C++ Source Code Analyzer Example

Using XQuery and the xmlpatterns command line utility to query C++ source code.

This example uses XQuery and the xmlpatterns command line utility to query C++ source code.


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., grep , sed , and awk ). Now we can also use XQuery with the Qt XML Patterns module.

An extension to the g++ open source C++ compiler ( 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:

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 GCC-XML to find the variables that need protecting?

A C++ application

Consider the declarations in this hypothetical C++ application:

 1. int mutablePrimitive1;
 2. int mutablePrimitive2;
 3. const int constPrimitive1 = 4;
 4. const int constPrimitive2 = 3;
 6. class ComplexClass
 7. {
 8.  public:
 9.    ComplexClass();
10.    ComplexClass(const ComplexClass &);
11.    ~ComplexClass();
12. };
14. ComplexClass mutableComplex1;
15. ComplexClass mutableComplex2;
16. const ComplexClass constComplex1;
17. const ComplexClass constComplex2;
19. int main()
20. {
22.     int localVariable;
23.     localVariable = 0;
24.     return localVariable;
25. }

The XML description of the C++ application

Submitting this C++ source to GCC-XML produces this XML description:

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 XQuery Code Walk-Through .

Running the XQuery

To run the XQuery using the xmlpatterns command line utility, enter the following command:

xmlpatterns reportGlobals.xq -param fileToOpen=globals.gccxml -output globals.html

The XQuery output

The xmlpatterns command loads and parses globals.gccxml , runs the XQuery reportGlobals.xq , and generates this report:

Start report: 2008-12-16T13:43:49.65Z

Global variables with complex types:

  1. mutableComplex1 in globals.cpp at line 14

  2. mutableComplex2 in globals.cpp at line 15

  3. constComplex1 in globals.cpp at line 16

  4. constComplex2 in globals.cpp at line 17

Mutable global variables with primitives types:

  1. mutablePrimitive1 in globals.cpp at line 1

  2. mutablePrimitive2 in globals.cpp at line 2

End report: 2008-12-16T13:43:49.65Z

XQuery Code Walk-Through

The XQuery source is in examples/xmlpatterns/xquery/globalVariables/reportGlobals.xq It begins with two variable declarations that begin the XQuery :

The first variable, $fileToOpen , appears in the xmlpatterns command shown earlier, as -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, $inDoc , as the parameter to the doc() function. The doc() function returns the document node of globals.gccxml , which is assigned to $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 <html> element is constructed. The <html> will contain a <head> element to specify a heading for the html page, followed by some style instructions for displaying the text, and then the <body> element.

The <body> element contains a call to the local:report() function, which is where the query does the “heavy lifting.” Note the two return clauses separated by the comma operator about halfway down:

The return clauses are like two separate queries. The comma operator separating them means that both return clauses are executed and both return their results, or, rather, both output their results. The first 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 <body> element. Compare it with the XQuery code above:

The XQuery declares three more local functions that are called in turn by the local:report() function. isComplexType() returns true if the variable has a complex type. The variable can be mutable or const.

isPrimitive() returns true if the variable has a primitive type. The variable must be mutable.

location() returns a text constructed from the variable’s file and line number attributes.

Example project @ code.qt.io