QTemporaryFile Class Reference

The QTemporaryFile class is an I/O device that operates on temporary files. More...

 #include <QTemporaryFile>

Inherits: QFile.

Note: All functions in this class are reentrant.

Public Functions

QTemporaryFile ()
QTemporaryFile ( const QString & templateName )
QTemporaryFile ( QObject * parent )
QTemporaryFile ( const QString & templateName, QObject * parent )
~QTemporaryFile ()
bool autoRemove () const
QString fileName () const
QString fileTemplate () const
bool open ()
void setAutoRemove ( bool b )
void setFileTemplate ( const QString & name )
  • 29 public functions inherited from QFile
  • 33 public functions inherited from QIODevice
  • 29 public functions inherited from QObject

Static Public Members

QTemporaryFile * createLocalFile ( QFile & file )
QTemporaryFile * createLocalFile ( const QString & fileName )
  • 14 static public members inherited from QFile
  • 7 static public members inherited from QObject

Reimplemented Protected Functions

virtual bool open ( OpenMode flags )
  • 3 protected functions inherited from QFile
  • 5 protected functions inherited from QIODevice
  • 8 protected functions inherited from QObject

Additional Inherited Members

  • 1 property inherited from QObject
  • 1 public slot inherited from QObject
  • 4 signals inherited from QIODevice
  • 1 signal inherited from QObject
  • 3 protected functions inherited from QFile
  • 5 protected functions inherited from QIODevice
  • 8 protected functions inherited from QObject

Detailed Description

The QTemporaryFile class is an I/O device that operates on temporary files.

QTemporaryFile is used to create unique temporary files safely. The file itself is created by calling open(). The name of the temporary file is guaranteed to be unique (i.e., you are guaranteed to not overwrite an existing file), and the file will subsequently be removed upon destruction of the QTemporaryFile object. This is an important technique that avoids data corruption for applications that store data in temporary files. The file name is either auto-generated, or created based on a template, which is passed to QTemporaryFile's constructor.

Example:

     // Within a function/method...

     QTemporaryFile file;
     if (file.open()) {
         // file.fileName() returns the unique file name
     }

     // The QTemporaryFile destructor removes the temporary file
     // as it goes out of scope.

Reopening a QTemporaryFile after calling close() is safe. For as long as the QTemporaryFile object itself is not destroyed, the unique temporary file will exist and be kept open internally by QTemporaryFile.

The file name of the temporary file can be found by calling fileName(). Note that this is only defined after the file is first opened; the function returns an empty string before this.

A temporary file will have some static part of the name and some part that is calculated to be unique. The default filename qt_temp will be placed into the temporary path as returned by QDir::tempPath(). If you specify your own filename, a relative file path will not be placed in the temporary directory by default, but be relative to the current working directory.

Specified filenames can contain the following template XXXXXX (six upper case "X" characters), which will be replaced by the auto-generated portion of the filename. Note that the template is case sensitive. If the template is not present in the filename, QTemporaryFile appends the generated part to the filename given.

See also QDir::tempPath() and QFile.

Member Function Documentation

QTemporaryFile::QTemporaryFile ()

Constructs a QTemporaryFile in QDir::tempPath(), using the file template "qt_temp.XXXXXX". The file is stored in the system's temporary directory.

See also setFileTemplate() and QDir::tempPath().

QTemporaryFile::QTemporaryFile ( const QString & templateName )

Constructs a QTemporaryFile with a template filename of templateName. Upon opening the temporary file this will be used to create a unique filename.

If the templateName does not contain XXXXXX it will automatically be appended and used as the dynamic portion of the filename.

If templateName is a relative path, the path will be relative to the current working directory. You can use QDir::tempPath() to construct templateName if you want use the system's temporary directory.

See also open() and fileTemplate().

QTemporaryFile::QTemporaryFile ( QObject * parent )

Constructs a QTemporaryFile (with the given parent) in QDir::tempPath(), using the file template "qt_temp.XXXXXX".

See also setFileTemplate().

QTemporaryFile::QTemporaryFile ( const QString & templateName, QObject * parent )

Constructs a QTemporaryFile with a template filename of templateName and the specified parent. Upon opening the temporary file this will be used to create a unique filename.

If the templateName does not contain XXXXXX it will automatically be appended and used as the dynamic portion of the filename.

If templateName is a relative path, the path will be relative to the current working directory. You can use QDir::tempPath() to construct templateName if you want use the system's temporary directory.

See also open() and fileTemplate().

QTemporaryFile::~QTemporaryFile ()

Destroys the temporary file object, the file is automatically closed if necessary and if in auto remove mode it will automatically delete the file.

See also autoRemove().

bool QTemporaryFile::autoRemove () const

Returns true if the QTemporaryFile is in auto remove mode. Auto-remove mode will automatically delete the filename from disk upon destruction. This makes it very easy to create your QTemporaryFile object on the stack, fill it with data, read from it, and finally on function return it will automatically clean up after itself.

Auto-remove is on by default.

See also setAutoRemove() and remove().

QTemporaryFile * QTemporaryFile::createLocalFile ( QFile & file ) [static]

If file is not on a local disk, a temporary file is created on a local disk, file is copied into the temporary local file, and a pointer to the temporary local file is returned. If file is already on a local disk, a copy is not created and 0 is returned.

QTemporaryFile * QTemporaryFile::createLocalFile ( const QString & fileName ) [static]

This is an overloaded function.

Works on the given fileName rather than an existing QFile object.

QString QTemporaryFile::fileName () const

Returns the complete unique filename backing the QTemporaryFile object. This string is null before the QTemporaryFile is opened, afterwards it will contain the fileTemplate() plus additional characters to make it unique.

See also fileTemplate().

QString QTemporaryFile::fileTemplate () const

Returns the set file template. The default file template will be called qt_temp and be placed in QDir::tempPath().

See also setFileTemplate().

bool QTemporaryFile::open ()

A QTemporaryFile will always be opened in QIODevice::ReadWrite mode, this allows easy access to the data in the file. This function will return true upon success and will set the fileName() to the unique filename used.

See also fileName().

bool QTemporaryFile::open ( OpenMode flags ) [virtual protected]

Reimplemented from QIODevice::open().

Creates a unique file name for the temporary file, and opens it. You can get the unique name later by calling fileName(). The file is guaranteed to have been created by this function (i.e., it has never existed before).

void QTemporaryFile::setAutoRemove ( bool b )

Sets the QTemporaryFile into auto-remove mode if b is true.

Auto-remove is on by default.

See also autoRemove() and remove().

void QTemporaryFile::setFileTemplate ( const QString & name )

Sets the static portion of the file name to name. If the file template ends in XXXXXX that will automatically be replaced with the unique part of the filename, otherwise a filename will be determined automatically based on the static portion specified.

If name contains a relative file path, the path will be relative to the current working directory. You can use QDir::tempPath() to construct name if you want use the system's temporary directory.

See also fileTemplate().

Notes provided by the Qt Community

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