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6.1 Syntactic classes

Generally speaking, the syntactic class of a symbol defines where in the C code this symbol can legitimately appear. There are following classes:

A keyword, like ‘if’, ‘when’ etc.
Type modifier, i.e. the symbol appearing after a data type to modify its meaning, like ‘*’.
Declaration qualifier. Can appear both before C declaration (much like ‘static’ or ‘extern’) and after a data type (like modifiers).

You would usually declare a gcc keyword ‘__extension__’ as a qualifier:

          --symbol __extension__:qualifier

A C identifier.
A C data type, like ‘int’, ‘char’, etc.
That has two meanings. First, it can be used to declare parameter wrappers when running cflow without preprocessor. This usage was described above. Second, it indicates any symbol that can appear in a declaration either before an identifier or before a terminating semicolon and optionally followed by a parenthesized expression list.

We recommended to use this class for the gcc__attribute__’ keyword.