QFile 类

QFile 类提供用于读写文件的接口。 更多...

Header: #include <QFile>
CMake: find_package(Qt6 COMPONENTS Core REQUIRED)
target_link_libraries(mytarget PRIVATE Qt6::Core)
qmake: QT += core
继承: QFileDevice
继承者:

QTemporaryFile

注意: 此类的所有函数 可重入 .

公共函数

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

重实现公共函数

virtual QString fileName () const override
virtual bool open (QIODeviceBase::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

静态公共成员

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 )
QFileDevice::Permissions permissions (const std::filesystem::path & 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 )
bool setPermissions (const std::filesystem::path & filename , QFileDevice::Permissions permissionSpec )
QString symLinkTarget (const QString & fileName )

详细描述

QFile 是 I/O 设备用于读写文本和二进制文件及 resources 。QFile 可以单独使用,或更方便采用 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 (),和 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 () 返回 true .

直接读取文件

The following example reads a text file line by line:

    QFile file("in.txt");
    if (!file.open(QIODevice::ReadOnly | QIODevice::Text))
        return;
    while (!file.atEnd()) {
        QByteArray line = file.readLine();
        process_line(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.

使用流读取文件

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

    QFile file("in.txt");
    if (!file.open(QIODevice::ReadOnly | QIODevice::Text))
        return;
    QTextStream in(&file);
    while (!in.atEnd()) {
        QString line = in.readLine();
        process_line(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 file is encoded in UTF-8. This can be changed using QTextStream::setEncoding ().

To write text, we can use operator<<(), which is overloaded to take a QTextStream on the left and various data types (including QString ) on the right:

    QFile file("out.txt");
    if (!file.open(QIODevice::WriteOnly | QIODevice::Text))
        return;
    QTextStream out(&file);
    out << "The magic number is: " << 49 << "\n";
							

QDataStream is similar, in that you can use operator<<() to write data and operator>>() to read it back. See the class documentation for details.

When you use QFile, QFileInfo ,和 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 ( <cstdio> or <iostream> ) or platform-specific APIs to access files instead of QFile, you can use the encodeName () 和 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 () 或 readLine () repeatedly until no more data can be read. The next example uses QTextStream to read /proc/modules line by line:

    QFile file("/proc/modules");
    if (!file.open(QIODevice::ReadOnly | QIODevice::Text))
        return;
    QTextStream in(&file);
    QString line = in.readLine();
    while (!line.isNull()) {
        process_line(line);
        line = in.readLine();
    }
							

信号

不像其它 QIODevice 实现,譬如 QTcpSocket ,QFile 不会发射 aboutToClose (), bytesWritten (),或 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.

平台具体问题

文件权限的处理是不同的,在像 Unix 系统和 Windows。在非 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 对文件权限的理解是有限的,这尤其影响 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.

另请参阅 QTextStream , QDataStream , QFileInfo , QDir ,和 Qt 资源系统 .

成员函数文档编制

[since 6.0] QFile:: QFile (const std::filesystem::path & name , QObject * parent )

构造新文件对象采用给定 parent to represent the file with the specified name .

该函数在 Qt 6.0 引入。

QFile:: QFile (const QString & name , QObject * parent )

构造新文件对象采用给定 parent to represent the file with the specified name .

QFile:: QFile ( QObject * parent )

构造新文件对象采用给定 parent .

[since 6.0] QFile:: QFile (const std::filesystem::path & name )

构造新文件对象以表示文件采用给定 name .

该函数在 Qt 6.0 引入。

QFile:: QFile (const QString & name )

构造新文件对象以表示文件采用给定 name .

QFile:: QFile ()

构造 QFile 对象。

[virtual] QFile:: ~QFile ()

销毁文件对象,关闭它若有必要。

bool QFile:: copy (const QString & newName )

拷贝目前指定的文件通过 fileName () 到文件称为 newName 。返回 true 若成功;否则返回 false .

注意:若文件采用名称 newName 已存在,copy() 返回 false (i.e. QFile 不会覆写它)。

关闭源文件在拷贝它之前。

另请参阅 setFileName ().

[since 6.0] bool QFile:: copy (const std::filesystem::path & newName )

这是重载函数。

该函数在 Qt 6.0 引入。

[static] bool QFile:: copy (const QString & fileName , const QString & newName )

这是重载函数。

拷贝文件 fileName to newName 。返回 true 若成功;否则返回 false .

若文件采用名称 newName 已存在,copy() 返回 false (即, QFile 不会覆写它)。

另请参阅 rename ().

[static] QString QFile:: decodeName (const QByteArray & localFileName )

这做反向 QFile::encodeName () 使用 localFileName .

另请参阅 encodeName ().

[static] QString QFile:: decodeName (const char * localFileName )

这是重载函数。

返回 Unicode 版本为给定 localFileName 。见 encodeName () 了解细节。

[static] QByteArray QFile:: encodeName (const QString & fileName )

转换 fileName to the local 8-bit encoding determined by the user's locale. This is sufficient for file names that the user chooses. File names hard-coded into the application should only use 7-bit ASCII filename characters.

另请参阅 decodeName ().

[static] bool QFile:: exists (const QString & fileName )

返回 true 若文件指定通过 fileName 存在;否则返回 false .

注意: fileName 是指向不存在文件的符号链接,返回 false。

bool QFile:: exists () const

这是重载函数。

返回 true 若文件指定通过 fileName () 存在;否则返回 false .

另请参阅 fileName () 和 setFileName ().

[override virtual] QString QFile:: fileName () const

重实现: QFileDevice::fileName () const.

返回名称设置通过 setFileName () or to the QFile 构造函数。

另请参阅 setFileName () 和 QFileInfo::fileName ().

[since 6.0] std::filesystem::path QFile:: filesystemFileName () const

返回 fileName () 作为 std::filesystem::path .

该函数在 Qt 6.0 引入。

Creates a link named linkName that points to the file currently specified by fileName (). What a link is depends on the underlying filesystem (be it a shortcut on Windows or a symbolic link on Unix). Returns true 若成功;否则返回 false .

This function will not overwrite an already existing entity in the file system; in this case, link() will return false and set error() to return RenameError .

注意: To create a valid link on Windows, linkName must have a .lnk file extension.

另请参阅 setFileName ().

这是重载函数。

该函数在 Qt 6.0 引入。

这是重载函数。

Creates a link named linkName that points to the file fileName . What a link is depends on the underlying filesystem (be it a shortcut on Windows or a symbolic link on Unix). Returns true 若成功;否则返回 false .

另请参阅 link ().

[since 5.15] bool QFile:: moveToTrash ()

移动指定文件按 fileName () 到垃圾桶。返回 true 若成功,并设置 fileName () to the path at which the file can be found within the trash; otherwise returns false .

注意: On systems where the system API doesn't report the location of the file in the trash, fileName () will be set to the null string once the file has been moved. On systems that don't have a trash can, this function always returns false.

该函数在 Qt 5.15 引入。

[static, since 5.15] bool QFile:: moveToTrash (const QString & fileName , QString * pathInTrash = nullptr)

这是重载函数。

移动指定文件按 fileName () 到垃圾桶。返回 true if successful, and sets pathInTrash (if provided) to the path at which the file can be found within the trash; otherwise returns false .

注意: On systems where the system API doesn't report the path of the file in the trash, pathInTrash will be set to the null string once the file has been moved. On systems that don't have a trash can, this function always returns false.

该函数在 Qt 5.15 引入。

[override virtual] bool QFile:: open ( QIODeviceBase::OpenMode mode )

重实现: QIODevice::open (QIODeviceBase::OpenMode mode).

Opens the file using OpenMode mode ,返回 true,若成功;否则返回 false。

mode must be QIODevice::ReadOnly, QIODevice::WriteOnly, or QIODevice::ReadWrite. It may also have additional flags, such as QIODevice::Text and QIODevice::Unbuffered.

注意: WriteOnly or ReadWrite mode, if the relevant file does not already exist, this function will try to create a new file before opening it.

另请参阅 QIODevice::OpenMode and setFileName ().

bool QFile:: open ( FILE * fh , QIODeviceBase::OpenMode mode , QFileDevice::FileHandleFlags handleFlags = DontCloseHandle)

这是重载函数。

Opens the existing file handle fh 以给定 mode . handleFlags may be used to specify additional options. Returns true 若成功;否则返回 false .

范例:

#include <stdio.h>
void printError(const char* msg)
{
    QFile file;
    file.open(stderr, QIODevice::WriteOnly);
    file.write(msg, qstrlen(msg));        // write to stderr
    file.close();
}
							

QFile is opened using this function, behaviour of close () is controlled by the AutoCloseHandle flag. If AutoCloseHandle is specified, and this function succeeds, then calling close () closes the adopted handle. Otherwise, close () does not actually close the file, but only flushes it.

警告:

  1. fh does not refer to a regular file, e.g., it is stdin , stdout ,或 stderr , you may not be able to seek (). size () 返回 0 in those cases. See QIODevice::isSequential () 了解更多信息。
  2. Since this function opens the file without specifying the file name, you cannot use this QFile 采用 QFileInfo .

Note for the Windows Platform

fh must be opened in binary mode (i.e., the mode string must contain 'b', as in "rb" or "wb") when accessing files and other random-access devices. Qt will translate the end-of-line characters if you pass QIODevice::Text to mode . Sequential devices, such as stdin and stdout, are unaffected by this limitation.

You need to enable support for console applications in order to use the stdin, stdout and stderr streams at the console. To do this, add the following declaration to your application's project file:

CONFIG += console
							

另请参阅 close ().

bool QFile:: open ( int fd , QIODeviceBase::OpenMode mode , QFileDevice::FileHandleFlags handleFlags = DontCloseHandle)

这是重载函数。

Opens the existing file descriptor fd 以给定 mode . handleFlags may be used to specify additional options. Returns true 若成功;否则返回 false .

QFile is opened using this function, behaviour of close () is controlled by the AutoCloseHandle flag. If AutoCloseHandle is specified, and this function succeeds, then calling close () closes the adopted handle. Otherwise, close () does not actually close the file, but only flushes it.

警告: fd is not a regular file, e.g, it is 0 ( stdin ), 1 ( stdout ), or 2 ( stderr ), you may not be able to seek (). In those cases, size () 返回 0 。见 QIODevice::isSequential () 了解更多信息。

警告: Since this function opens the file without specifying the file name, you cannot use this QFile 采用 QFileInfo .

另请参阅 close ().

[override virtual] QFileDevice::Permissions QFile:: permissions () const

重实现: QFileDevice::permissions () const.

另请参阅 setPermissions ().

[static] QFileDevice::Permissions QFile:: permissions (const QString & fileName )

这是重载函数。

Returns the complete OR-ed together combination of QFile::Permission for fileName .

[static, since 6.0] QFileDevice::Permissions QFile:: permissions (const std::filesystem::path & filename )

这是重载函数。

该函数在 Qt 6.0 引入。

bool QFile:: remove ()

Removes the file specified by fileName ()。返回 true 若成功;否则返回 false .

The file is closed before it is removed.

另请参阅 setFileName ().

[static] bool QFile:: remove (const QString & fileName )

这是重载函数。

Removes the file specified by the fileName 给定。

返回 true 若成功;否则返回 false .

另请参阅 remove ().

bool QFile:: rename (const QString & newName )

Renames the file currently specified by fileName () 到 newName 。返回 true 若成功;否则返回 false .

若文件采用名称 newName already exists, rename() returns false (即, QFile 不会覆写它)。

The file is closed before it is renamed.

If the rename operation fails, Qt will attempt to copy this file's contents to newName , and then remove this file, keeping only newName . If that copy operation fails or this file can't be removed, the destination file newName is removed to restore the old state.

另请参阅 setFileName ().

[since 6.0] bool QFile:: rename (const std::filesystem::path & newName )

这是重载函数。

该函数在 Qt 6.0 引入。

[static] bool QFile:: rename (const QString & oldName , const QString & newName )

这是重载函数。

Renames the file oldName to newName 。返回 true 若成功;否则返回 false .

若文件采用名称 newName already exists, rename() returns false (即, QFile 不会覆写它)。

另请参阅 rename ().

[override virtual] bool QFile:: resize ( qint64 sz )

重实现: QFileDevice::resize (qint64 sz).

[static] bool QFile:: resize (const QString & fileName , qint64 sz )

这是重载函数。

设置 fileName to size (in bytes) sz 。返回 true if the resize succeeds; false otherwise. If sz is larger than fileName currently is the new bytes will be set to 0, if sz is smaller the file is simply truncated.

警告: This function can fail if the file doesn't exist.

另请参阅 resize ().

void QFile:: setFileName (const QString & name )

设置 name of the file. The name can have no path, a relative path, or an absolute path.

Do not call this function if the file has already been opened.

If the file name has no path or a relative path, the path used will be the application's current directory path at the time of the open () 调用。

范例:

QFile file;
QDir::setCurrent("/tmp");
file.setFileName("readme.txt");
QDir::setCurrent("/home");
file.open(QIODevice::ReadOnly);      // opens "/home/readme.txt" under Unix
							

Note that the directory separator "/" works for all operating systems supported by Qt.

另请参阅 fileName (), QFileInfo ,和 QDir .

[since 6.0] void QFile:: setFileName (const std::filesystem::path & name )

这是重载函数。

该函数在 Qt 6.0 引入。

[override virtual] bool QFile:: setPermissions ( QFileDevice::Permissions permissions )

重实现: QFileDevice::setPermissions (QFileDevice::Permissions permissions).

Sets the permissions for the file to the permissions 指定。返回 true 若成功,或 false 若权限不能被修改。

警告: 此函数不操纵 ACL (访问控制列表),这可能限制其有效性。

另请参阅 permissions () 和 setFileName ().

[static] bool QFile:: setPermissions (const QString & fileName , QFileDevice::Permissions permissions )

这是重载函数。

设置权限为 fileName file to permissions .

[static, since 6.0] bool QFile:: setPermissions (const std::filesystem::path & filename , QFileDevice::Permissions permissionSpec )

这是重载函数。

该函数在 Qt 6.0 引入。

[override virtual] qint64 QFile:: size () const

重实现: QFileDevice::size () const.

[static] QString QFile:: symLinkTarget (const QString & fileName )

Returns the absolute path of the file or directory referred to by the symlink (or shortcut on Windows) specified by fileName , or returns an empty string if the fileName does not correspond to a symbolic link.

This name may not represent an existing file; it is only a string. QFile::exists () 返回 true if the symlink points to an existing file.

QString QFile:: symLinkTarget () const

这是重载函数。

Returns the absolute path of the file or directory a symlink (or shortcut on Windows) points to, or a an empty string if the object isn't a symbolic link.

This name may not represent an existing file; it is only a string. QFile::exists () 返回 true if the symlink points to an existing file.

另请参阅 fileName () 和 setFileName ().