- Qt 6.9
- Qt Core
- C++ Classes
- QTemporaryFile
- Qt 6.9.3 Reference Documentation

# QTemporaryFile Class

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

Header: | `#include <QTemporaryFile>`
CMake: | `find_package(Qt6 REQUIRED COMPONENTS Core)` `target_link_libraries(mytarget PRIVATE Qt6::Core)`
qmake: | `QT += core`
Inherits: | QFile

- List of all members, including inherited members
- QTemporaryFile is part of Input/Output and Networking.

Note: All functions in this class are reentrant.

## Public Functions

| QTemporaryFile()
| QTemporaryFile(QObject *parent)
| QTemporaryFile(const QString &templateName)
| QTemporaryFile(const QString &templateName, QObject *parent)
`(since 6.7)` | QTemporaryFile(const std::filesystem::path &templateName, QObject *parent = nullptr)
virtual | ~QTemporaryFile()
bool | autoRemove() const
QString | fileTemplate() const
bool | open()
bool | rename(const QString &newName)
`(since 6.7)` bool | rename(const std::filesystem::path &newName)
void | setAutoRemove(bool b)
void | setFileTemplate(const QString &templateName)
`(since 6.7)` void | setFileTemplate(const std::filesystem::path &name)

## Reimplemented Public Functions

virtual QString | fileName() const override

## Static Public Members

QTemporaryFile * | createNativeFile(QFile &file)
QTemporaryFile * | createNativeFile(const QString &fileName)
`(since 6.7)` QTemporaryFile * | createNativeFile(const std::filesystem::path &fileName)

## Reimplemented Protected Functions

virtual bool | open(QIODeviceBase::OpenMode mode) override

## Detailed Description

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 will be determined from QCoreApplication::applicationName() (otherwise `qt_temp`) and 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.

It is important to specify the correct directory if the rename() function will be called, as QTemporaryFile can only rename files within the same volume / filesystem as the temporary file itself was created on.

The file name (the part after the last directory path separator in the specified file template) can contain the special sequence `"XXXXXX"` (at least six upper case `"X"` characters), which will be replaced with the auto-generated portion of the file name. If the file name doesn't contain `"XXXXXX"`, QTemporaryFile will append the generated part to the file name. Only the last occurrence of `"XXXXXX"` will be considered.

Note: On Linux, QTemporaryFile will attempt to create unnamed temporary files. If that succeeds, open() will return true but exists() will be false. If you call fileName() or any function that calls it, QTemporaryFile will give the file a name, so most applications will not see a difference.

See also QDir::tempPath() and QFile.

## Member Function Documentation

### QTemporaryFile::QTemporaryFile()

Constructs a QTemporaryFile.

The default file name template is determined from the application name as returned by QCoreApplication::applicationName() (or `"qt_temp"` if the application name is empty), followed by `".XXXXXX"`. The file is stored in the system's temporary directory, as returned by QDir::tempPath().

See also setFileTemplate(), fileTemplate(), fileName(), and QDir::tempPath().

### `[explicit]` QTemporaryFile::QTemporaryFile(QObject *parent)

Constructs a QTemporaryFile with the given parent.

The default file name template is determined from the application name as returned by QCoreApplication::applicationName() (or `"qt_temp"` if the application name is empty), followed by `".XXXXXX"`. The file is stored in the system's temporary directory, as returned by QDir::tempPath().

See also setFileTemplate().

### `[explicit]` QTemporaryFile::QTemporaryFile(const QString &templateName)

Constructs a QTemporaryFile with templateName as the file name template.

Upon opening the temporary file, templateName will be used to create a unique filename.

If the file name (the part after the last directory path separator in templateName) doesn't contain `"XXXXXX"`, it will be added automatically.

`"XXXXXX"` will be replaced with the dynamic part of the file name, which is calculated to be unique.

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.

It is important to specify the correct directory if the rename() function will be called, as QTemporaryFile can only rename files within the same volume / filesystem as the temporary file itself was created on.

See also open() and fileTemplate().

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

Constructs a QTemporaryFile with the specified parent, and templateName as the file name template.

Upon opening the temporary file, templateName will be used to create a unique filename.

If the file name (the part after the last directory path separator in templateName) doesn't contain `"XXXXXX"`, it will be added automatically.

`"XXXXXX"` will be replaced with the dynamic part of the file name, which is calculated to be unique.

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. It is important to specify the correct directory if the rename() function will be called, as QTemporaryFile can only rename files within the same volume / filesystem as the temporary file itself was created on.

See also open() and fileTemplate().

### `[explicit, since 6.7]` QTemporaryFile::QTemporaryFile(const std::filesystem::path &templateName, QObject *parent = nullptr)

This is an overloaded function.

This function was introduced in Qt 6.7.

### `[virtual noexcept]` 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().

### `[static]` QTemporaryFile *QTemporaryFile::createNativeFile(QFile &file)

If file is not already a native file, then a QTemporaryFile is created in QDir::tempPath(), the contents of file is copied into it, and a pointer to the temporary file is returned. Does nothing and returns `0` if file is already a native file.

For example:

       QFile f(":/resources/file.txt");
       QTemporaryFile::createNativeFile(f); // Returns a pointer to a temporary file

       QFile f("/users/qt/file.txt");
       QTemporaryFile::createNativeFile(f); // Returns 0

See also QFileInfo::isNativePath().

### `[static]` QTemporaryFile *QTemporaryFile::createNativeFile(const QString &fileName)

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

This is an overloaded function.

### `[static, since 6.7]` QTemporaryFile *QTemporaryFile::createNativeFile(const std::filesystem::path &fileName)

This is an overloaded function.

This function was introduced in Qt 6.7.

### `[override virtual]` QString QTemporaryFile::fileName() const

Reimplements: QFile::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.

The file name returned by this method is relative or absolute depending on the file name template used to construct this object (or passed to setFileTemplate()) being relative or absolute, respectively.

See also fileTemplate().

### QString QTemporaryFile::fileTemplate() const

Returns the file name template.

The file name template returned by this method, will be relative or absolute depending on the file name template used to construct this object (or passed to setFileTemplate()) being relative or absolute, respectively.

See also setFileTemplate(), fileName(), and Default File Name Template.

### bool QTemporaryFile::open()

Opens a unique temporary file in the file system in QIODeviceBase::ReadWrite mode. Returns `true` if the file was successfully opened, or was already open. Otherwise returns `false`.

If called for the first time, open() will create a unique file name based on fileTemplate(). The file is guaranteed to have been created by this function (that is, it has never existed before).

If a file is reopened after calling close(), the same file will be opened again.

See also setFileTemplate() and QT_USE_NODISCARD_FILE_OPEN.

### `[override virtual protected]` bool QTemporaryFile::open(QIODeviceBase::OpenMode mode)

Reimplements: QFile::open(QIODeviceBase::OpenMode mode).

Opens a unique temporary file in the file system with mode flags. Returns `true` if the file was successfully opened, or was already open. Otherwise returns `false`.

If called for the first time, open() will create a unique file name based on fileTemplate(), and open it with mode flags. The file is guaranteed to have been created by this function (that is, it has never existed before).

If a file is reopened after calling close(), the same file will be opened again with mode flags.

See also setFileTemplate() and QT_USE_NODISCARD_FILE_OPEN.

### bool QTemporaryFile::rename(const QString &newName)

Renames the current temporary file to newName and returns true if it succeeded.

This function has an important difference compared to QFile::rename(): it will not perform a copy+delete if the low-level system call to rename the file fails, something that could happen if newName specifies a file in a different volume or filesystem than the temporary file was created on. In other words, QTemporaryFile only supports atomic file renaming.

This functionality is intended to support materializing the destination file with all contents already present, so another process cannot see an incomplete file in the process of being written. The QSaveFile class can be used for a similar purpose too, particularly if the destination file is not temporary.

Note: Calling rename() does not disable autoRemove. If you want the renamed file to persist, you must call setAutoRemove and set it to `false` after calling rename(). Otherwise, the file will be deleted when the QTemporaryFile object is destroyed.

See also QSaveFile, QSaveFile::commit(), and QFile::rename().

### `[since 6.7]` bool QTemporaryFile::rename(const std::filesystem::path &newName)

This is an overloaded function.

This function was introduced in Qt 6.7.

### void QTemporaryFile::setAutoRemove(bool b)

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

Auto-remove is on by default.

If you set this property to `false`, ensure the application provides a way to remove the file once it is no longer needed, including passing the responsibility on to another process. Always use the fileName() function to obtain the name and never try to guess the name that QTemporaryFile has generated.

On some systems, if fileName() is not called before closing the file, the temporary file may be removed regardless of the state of this property. This behavior should not be relied upon, so application code should either call fileName() or leave the auto removal functionality enabled.

See also autoRemove() and remove().

### void QTemporaryFile::setFileTemplate(const QString &templateName)

Sets the file name template to templateName.

If the file name (the part after the last directory path separator in templateName) doesn't contain `"XXXXXX"`, it will be added automatically.

`"XXXXXX"` will be replaced with the dynamic part of the file name, which is calculated to be unique.

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. It is important to specify the correct directory if the rename() function will be called, as QTemporaryFile can only rename files within the same volume / filesystem as the temporary file itself was created on.

See also fileTemplate() and fileName().

### `[since 6.7]` void QTemporaryFile::setFileTemplate(const std::filesystem::path &name)

This is an overloaded function.

This function was introduced in Qt 6.7.