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authorOlivier Goffart <ogoffart@woboq.com>2012-01-13 18:29:31 +0100
committerQt by Nokia <qt-info@nokia.com>2012-01-16 03:51:14 +0100
commita03b4e441760e401f1aeb38d500c9cf71bdf199e (patch)
tree358a9f9a6f1c6edb251babe13b44dd833eb10eb3 /src
parent51cb2dd00ae16d5e5a1be1ae02fafdc2ed3641d7 (diff)
Improve the documentation of QStringLiteral
Change-Id: I4bbe18ecc342f034fbc8e9fd14b700ee5272076f Reviewed-by: Denis Dzyubenko <denis.dzyubenko@nokia.com> Reviewed-by: Robin Burchell <robin+qt@viroteck.net>
Diffstat (limited to 'src')
-rw-r--r--src/corelib/tools/qstring.cpp30
1 files changed, 27 insertions, 3 deletions
diff --git a/src/corelib/tools/qstring.cpp b/src/corelib/tools/qstring.cpp
index eea41ea3d7..1b6ff3c5df 100644
--- a/src/corelib/tools/qstring.cpp
+++ b/src/corelib/tools/qstring.cpp
@@ -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