermissions() function. On Windows, Qt will set only the legacy read-only flag, and that only when none of the Write* flags are passed. Qt does not manipulate access control lists (ACLs), which makes this function mostly useless for NTFS volumes. It may still be of use for USB sticks that use VFAT file systems. POSIX ACLs are not manipulated, either.

Member Type Documentation

typedef QFile:: DecoderFn

This is a typedef for a pointer to a function with the following signature:

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