I think the Question is self sufficient. Is the syntax of C Language completely defined through Context Free Grammars or do we have Language Constructs which may require non-Context Free definitions in the course of parsing?
An example of non CFL construct i thought was the declaration of variables before their use. But in Compilers(Aho Ullman Sethi), it is stated that the C Language does not distinguish between identifiers on the basis of their names. All the identifiers are tokenized as 'id' by the Lexical Analyzer. If C is not completely defined by CFGs, please can anyone give an example of Non CFL construct in C?