Question

I am currently working on a compiler under C and I am abit lost at the part where we construct the data structure for AST, especially for the part where we construct stucture for IDs, it is called “Symbol Table Entry”

I see structures over net such as:

struct ste {
  struct id   *name;  /* pointer into hash table for assoc. id */
  struct decl *decl;  /* pointer into symbol table for its decl */
  struct ste  *prev;  /* pointer to previous entry in symbol table */
}; 

It looks like a linked list as it holds a pointer to the previous entry (*prev) but what is the logic behind this ?

Answer 1

The answer to your concrete question is this: the prev link means that, when your code has a pointer to one of these node, it can follow the link to the previous link in the chain. One reason a symbol table might have a list like this is to deal with nested scope:

{
int x;
  {
   int x;
  }
}

However, there are many, many other reasons why the symbols nodes might want to be arranged in a list. Any reason why the compiler needs to visit all the nodes is a reason.