www.buslab.orgPB173 1/11
PB173 - Tématický vývoj aplikací v
C/C++ (podzim 2012)
Skupina: Aplikovaná kryptografie a bezpečné
programování
https://minotaur.fi.muni.cz:8443/pb173_crypto
Petr Švenda, svenda@fi.muni.cz
Konzultace: G201, Pondělí 16-16:50
www.buslab.orgPB173 2/11
Refactoring
Refactoring is process of restructuralization of
source code to make it easier to understand and
modify in future without changing its observable
behaviour.
No new functionality is added
Existing code is rewritten, split, erased and
otherwise modified to improve code quality
www.buslab.orgPB173 3/11
Refactoring (2)
Coding can be divided into two parts
● adding code for new functionality
● refactoring existing code
Refactoring is necessary to keep code maintainable
● spaghetti code will sooner or later consume more time to maintain
that to rewrite it
Be aware – code rewrite might introduce new bugs
Proper (automated) testing is required
● that’s why you have unit tests for!
● run these tests during refactoring
www.buslab.orgPB173 4/11
Refactoring – refactoring techniques
(De-)Composing methods properly
Moving code between modules/classes
Change data organization
Making conditional expressions simpler
Making API clearer
…
See http://sourcemaking.com/refactoring
● detailed explanation of many techniques with examples
● principles and practical tips how to solve problems
www.buslab.orgPB173 5/11
Code extraction into separate function
http://sourcemaking.com/refactoring/extract-method
Locate function doing multiple functionalities
Identify logical blocks of functionality
Create new function
● with name describing What not How
● move code there, replace by function call
● think about others also using new function
Take care of local variables
● pass them as function arguments
www.buslab.orgPB173 6/11
Additional explanation variable
http://sourcemaking.com/refactoring/introduce-
explaining-variable
Add additional well-named variable to hold
intermediate value
● even when such variable is not necessary in principle
Improve readability of code
Increase possibility for debugging
● you can watch and conditionally break on variable
www.buslab.orgPB173 7/11
Separate work done by single module/class
http://sourcemaking.com/refactoring/extract-class
Over the time, your module/class will grow
● one module/class is doing multiple functionalities
Violation of several design principles
Identify distinct functionalities
● usually set of methods and attributes responsible for
single functionality
Create new class(es) and move functions there
● separate interfaces for separate functionalities
● use multiple inheritance or aggregation to glue together
www.buslab.orgPB173 8/11
Refactoring - tools
Most of the work with refactoring is “manual”
● find out how to refactor and write simpler code
Tools can still help
● identify problematic areas (Code metrics,
SourceMonitor)
● provide call graph and data flow (Doxygen, VS Profiler)
● apply transformation consistently in all project files
www.buslab.orgPB173 9/11
Refactoring – tools (2)
No real build-in refact. tool for C/C++ in VS 2010
● requires complete understanding of C/C++ code by refactoring tool
Refactoring support for C/C++ in VS 2012
● http://www.kunal-chowdhury.com/2012/06/refactor-your-code-
easily-using-visual.html
3rd party add-ons like Visual Assist X / VSCommands
● not only refactoring support, but also code completition…
● http://www.agile-code.com/blog/list-of-visual-studio-code-
refactoring-tools/
NetBeans (and others) have refactoring support
● http://wiki.netbeans.org/Refactoring
● variable renaming, code extraction…
www.buslab.orgPB173 10/11
Source monitor
Create new project
● File → New project
● language, directory with sources *.c / *.cpp
● initial ‘Baseline’
After code update
● Checkpoint → New checkpoint
Details on particular checkpoint and file
● RClick → Display Function Metrics Details...
www.buslab.orgPB173 11/11
Source monitor – example outputs
Complexity: 1-10 (OK), 11-20 (sometimes), > 20
(BAD)
www.buslab.orgPB173 12/11
Antipatterns
Common defective process and implementation
within organization
Opposite to design patterns
● see http://sourcemaking.com/design_patterns
Read http://sourcemaking.com/antipatterns
● good description, examples and how to solve
Not limited to object oriented programming!
Software development antipatterns
● http://sourcemaking.com/antipatterns/software-
development-antipatterns
www.buslab.orgPB173 13/11
Practical assignment - refactoring
Use code metric tool to analyze your sources
● http://www.campwoodsw.com/sourcemonitor.html
Find and refactor all functions
● with complexity more then 15
● with Maximum Depth more then 4
Read and use refactoring techniques
● http://sourcemaking.com/refactoring