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Improve the documentation of QStringLiteral

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Change-Id: I4bbe18ecc342f034fbc8e9fd14b700ee5272076f
Reviewed-by: Denis Dzyubenko <denis.dzyubenko@nokia.com>
Reviewed-by: Robin Burchell <robin+qt@viroteck.net>
This commit is contained in:
Olivier Goffart 2012-01-13 18:29:31 +01:00 committed by Qt by Nokia
parent 51cb2dd00a
commit a03b4e4417
1 changed files with 27 additions and 3 deletions
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30
src/corelib/tools/qstring.cpp
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@ -8808,13 +8808,37 @@ QString QString::toHtmlEscaped() const
Creating a QString from it is free in this case, and the generated string data is stored in
the read-only segment of the compiled object file.
For compilers not supporting the creation of compile time strings, QStringLiteral will fall back to
QLatin1String.
The result of the QStringLiteral expression can be cast into a QString.
If you have code looking like:
\code
if (node.hasAttribute("http-contents-length")) //...
\endcode
One temporary QString will be created to be passed as the hasAttribute function parameter.
This can be quite expensive, as it involves a memory allocation and the copy and the conversion
of the data into QString's internal encoding.
This can be avoided by doing
\code
if (node.hasAttribute(QStringLiteral("http-contents-length"))) //...
\endcode
Then the QString's internal data will be generated at compile time and no conversion or allocation
will occur at runtime
Using QStringLiteral instead of a double quoted ascii literal can significantly speed up creation
of QString's from data known at compile time.
If the compiler is c++0x enabled the string \a str can actually contain unicode data.
If the compiler is C++11 enabled the string \a str can actually contain unicode data.
For compilers not supporting the creation of compile time strings, QStringLiteral will fall back to
QLatin1String.
\note There are still a few cases in which QLatin1String is more efficient than QStringLiteral:
If it is passed to a function that has an overload that takes the QLatin1String directly, without
conversion to QString. For instance, this is the case of QString::operator==
\code
if (attribute.name() == QLatin1String("http-contents-length")) //...
\endcode
*/
QT_END_NAMESPACE