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Nick Mathewson authored
C99 allows a syntax for structures whose last element is of unspecified length: struct s { int elt1; ... char last_element[]; }; Recent (last-5-years) autoconf versions provide an AC_C_FLEXIBLE_ARRAY_MEMBER test that defines FLEXIBLE_ARRAY_MEMBER to either no tokens (if you have c99 flexible array support) or to 1 (if you don't). At that point you just use offsetof [STRUCT_OFFSET() for us] to see where last_element begins, and allocate your structures like: struct s { int elt1; ... char last_element[FLEXIBLE_ARRAY_MEMBER]; }; tor_malloc(STRUCT_OFFSET(struct s, last_element) + n_elements*sizeof(char)); The advantages are: 1) It's easier to see which structures and elements are of unspecified length. 2) The compiler and related checking tools can also see which structures and elements are of unspecified length, in case they wants to try weird bounds-checking tricks or something. 3) The compiler can warn us if we do something dumb, like try to stack-allocate a flexible-length structure.
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