How to organize the data structure in a parser?

Hi, all


I am trying to design a parser for C program using C++. Currently what
I did for syntax tree is to design a class for each nontermials in the
grammar, and use inherentance to link them. For example, as for the
expression part, the classes are something like the follows:


....
class MultiplicativeExpr : public AdditiveExpr
{
MultiplicativeExpr * multi_expr;
int op_type;
PmExpr * pm_expr;
};


class AdditiveExpr : public ShiftExpr
{
int op_type;
AdditiveExpr * additive_expr;
MultiplicativeExpr * multi_expr;
};


class ShiftExpr : public RelationalExpr
{
int op_type;
ShiftExpr * shift_expr;
AdditiveExpr * additive_expr;
};


class RelationalExpr : public EqualityExpr
{
int op_type;
RelationalExpr * relational_expr;
ShiftExpr * shift_expr;
};


....


I noticed that the bad thing about this solution is that using
inheritance, the children in the leaf of inheritance tree will be of
large size because it comprised of all data fields of its ancestors.
How can I organize the data structure more efficienty? Thanks a lot!


Andy

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