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CS 501

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CS 501

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  1. CS 501 Lint, Purify, and Coding Standards Eric Melin September 26,1999

  2. Lint • Lint is a semantic checker that identifies potential bugs in C programs • Lint is a mistake! • In the early days of C on UNIX complete semantic checking was removed from the C compiler as a design decision. This allowed for smaller, simpler, and faster compilers at the expense of potentially buggy code. • Lint exists on UNIX systems (but not LINUX) • Most modern ANSI C compilers include Lint semantic checking functionality but only some of Lint’s other features • Use Lint Early and Often!

  3. What does Lint Do? • Checks for consistency in function use across multiple files • Finds • bugs • non-portable code • wasteful code • Typical Bugs Detected include • Argument types transposed between function and call • Function with wrong number of arguments takes junk from stack • Variables being used before set or never used

  4. More about Lint • See Unix man page • OR “Checking C Programs with lint” By Ian F. Darwin

  5. Purify • Purify is a tool for locating runtime errors in a C/C++ program • Purify can find • Array bounds errors • Accesses through dangling pointers • Uninitialized memory reads • Memory allocation errors • Memory leaks • Purify is available on Windows and UNIX systems and is a product of Rational Software www.rational.com

  6. How Purify Works • Purify instruments a program by adding protection instructions around every load and store operation • When program is executed a viewer will be created to display errors as they happen • Purify is flexible and can be run standalone with any executable (written in C) or within a debugging environment like Visual Studio • Purify is customizable and can be set to ignore certain types of errors

  7. How to Use Purify • add purify command to link command • program: $(OBJS) purify [-option ...] $(CC) $(CFLAGS) -o\ program $(OBJS) $(LIBS) • OR run purify in Visual Studio • OR load file in purify executable

  8. Coding Standards • Why Have Coding Standards? • Greater consistency between multiple developers • Easier to develop and maintain • Saves time and money • The Prime Directive • Document every time you go against a standard • No standard is perfect for every application, but failure to comply with your standards requires a comment

  9. Ambler’s Law of Standards • Industry Standards > organizational standards > project standards > no standards • The more commonly accepted a standard the easier it is for team members to communicate • Invent standards when necessary, but don’t waste time creating something that you won’t be able to use later. • All languages have recommended coding standards available. It is well worth your effort to find and use industry standards • Push for organizational standards whenever possible

  10. Good Coding Style • Names • Use full English descriptors • Use mixed case to make names readable • Use abbreviations sparingly and consistently • Avoid long names • Avoid leading/trailing underscores • Documentation • Document the purpose of every variable • Document why something is done not just what

  11. Accessors • use getVar() and setVar() functions on all class variable unless class is being used solely as a data structure • Member Functions Documentation • What and why member function does what it does • Parameters / return value • How function modifies object • Preconditions /Postconditions • Concurrency issues • Restrictions • Internal Documentation • Control Structures • Why as well as what the code does • Difficult or complex code • Processing order

  12. Examples of Coding Standards • http://www.ambysoft.com/javaCodingStandards.html • http://www.swtech.com/java/codestd/ • http://ccs.hst.nasa.gov/ccspages/policies/standards/coding_standards.html • http://www.scriptics.com/doc/styleGuide.pdf