QTextStream Class Reference

The QTextStream class provides basic functions for reading and writing text using a QIODevice. More...

#include <qtextstream.h>

Inherited by QTextIStream and QTextOStream.

List of all member functions.

Public Members

• enum Encoding { Locale, Latin1, Unicode, UnicodeNetworkOrder, UnicodeReverse, RawUnicode, UnicodeUTF8 }
• void setEncoding ( Encoding ) 
• void setCodec ( QTextCodec * ) 
• QTextStream () 
• QTextStream ( QIODevice * ) 
• QTextStream ( QString *, int mode ) 
• QTextStream ( QString &, int mode ) (obsolete)
• QTextStream ( QByteArray, int mode ) 
• QTextStream ( FILE *, int mode ) 
• virtual ~QTextStream () 
• QIODevice* device () const
• void setDevice ( QIODevice * ) 
• void unsetDevice () 
• bool atEnd () const
• bool eof () const (obsolete)
• QTextStream& operator>> ( QChar & ) 
• QTextStream& operator>> ( char & ) 
• QTextStream& operator>> ( signed short & ) 
• QTextStream& operator>> ( unsigned short & ) 
• QTextStream& operator>> ( signed int & ) 
• QTextStream& operator>> ( unsigned int & ) 
• QTextStream& operator>> ( signed long & ) 
• QTextStream& operator>> ( unsigned long & ) 
• QTextStream& operator>> ( float & ) 
• QTextStream& operator>> ( double & ) 
• QTextStream& operator>> ( char * ) 
• QTextStream& operator>> ( QString & ) 
• QTextStream& operator>> ( QCString & ) 
• QTextStream& operator<< ( QChar ) 
• QTextStream& operator<< ( char ) 
• QTextStream& operator<< ( signed short ) 
• QTextStream& operator<< ( unsigned short ) 
• QTextStream& operator<< ( signed int ) 
• QTextStream& operator<< ( unsigned int ) 
• QTextStream& operator<< ( signed long ) 
• QTextStream& operator<< ( unsigned long ) 
• QTextStream& operator<< ( float ) 
• QTextStream& operator<< ( double ) 
• QTextStream& operator<< ( const char * ) 
• QTextStream& operator<< ( const QString & ) 
• QTextStream& operator<< ( const QCString & ) 
• QTextStream& operator<< ( void * ) 
• QTextStream& readRawBytes ( char *, uint len ) 
• QTextStream& writeRawBytes ( const char *, uint len ) 
• QString readLine () 
• QString read () 
• void skipWhiteSpace () 
• enum { skipws = 0x0001, left = 0x0002, right = 0x0004, internal = 0x0008, bin = 0x0010, oct = 0x0020, dec = 0x0040, hex = 0x0080, showbase = 0x0100, showpoint = 0x0200, uppercase = 0x0400, showpos = 0x0800, scientific= 0x1000, fixed = 0x2000 }
• int flags () const
• int flags ( int f ) 
• int setf ( int bits ) 
• int setf ( int bits, int mask ) 
• int unsetf ( int bits ) 
• void reset () 
• int width () const
• int width ( int ) 
• int fill () const
• int fill ( int ) 
• int precision () const
• int precision ( int ) 

Detailed Description

The text stream class has a functional interface that is very similar to that of the standard C++ iostream class. The difference between iostream and QTextStream is that our stream operates on a QIODevice, which is easily subclassed, while iostream operates on FILE * pointers, which can not be subclassed.

Qt provides several global functions similar to the ones in iostream:

• bin sets the QTextStream to read/write binary numbers
• oct sets the QTextStream to read/write octal numbers
• dec sets the QTextStream to read/write decimal numbers
• hex sets the QTextStream to read/write hexadecimal numbers
• endl forces a line break
• flush forces the QIODevice to flush any buffered data
• ws eats any available white space (on input)
• reset resets the QTextStream to its default mode (see reset()).

Warning: By default, QTextStream will automatically detect whether integers in the stream are in decimal, octal, hexadecimal or binary format when reading from the stream. In particular, a leading '0' signifies octal, ie. the sequence "0100" will be interpreted as 64.

The QTextStream class reads and writes text and it is not appropriate for dealing with binary data (but QDataStream is).

By default output of Unicode text (ie. QString) is done using the local 8-bit encoding. This can be changed using the setEncoding() method. For input, the QTextStream will auto-detect standard Unicode "byte order marked" text files, but otherwise the local 8-bit encoding is used.

See also QDataStream.

Examples: grapher/grapher.cpp

Member Function Documentation

QTextStream::QTextStream ()

Constructs a data stream that has no IO device.

QTextStream::QTextStream ( QByteArray a, int mode )

Constructs a text stream that operates on a byte array through an internal QBuffer device.

Example:

    QByteArray array;
    QTextStream ts( array, IO_WriteOnly );
    ts << "pi = " << 3.14 << '\0';              // array == "pi = 3.14"

Writing data to the text stream will modify the contents of the array. The array will be expanded when data is written beyond the end of the string.

Same example, using a QBuffer:

    QByteArray array;
    QBuffer buf( array );
    buf.open( IO_WriteOnly );
    QTextStream ts( &buf );
    ts << "pi = " << 3.14 << '\0';              // array == "pi = 3.14"
    buf.close();

QTextStream::QTextStream ( QIODevice * iod )

Constructs a text stream that uses the IO device iod.

QTextStream::QTextStream ( QString & str, int filemode )

This function is obsolete. It is provided to keep old source working, and will probably be removed in a future version of Qt. We strongly advise against using it in new code.

This constructor is equivalent to the constructor taking a QString* parameter.

QTextStream::QTextStream ( QString * str, int filemode )

Constructs a text stream that operates on a Unicode QString through an internal device.

If you set an encoding or codec with setEncoding() or setCodec(), this setting is ignored for text streams that operate on QString.

Example:

    QString str;
    QTextStream ts( &str, IO_WriteOnly );
    ts << "pi = " << 3.14;                      // str == "pi = 3.14"

Writing data to the text stream will modify the contents of the string. The string will be expanded when data is written beyond the end of the string. Note that the string will not be truncated:

    QString str = "pi = 3.14";
    QTextStream ts( &str, IO_WriteOnly );
    ts <<  "2+2 = " << 2+2;             // str == "2+2 = 414"

Note that since QString is Unicode, you should not use readRawBytes() or writeRawBytes() on such a stream.

QTextStream::QTextStream ( FILE * fh, int mode )

Constructs a text stream that operates on an existing file handle fh through an internal QFile device.

Example:

    QTextStream cout( stdout, IO_WriteOnly );
    QTextStream cin ( stdin,  IO_ReadOnly );
    QTextStream cerr( stderr, IO_WriteOnly );

QTextStream::~QTextStream () [virtual]

Destructs the text stream.

The destructor does not affect the current IO device.

bool QTextStream::atEnd () const

Returns TRUE if the IO device has reached the end position (end of stream or file) or if there is no IO device set.

Returns FALSE if the current position of the read/write head of the IO device is somewhere before the end position.

See also QIODevice::atEnd().

QIODevice * QTextStream::device () const

Returns the IO device currently set.

See also setDevice() and unsetDevice().

bool QTextStream::eof () const

This function is obsolete. It is provided to keep old source working, and will probably be removed in a future version of Qt. We strongly advise against using it in new code.

This function has been renamed to atEnd().

See also QIODevice::atEnd().

Examples: grapher/grapher.cpp

int QTextStream::fill () const

Returns the fill character. The default value is ' ' (space).

int QTextStream::fill ( int f )

Sets the fill character to f. Returns the previous fill character.

int QTextStream::flags () const

Returns the current stream flags. The default value is 0.

The meaning of the flags are:

• skipws - Not currently used - whitespace always skipped
• left - Numeric fields are left-aligned
• right - Not currently used (by default numerics are right aligned)
• internal - Put any padding spaces between +/- and value
• bin - Output and input only in binary
• oct - Output and input only in octal
• dec - Output and input only in decimal
• hex - Output and input only in hexadecimal
• showbase - Annotate numeric outputs with 0b, 0, or 0x if in bin, oct, or hex format
• showpoint - Not currently used
• uppercase - Use 0B and 0X rather than 0b and 0x
• showpos - Show + for positive numeric values
• scientific - Use scientific notation for floating point values
• fixed - Use fixed-point notation for floating point values

Note that unless bin, oct, dec, or hex is set, the input base is octal if the value starts with 0, hexadecimal if it starts with 0x, binary if the value starts with 0b, and decimal otherwise.

See also setf() and unsetf().

int QTextStream::flags ( int f )

Sets the stream flags to f. Returns the previous stream flags.

See also setf(), unsetf() and flags().

QTextStream & QTextStream::operator<< ( QChar c )

Writes a char to the stream and returns a reference to the stream.

The character c is assumed to be Latin1 encoded independent of the Encoding set for the QTextStream.

QTextStream & QTextStream::operator<< ( char c )

Writes a char to the stream and returns a reference to the stream.

QTextStream & QTextStream::operator<< ( const QCString & s )

Writes s to the stream and returns a reference to the stream.

The string s is assumed to be Latin1 encoded independent of the Encoding set for the QTextStream.

QTextStream & QTextStream::operator<< ( const QString & s )

Writes s to the stream and returns a reference to the stream.

QTextStream & QTextStream::operator<< ( const char * s )

Writes a string to the stream and returns a reference to the stream.

The string s is assumed to be Latin1 encoded independent of the Encoding set for the QTextStream.

QTextStream & QTextStream::operator<< ( double f )

Writes a double to the stream and returns a reference to the stream.

QTextStream & QTextStream::operator<< ( float f )

Writes a float to the stream and returns a reference to the stream.

QTextStream & QTextStream::operator<< ( signed int i )

Writes an int to the stream and returns a reference to the stream.

QTextStream & QTextStream::operator<< ( signed long i )

Writes a long int to the stream and returns a reference to the stream.

QTextStream & QTextStream::operator<< ( signed short i )

Writes a short integer to the stream and returns a reference to the stream.

QTextStream & QTextStream::operator<< ( unsigned int i )

Writes an unsigned int to the stream and returns a reference to the stream.

QTextStream & QTextStream::operator<< ( unsigned long i )

Writes an unsigned long int to the stream and returns a reference to the stream.

QTextStream & QTextStream::operator<< ( unsigned short i )

Writes an unsigned short integer to the stream and returns a reference to the stream.

QTextStream & QTextStream::operator<< ( void * ptr )

Writes a pointer to the stream and returns a reference to the stream.

The ptr is output as an unsigned long hexadecimal integer.

QTextStream & QTextStream::operator>> ( QChar & c )

Reads a char from the stream and returns a reference to the stream. Note that whitespace is not skipped.

QTextStream & QTextStream::operator>> ( QCString & str )

Reads a word from the stream and returns a reference to the stream.

QTextStream & QTextStream::operator>> ( QString & str )

Reads a word from the stream and returns a reference to the stream.

QTextStream & QTextStream::operator>> ( char & c )

Reads a char from the stream and returns a reference to the stream. Note that whitespace is skipped.

QTextStream & QTextStream::operator>> ( char * s )

Reads a word from the stream and returns a reference to the stream.

QTextStream & QTextStream::operator>> ( double & f )

Reads a double from the stream and returns a reference to the stream. See flags() for an explanation of expected input format.

QTextStream & QTextStream::operator>> ( float & f )

Reads a float from the stream and returns a reference to the stream. See flags() for an explanation of expected input format.

QTextStream & QTextStream::operator>> ( signed int & i )

Reads a signed int from the stream and returns a reference to the stream. See flags() for an explanation of expected input format.

QTextStream & QTextStream::operator>> ( signed long & i )

Reads a signed long int from the stream and returns a reference to the stream. See flags() for an explanation of expected input format.

QTextStream & QTextStream::operator>> ( signed short & i )

Reads a signed short integer from the stream and returns a reference to the stream. See flags() for an explanation of expected input format.

QTextStream & QTextStream::operator>> ( unsigned int & i )

Reads an unsigned int from the stream and returns a reference to the stream. See flags() for an explanation of expected input format.

QTextStream & QTextStream::operator>> ( unsigned long & i )

Reads an unsigned long int from the stream and returns a reference to the stream. See flags() for an explanation of expected input format.

QTextStream & QTextStream::operator>> ( unsigned short & i )

Reads an unsigned short integer from the stream and returns a reference to the stream. See flags() for an explanation of expected input format.

int QTextStream::precision () const

Returns the precision. The default value is 6.

int QTextStream::precision ( int p )

Sets the precision to p. Returns the previous precision setting.

QString QTextStream::read ()

Reads the entire stream and returns a string containing the text.

See also QIODevice::readLine().

QString QTextStream::readLine ()

Reads a line from the stream and returns a string containing the text.

The returned string does not contain any trailing newline or carriage return. Note that this is different from QIODevice::readLine(), which does not strip the newline at the end of the line.

On EOF you will get a QString that is null. On reading an empty line the returned QString is empty but not null.

See also QIODevice::readLine().

QTextStream & QTextStream::readRawBytes ( char * s, uint len )

Reads len bytes from the stream into e s and returns a reference to the stream.

The buffer s must be preallocated.

Note that no encoding is done by this function.

Warning: The behaviour of this function is undefined unless the stream's encoding is set to Unicode or Latin1.

See also QIODevice::readBlock().

void QTextStream::reset ()

Resets the text stream.

• All flags are set to 0.
• The field width is set to 0.
• The fill character is set to ' ' (space).
• The precision is set to 6.

See also setf(), width(), fill() and precision().

void QTextStream::setCodec ( QTextCodec * codec )

Sets the codec for this stream to codec. Will not try to autodetect Unicode.

Note that this function should be called before any data is read to/written from the stream.

See also setEncoding().

void QTextStream::setDevice ( QIODevice * iod )

Sets the IO device to iod.

See also device() and unsetDevice().

void QTextStream::setEncoding ( Encoding e )

Sets the encoding of this stream to e, where e is one of:

• Locale Using local file format (Latin1 if locale is not set), but autodetecting Unicode(utf16) on input.
• Unicode Using Unicode(utf16) for input and output. Output will be written in the order most efficient for the current platform (i.e. the order used internally in QString).
• UnicodeUTF8 Using Unicode(utf8) for input and output. If you use it for input it will autodetect utf16 and use it instead of utf8.
• Latin1 ISO-8859-1. Will not autodetect utf16.
• UnicodeNetworkOrder Using network order Unicode(utf16) for input and output. Useful when reading Unicode data that does not start with the byte order marker.
• UnicodeReverse Using reverse network order Unicode(utf16) for input and output. Useful when reading Unicode data that does not start with the byte order marker, or writing data that should be read by buggy Windows applications.
• RawUnicode Like Unicode, but does not write the byte order marker, nor does it autodetect the byte order. Only useful when writing to non-persistent storage used by a single process.

Locale and all Unicode encodings, except RawUnicode, will look at the first two bytes in a input stream to determine the byte order. The initial byte order marker will be stripped off before data is read.

Note that this function should be called before any data is read to/written from the stream.

See also setCodec().

int QTextStream::setf ( int bits )

Sets the stream flag bits bits. Returns the previous stream flags.

Equivalent to flags( flags() | bits ).

See also setf() and unsetf().

int QTextStream::setf ( int bits, int mask )

Sets the stream flag bits bits with a bit mask mask. Returns the previous stream flags.

Equivalent to flags( (flags() & ~mask) | (bits & mask) ).

See also setf() and unsetf().

void QTextStream::skipWhiteSpace ()

Positions the read pointer at the first non-whitespace character.

void QTextStream::unsetDevice ()

Unsets the IO device. Equivalent to setDevice( 0 ).

See also device() and setDevice().

int QTextStream::unsetf ( int bits )

Clears the stream flag bits bits. Returns the previous stream flags.

Equivalent to flags( flags() & ~mask ).

See also setf().

int QTextStream::width () const

Returns the field width. The default value is 0.

int QTextStream::width ( int w )

Sets the field width to w. Returns the previous field width.

QTextStream & QTextStream::writeRawBytes ( const char * s, uint len )

Writes the len bytes from s to the stream and returns a reference to the stream.

Note that no encoding is done by this function.

See also QIODevice::writeBlock().

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