How to define grammar which excludes a certain set of words?

I have built a small code for static analysis of C code. The purpose of building it is to warn users about the use of methods such as strcpy() which could essentially cause buffer overflows.

Now, to formalise the same, I need to write a formal Grammar which shows the excluded libraries as NOT a part of the allowed set of accepted library methods used.

For example,

AllowedSentence->ANSI C Permitted Code, NOT UnSafeLibraryMethods

UnSafeLibraryMethods->strcpy|o开发者_JAVA百科ther potentially unsafe methods

Any ideas on how this grammar can be formalised?

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I think, this should not be done at the grammar level. It should be a rule that is applied to the parse tree after parsing is done.

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You hardly need a parser for the way you have posed the problem. If your only goal is to object to the presence of certain identifiers ("strcpy"), you can simply build a lexer that processes C and picks identifiers. Special lexemes can recognize your list of "you shouldn't use this". This way you use positive recognition instead of negative recognition to pick out the identifiers that you belive to be trouble.

If you want a more sophisticated analaysis tool, you'll likely want to parse C, an name-resolve the identifers to their actual definitisn, then the scan the tree looking for identifiers that are objectionable. This will at least let you decide if the identifier is actually defined by the user, or comes from some known library; surely, if my code defines strcpy, you shouldn't complain unless you know my strcpy is defective somehow.