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Doc: QDataStream doc example

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Updated the example description

Fixes: QTBUG-123035
Change-Id: I3dc953b02297e6e6bd9aecbc2e8831f13cf48715
Reviewed-by: Ivan Solovev <ivan.solovev@qt.io>
(cherry picked from commit 210063a3cfcbe5fa9506ea14fd27787765ae2e9b)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>
This commit is contained in:
Jaishree Vyas 2024-03-28 10:07:21 +01:00 committed by Qt Cherry-pick Bot
parent 2141c7998a
commit fadeb174bc
1 changed files with 20 additions and 7 deletions
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27
src/corelib/serialization/qdatastream.cpp
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@ -70,17 +70,30 @@ constexpr quint32 QDataStream::ExtendedSize;
need of manually defining streaming operators. Enum classes are need of manually defining streaming operators. Enum classes are
serialized using the declared size. serialized using the declared size.
To take one example, a \c{char *} string is written as a 32-bit
integer equal to the length of the string including the '\\0' byte,
followed by all the characters of the string including the
'\\0' byte. When reading a \c{char *} string, 4 bytes are read to
create the 32-bit length value, then that many characters for the
\c {char *} string including the '\\0' terminator are read.
The initial I/O device is usually set in the constructor, but can be The initial I/O device is usually set in the constructor, but can be
changed with setDevice(). If you've reached the end of the data changed with setDevice(). If you've reached the end of the data
(or if there is no I/O device set) atEnd() will return true. (or if there is no I/O device set) atEnd() will return true.
\section1 Serializing containers and strings
The serialization format is a length specifier first, then \a l bytes of data.
The length specifier is one quint32 if the version is less than 6.7 or if the
number of elements is less than 0xfffffffe (2^32 -2). Otherwise there is
an extend value 0xfffffffe followed by one quint64 with the actual value.
In addition for containers that support isNull(), it is encoded as a single
quint32 with all bits set and no data.
To take one example, if the string size fits into 32 bits, a \c{char *} string
is written as a 32-bit integer equal to the length of the string, including
the '\\0' byte, followed by all the characters of the string, including the
'\\0' byte. If the string size is greater, the value 0xffffffffe is written
as a marker of an extended size, followed by 64 bits of the actual size.
When reading a \c {char *} string, 4 bytes are read first. If the value is
not equal to 0xffffffffe (the marker of extended size), then these 4 bytes
are treated as the 32 bit size of the string. Otherwise, the next 8 bytes are
read and treated as a 64 bit size of the string. Then, all the characters for
the \c {char *} string, including the '\\0' terminator, are read.
\section1 Versioning \section1 Versioning
QDataStream's binary format has evolved since Qt 1.0, and is QDataStream's binary format has evolved since Qt 1.0, and is