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// Copyright (C) 2016 The Qt Company Ltd.
// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR GFDL-1.3-no-invariants-only
/*!
\page io-functions.html
\title File and Datastream Functions
The QIODevice class is the base interface class of all I/O devices in
\l{Qt Core}. QIODevice provides both a common implementation and an
abstract interface for devices that support reading and writing of blocks
of data. The device can be a memory buffer, a file, or a datastream.
Some subclasses like QFile have been implemented using a memory buffer for
intermediate storing of data. This speeds up programs by reducing
read/write operations. Buffering makes functions like \l{QFile::}{getChar()} and
\l{QFile::}{putChar()} fast, as they can operate on the memory buffer instead of
directly on the device itself.
The QFile class provides functions for reading from and writing to files.
A QFile may be used by itself or, more conveniently, with a QTextStream or
QDataStream.
QBuffer allows you to access a QByteArray using the QIODevice interface.
The QByteArray is treated just as a standard random-accessed file.
An example:
\code
QBuffer buffer;
char ch;
buffer.open(QBuffer::ReadWrite);
buffer.write("Qt rocks!");
buffer.seek(0);
buffer.getChar(&ch); // ch == 'Q'
buffer.getChar(&ch); // ch == 't'
buffer.getChar(&ch); // ch == ' '
buffer.getChar(&ch); // ch == 'r'
\endcode
Call \l{QBuffer::}{open()} to open the buffer. Then call \l{QBuffer::}{write()} or \l{QBuffer::}{putChar()} to write to
the buffer, and \l{QBuffer::}{read()}, \l{QBuffer::}{readLine()}, \l{QBuffer::}{readAll()}, or \l{QBuffer::}{getChar()} to read from it.
\l{QBuffer::}{size()} returns the current size of the buffer, and you can seek to arbitrary
positions in the buffer by calling \l{QBuffer::}{seek()}. When you are done with accessing
the buffer, call \l{QBuffer::}{close()}.
The QDataStream class provides serialization of binary data to a QIODevice.
A data stream is a binary stream of encoded information which is 100% inde-
pendent of the host computer's operating system, CPU or byte order. For
example, a data stream that is written by a PC under Windows can be read
by a Sun SPARC running Solaris. You can also use a data stream to read/write
raw unencoded binary data.
For more details on the datatypes that QDataStream can serialize, see
\l{Serializing Qt Data Types}.
The QTextStream class provides a convenient interface for reading and
writing text. QTextStream can operate on a QIODevice, a QByteArray or
a QString. Using QTextStream's streaming operators, you can conveniently read
and write words, lines and numbers. It's also common to use QTextStream to
read console input and write console output.
There are three general ways to use QTextStream when reading text files:
\list
\li Chunk by chunk, by calling \l{QBuffer::readLine()}{readLine()} or \l{QBuffer::readAll()}{readAll()}.
\li Word by word. QTextStream supports streaming into \l{QString}s, \l{QByteArray}s
and char* buffers. Words are delimited by space, and leading white space
is automatically skipped.
\li Character by character, by streaming into QChar or char types. This
method is often used for convenient input handling when parsing files,
independent of character encoding and end-of-line semantics. To skip
white space, call \l{QTextStream::}{skipWhiteSpace()}.
\endlist
QByteArray can be used to store both raw bytes (including \c{\0}) and traditional
8-bit '\\0'-terminated strings. Using QByteArray is much more convenient
than using const char *. It always ensures that the data is followed by a '\\0'
terminator, and uses \l{Implicit Sharing}{implicitly shared classes} (copy-on-write)
to reduce memory usage and avoid needless copying of data.
In addition to QByteArray, Qt also provides the QString class to store string
data. For most purposes, QString is the most appropriate class to use. It stores
16-bit Unicode characters. It is, however, a good idea to use QByteArray when you
need to store raw binary data, and when memory conservation is critical (for
example, with Qt for Embedded Linux).
*/
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