Re: Semantic Checking - C

There is only so much heuristics can do. Better results can be had when
a bit of user annotation is added. Many project do this, Linus' sparse
checker is one such example.


It's quite common to write a general macros which when instantiated
results in unused variables, unreached code, lots of constant
expressions, etc. and without a richer annotation you going to get a lot
of false negatives, turning the warnings into a nusance rather than a
help (just like gcc moronic complaints about "a && b || c").


> Common semantic errors in C language:


A subset of them are considered static (syntax or type) errors and are
already caught be most compilers:


> 1. Use of function without function prototypes
  > 13. The number and types of arguments in a function call must be the
  > same as the number and types of the prototypes
  > 14. A return statement must not have a return value unless it appears
  > in the function prototype that is declared to return a value
  > 15. Break statements appear outside enclosing constructs where a break
  > statement may appear
  > 16. Elements of enumerated types are repeated
  > 17. Variable names appear in the same lexical scope
  > 18. Labels are repeated




These are nearly never occur statically:


> 3. Division by zero
  > 8. Subscript out of bounds




These are no always errors (think parameterizable programs). Some are
even very common (5 & 7)


  > 2. Code with no effect (dead code)
  > 4. Use of functions and variables which are defined but not used
  > 5. Use of functions and variables with defined arguments that are
  > never used
  > 6. Use of functions and variables that return either with or without
  > any assigned value
  > 7. Use of functions and variables that return values that are never
  > used
  > 9. Booleans that always evaluate true or evaluate false
  > 11. Statements that cannot be reached during execution
  > 12. No identifiers or variables are used twice in the same block or
  > scope


This is not an error, except maybe in 1st year students programs (the
"cannot be entered" is an instance of unreachable code ~ 2):


  > 10. Checking of infinite loops as well as loops that cannot be exited
  > or entered


Tommy

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