QTextStream & QString 配合

把QString视为一Stream使用。

QTextStream的相关函数

QTextStream ( QString * string, QIODevice::OpenMode openMode = QIODevice::ReadWrite )

void setString ( QString * string, QIODevice::OpenMode openMode = QIODevice::ReadWrite )

bool QTextStream::atEnd () const

Returns true if there is no more data to be read from the QTextStream; otherwise returns false. This is similar to, but not the same as calling QIODevice::atEnd(), as QTextStream also takes into account its internal Unicode buffer.

qint64 QTextStream::pos () const

Returns the device position corresponding to the current position of the stream, or -1 if an error occurs (e.g., if there is no device or string, or if there's a device error).

Because QTextStream is buffered, this function may have to seek the device to reconstruct a valid device position. This operation can be expensive, so you may want to avoid calling this function in a tight loop.

bool QTextStream::seek ( qint64 pos )

Seeks to the position pos in the device. Returns true on success; otherwise returns false.

Status QTextStream::status () const

Returns the status of the text stream.

QTextStream::Ok
0
The text stream is operating normally.

QTextStream::ReadPastEnd
1
The text stream has read past the end of the data in the underlying device.

QTextStream::ReadCorruptData
2
The text stream has read corrupt data.

 

QString的相关函数

 

bool QString::isEmpty () const

Returns true if the string has no characters; otherwise returns false.

Example:

     QString().isEmpty();            // returns true
     QString("").isEmpty();          // returns true
     QString("x").isEmpty();         // returns false
     QString("abc").isEmpty();       // returns false

bool QString::isNull () const

Returns true if this string is null; otherwise returns false.

Example:

     QString().isNull();             // returns true
     QString("").isNull();           // returns false
     QString("abc").isNull();        // returns false

Qt makes a distinction between null strings and empty strings for historical reasons. For most applications, what matters is whether or not a string contains any data, and this can be determined using the isEmpty() function.