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/****************************************************************************
**
** Copyright (C) 2012 Digia Plc and/or its subsidiary(-ies).
** Contact: http://www.qt-project.org/legal
**
** This file is part of the documentation of the Qt Toolkit.
**
** $QT_BEGIN_LICENSE:FDL$
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**
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** Alternatively, this file may be used under the terms of the GNU Free
** Documentation License version 1.3 as published by the Free Software
** Foundation and appearing in the file included in the packaging of
** this file. Please review the following information to ensure
** the GNU Free Documentation License version 1.3 requirements
** will be met: http://www.gnu.org/copyleft/fdl.html.
** $QT_END_LICENSE$
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****************************************************************************/
/*!
\example xmlpatterns/xquery/globalVariables
\title C++ Source Code Analyzer Example
This example uses XQuery and the \c xmlpatterns command line utility to
query C++ source code.
\tableofcontents
\section1 Introduction
Suppose we want to analyze C++ source code to find coding standard
violations and instances of bad or inefficient patterns. We can do
it using the common searching and pattern matching utilities to
process the C++ files (e.g., \c{grep}, \c{sed}, and \c{awk}). Now
we can also use XQuery with the Qt XML Patterns module.
An extension to the \c{g++} open source C++ compiler
(\l{http://public.kitware.com/GCC_XML/HTML/Index.html} {GCC-XML})
generates an XML description of C++ source code declarations. This
XML description can then be processed by Qt XML Patterns using
XQueries to navigate the XML description of the C++ source and
produce a report. Consider the problem of finding mutable global
variables:
\section2 Reporting Uses of Mutable Global Variables
Suppose we want to introduce threading to a C++ application that
was originally written without threading. In a threaded program,
mutable global variables can cause bugs, because one thread might
change a global variable that other threads are reading, or two
threads might try to set the same global variable. So when
converting our program to use threading, one of the things we must
do is protect the global variables to prevent the bugs described
above. How can we use XQuery and
\l{http://public.kitware.com/GCC_XML/HTML/Index.html} {GCC-XML} to
find the variables that need protecting?
\section3 A C++ application
Consider the declarations in this hypothetical C++ application:
\snippet xmlpatterns/xquery/globalVariables/globals.cpp 0
\section3 The XML description of the C++ application
Submitting this C++ source to
\l{http://public.kitware.com/GCC_XML/HTML/Index.html} {GCC-XML}
produces this XML description:
\quotefromfile xmlpatterns/xquery/globalVariables/globals.gccxml
\printuntil
\section3 The XQuery for finding global variables
We need an XQuery to find the global variables in the XML
description. Here is our XQuery source. We walk through it in
\l{XQuery Code Walk-Through}.
\quotefromfile xmlpatterns/xquery/globalVariables/reportGlobals.xq
\printuntil
\section3 Running the XQuery
To run the XQuery using the \c xmlpatterns command line utility,
enter the following command:
\code
xmlpatterns reportGlobals.xq -param fileToOpen=globals.gccxml -output globals.html
\endcode
\section3 The XQuery output
The \c xmlpatterns command loads and parses \c globals.gccxml,
runs the XQuery \c reportGlobals.xq, and generates this report:
\div {class="details"}
Start report: 2008-12-16T13:43:49.65Z
\enddiv
Global variables with complex types:
\list 1
\li \span {class="variableName"} {mutableComplex1} in globals.cpp at line 14
\li \span {class="variableName"} {mutableComplex2} in globals.cpp at line 15
\li \span {class="variableName"} {constComplex1} in globals.cpp at line 16
\li \span {class="variableName"} {constComplex2} in globals.cpp at line 17
\endlist
Mutable global variables with primitives types:
\list 1
\li \span {class="variableName"} {mutablePrimitive1} in globals.cpp at line 1
\li \span {class="variableName"} {mutablePrimitive2} in globals.cpp at line 2
\endlist
\div {class="details"} End report: 2008-12-16T13:43:49.65Z \enddiv
\section1 XQuery Code Walk-Through
The XQuery source is in
\c{examples/xmlpatterns/xquery/globalVariables/reportGlobals.xq}
It begins with two variable declarations that begin the XQuery:
\quotefromfile xmlpatterns/xquery/globalVariables/reportGlobals.xq
\skipto declare variable
\printto (:
The first variable, \c{$fileToOpen}, appears in the \c xmlpatterns
command shown earlier, as \c{-param fileToOpen=globals.gccxml}.
This binds the variable name to the file name. This variable is
then used in the declaration of the second variable, \c{$inDoc},
as the parameter to the
\l{http://www.w3.org/TR/xpath-functions/#func-doc} {doc()}
function. The \c{doc()} function returns the document node of
\c{globals.gccxml}, which is assigned to \c{$inDoc} to be used
later in the XQuery as the root node of our searches for global
variables.
Next skip to the end of the XQuery, where the \c{<html>} element
is constructed. The \c{<html>} will contain a \c{<head>} element
to specify a heading for the html page, followed by some style
instructions for displaying the text, and then the \c{<body>}
element.
\quotefromfile xmlpatterns/xquery/globalVariables/reportGlobals.xq
\skipto <html xmlns
\printuntil
The \c{<body>} element contains a call to the \c{local:report()}
function, which is where the query does the "heavy lifting." Note
the two \c{return} clauses separated by the \e {comma operator}
about halfway down:
\quotefromfile xmlpatterns/xquery/globalVariables/reportGlobals.xq
\skipto declare function local:report()
\printuntil };
The \c{return} clauses are like two separate queries. The comma
operator separating them means that both \c{return} clauses are
executed and both return their results, or, rather, both output
their results. The first \c{return} clause searches for global
variables with complex types, and the second searches for mutable
global variables with primitive types.
Here is the html generated for the \c{<body>} element. Compare
it with the XQuery code above:
\quotefromfile xmlpatterns/xquery/globalVariables/globals.html
\skipto <body>
\printuntil </body>
The XQuery declares three more local functions that are called in
turn by the \c{local:report()} function. \c{isComplexType()}
returns true if the variable has a complex type. The variable can
be mutable or const.
\quotefromfile xmlpatterns/xquery/globalVariables/reportGlobals.xq
\skipto declare function local:isComplexType
\printuntil };
\c{isPrimitive()} returns true if the variable has a primitive
type. The variable must be mutable.
\quotefromfile xmlpatterns/xquery/globalVariables/reportGlobals.xq
\skipto declare function local:isPrimitive
\printuntil };
\c{location()} returns a text constructed from the variable's file
and line number attributes.
\quotefromfile xmlpatterns/xquery/globalVariables/reportGlobals.xq
\skipto declare function local:location
\printuntil };
*/
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