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QTextStream Class Reference

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

All the functions in this class are reentrant when Qt is built with thread support.

#include <qtextstream.h>

Inherited by QTextIStream and QTextOStream.

List of all member functions.

Public Members

Detailed Description

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

The text stream class has a functional interface that is very similar to that of the standard C++ iostream class.

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

Function Meaning
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 whitespace (on input)
reset resets the QTextStream to its default mode (see reset())
qSetW(int) sets the field width to the given argument
qSetFill(int) sets the fill character to the given argument
qSetPrecision(int) sets the precision to the given argument

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, i.e. the sequence "0100" will be interpreted as 64.

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

By default, output of Unicode text (i.e. 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; otherwise the local 8-bit encoding is used.

The QIODevice is set in the constructor, or later using setDevice(). If the end of the input is reached atEnd() returns TRUE. Data can be read into variables of the appropriate type using the operator>>() overloads, or read in its entirety into a single string using read(), or read a line at a time using readLine(). Whitespace can be skipped over using skipWhiteSpace(). You can set flags for the stream using flags() or setf(). The stream also supports width(), precision() and fill(); use reset() to reset the defaults.

See also QDataStream, Input/Output and Networking, and Text Related Classes.

Member Type Documentation

QTextStream::Encoding

  • QTextStream::Locale
  • QTextStream::Latin1
  • QTextStream::Unicode
  • QTextStream::UnicodeNetworkOrder
  • QTextStream::UnicodeReverse
  • QTextStream::RawUnicode
  • QTextStream::UnicodeUTF8

See setEncoding() for an explanation of the encodings.

Member Function Documentation

QTextStream::QTextStream ()

Constructs a data stream that has no IO device.

QTextStream::QTextStream ( QIODevice * iod )

Constructs a text stream that uses the IO device iod.

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

Constructs a text stream that operates on the Unicode QString, str, through an internal device. The filemode argument is passed to the device's open() function; see QIODevice::mode().

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

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

This function is obsolete. It is provided to keep old source working. We strongly advise against using it in new code.

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

QTextStream::QTextStream ( QByteArray a, int mode )

Constructs a text stream that operates on the byte array, a, through an internal QBuffer device. The mode argument is passed to the device's open() function; see QIODevice::mode().

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 ( FILE * fh, int mode )

Constructs a text stream that operates on an existing file handle fh through an internal QFile device. The mode argument is passed to the device's open() function; see QIODevice::mode().

Note that if you create a QTextStream cout or another name that is also used for another variable of a different type, some linkers may confuse the two variables, which will often cause crashes.

QTextStream::~QTextStream () [virtual]

Destroys 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 the stream or file) or if there is no IO device set; otherwise returns FALSE.

See also QIODevice::atEnd().

Examples: addressbook/centralwidget.cpp and grapher/grapher.cpp.

QTextCodec * QTextStream::codec ()

Returns the codec actually used for this stream.

If Unicode is automatically detected in input, a codec with name() "ISO-10646-UCS-2" is returned.

See also setCodec().

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. We strongly advise against using it in new code.

This function has been renamed to atEnd().

See also QIODevice::atEnd().

Example: chart/chartform_files.cpp.

int QTextStream::fill () const

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

int QTextStream::fill ( int f )

This is an overloaded member function, provided for convenience. It behaves essentially like the above function.

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.

Flag Meaning
skipws Not currently used; whitespace always skipped
left Numeric fields are left-aligned
right Not currently used (by default, numerics are right-aligned)
internal Puts 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 Annotates numeric outputs with 0b, 0, or 0x if in bin, oct, or hex format
showpoint Not currently used
uppercase Uses 0B and 0X rather than 0b and 0x
showpos Shows + for positive numeric values
scientific Uses scientific notation for floating point values
fixed Uses 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 it starts with 0b, and decimal otherwise.

See also setf() and unsetf().

int QTextStream::flags ( int f )

This is an overloaded member function, provided for convenience. It behaves essentially like the above function.

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

See also setf() and unsetf().

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

Writes character 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 )

This is an overloaded member function, provided for convenience. It behaves essentially like the above function.

Writes character c to the stream and returns a reference to the stream.

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

This is an overloaded member function, provided for convenience. It behaves essentially like the above function.

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

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

This is an overloaded member function, provided for convenience. It behaves essentially like the above function.

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

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

This is an overloaded member function, provided for convenience. It behaves essentially like the above function.

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

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

This is an overloaded member function, provided for convenience. It behaves essentially like the above function.

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

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

This is an overloaded member function, provided for convenience. It behaves essentially like the above function.

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

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

This is an overloaded member function, provided for convenience. It behaves essentially like the above function.

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

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

This is an overloaded member function, provided for convenience. It behaves essentially like the above function.

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

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

This is an overloaded member function, provided for convenience. It behaves essentially like the above function.

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

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

This is an overloaded member function, provided for convenience. It behaves essentially like the above function.

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<< ( const QString & s )

This is an overloaded member function, provided for convenience. It behaves essentially like the above function.

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

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

This is an overloaded member function, provided for convenience. It behaves essentially like the above function.

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<< ( void * ptr )

This is an overloaded member function, provided for convenience. It behaves essentially like the above function.

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

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

This is an overloaded member function, provided for convenience. It behaves essentially like the above function.

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

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

This is an overloaded member function, provided for convenience. It behaves essentially like the above function.

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

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

This is an overloaded member function, provided for convenience. It behaves essentially like the above function.

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

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

This is an overloaded member function, provided for convenience. It behaves essentially like the above function.

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

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

This is an overloaded member function, provided for convenience. It behaves essentially like the above function.

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

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

This is an overloaded member function, provided for convenience. It behaves essentially like the above function.

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

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

This is an overloaded member function, provided for convenience. It behaves essentially like the above function.

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

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

This is an overloaded member function, provided for convenience. It behaves essentially like the above function.

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

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

This is an overloaded member function, provided for convenience. It behaves essentially like the above function.

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

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

This is an overloaded member function, provided for convenience. It behaves essentially like the above function.

Reads a "word" from the stream into s and returns a reference to the stream.

A word consists of characters for which isspace() returns FALSE.

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

This is an overloaded member function, provided for convenience. It behaves essentially like the above function.

Reads a "word" from the stream into str and returns a reference to the stream.

A word consists of characters for which isspace() returns FALSE.

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

This is an overloaded member function, provided for convenience. It behaves essentially like the above function.

Reads a "word" from the stream into str and returns a reference to the stream.

A word consists of characters for which isspace() returns FALSE.

int QTextStream::precision () const

Returns the precision. The default value is 6.

int QTextStream::precision ( int p )

This is an overloaded member function, provided for convenience. It behaves essentially like the above function.

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

QString QTextStream::read ()

Reads the entire stream from the current position, and returns a string containing the text.

See also QIODevice::readLine().

Examples: action/application.cpp, application/application.cpp, mdi/application.cpp, qdir/qdir.cpp, and qwerty/qwerty.cpp.

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().

Examples: addressbook/centralwidget.cpp, chart/element.cpp, and network/clientserver/server/server.cpp.

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

Reads len bytes from the stream into 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 behavior 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() and codec().

Example: qwerty/qwerty.cpp.

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 the following values:
Encoding Meaning
Locale Uses local file format (Latin1 if locale is not set), but autodetecting Unicode(utf16) on input.
Unicode Uses 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 Uses network order Unicode(utf16) for input and output. Useful when reading Unicode data that does not start with the byte order marker.
UnicodeReverse Uses reverse network order Unicode(utf16) for input and output. Useful when reading Unicode data that does not start with the byte order marker or when writing data that should be read by buggy Windows applications.
RawUnicode Like Unicode, but does not write the byte order marker nor does it auto-detect the byte order. Useful only 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 an 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 or written from the stream.

See also setCodec().

Examples: addressbook/centralwidget.cpp, network/httpd/httpd.cpp, and qwerty/qwerty.cpp.

int QTextStream::setf ( int bits )

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

Equivalent to flags( flags() | bits ).

See also unsetf().

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

This is an overloaded member function, provided for convenience. It behaves essentially like the above function.

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 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 )

This is an overloaded member function, provided for convenience. It behaves essentially like the above function.

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().

This file is part of the Qt toolkit. Copyright © 1995-2005 Trolltech. All Rights Reserved.
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