Help with yacc/compiler design/seg fault

This is a discussion on Help with yacc/compiler design/seg fault within the C Programming forums, part of the General Programming Boards category; I am taking a compiler design course and we are using yacc and lex for the parser and scanner. I ...

  1. #1
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    Join Date
    Oct 2004
    Posts
    32

    Help with yacc/compiler design/seg fault

    I am taking a compiler design course and we are using yacc and lex for the parser and scanner. I keep getting a seg fault in an unexpected place and I was wondering if anyone here could help me track down the problem.

    I will just post the .y file and the tree.c files for now because they are long, but I can post more if need be.

    When I use gdb to track down the seg fault, it tells me that the problem is with my .y file, in line 74, which is the { $1->next = $3; $$ = $1; } section of the state_decls production. I cannot figure out why there is a problem here, and I could use some advice, even if that advice is just a better way to find the source of my problem.

    The .y file:
    Code:
    %{
    #include "tree.h"
    
    extern tree root;
    tree BuildTree(int, tree, tree, tree);
    tree BuildIntTree(int, int);
    tree BuildFloatTree(int, float);
    %}
    
    %token <i>	Ident 1 IntConst 2 
    %token <f>	RealConst 3
    %token 		Var 11 Int 12 Real 13 Boolean 14 Record 15
    %token 		End 16 Bind 17 To 18 Assert 19 Begin 20
    %token 		Loop 21 Exit 22 When 23 If 24 Then 25
    %token 		Elsif 26 Else 27 Put 28 Or 29 And 30
    %token 		Not 31 NotEq 32 Div 33 Mod 34
    %token 		SemiColon 40 Colon 41 Assign 42 Gt 43 Lt 44
    %token 		Eq 45 Lte 46 Gte 47 Plus 48 Minus 49
    %token 		Star 50 Slash 51 Dot 52 Comma 53 LParen 54 RParen 55
    
    %start program
    
    %union { tree t; int i; float f; }
    
    %type <t>	program pStateDeclSeq id_list type field_list state_decls
    %type <t>	declaration statement ref end_if expr and_expr not_expr
    %type <t>	rel_expr sum prod factor basic
    
    %%
    
    program
    	: pStateDeclSeq
    		{ root = $1; }
    	;
    
    pStateDeclSeq
    	: /* nullable */
    		{ $$ = NULL; }
    	| statement SemiColon pStateDeclSeq
    		{ $1->next = $3; $$ = $1; }
    	| Var id_list Colon type SemiColon pStateDeclSeq
    		{ $$ = BuildTree(Var, $2, $4, $6); }
    	;
    
    id_list
    	: Ident
    		{ $$ = BuildIntTree(Ident, $1); }
    	| Ident Comma id_list
    		{ $$ = BuildTree(Comma, BuildIntTree(Ident, $1), $3, NULL); }
    	;
    
    type
    	: Int
    		{ $$ = BuildIntTree(Int, $<i>1); }
    	| Real
    		{ $$ = BuildFloatTree(Real, $<f>1); }
    	| Boolean
    		{ $$ = BuildIntTree(Boolean, $<i>1); }
    	| Record field_list End Record
    		{ $$ = BuildTree(Record, $2, BuildTree(End, NULL, NULL, NULL), BuildTree(Record, NULL, NULL, NULL)); }
    	;
    
    field_list
    	: id_list Colon type
    		{ $$ = BuildTree(Colon, $1, $3, NULL); }
    	| id_list Colon type SemiColon field_list
    		{ $$ = BuildTree(Colon, $1, $3, $5); }
    	;
    
    state_decls
    	: /* nullable */
    		{ $$ = NULL; }
    	| statement SemiColon pStateDeclSeq
    		{ $1->next = $3; $$ = $1; }
    	| declaration SemiColon pStateDeclSeq
    		{ $1->next = $3; $$ = $1; }
    	;
    
    declaration
    	: Var id_list Colon type
    		{ $$ = BuildTree(Var, $2, $4, NULL); }
    	| Bind Ident To ref
    		{ $$ = BuildTree(Bind, BuildIntTree(Ident, $2), BuildTree(To, $4, NULL, NULL), NULL); }
    	| Bind Var Ident To ref
    		{ $$ = BuildTree(Bind, BuildTree(Var, BuildIntTree(Ident, $3), NULL, NULL), BuildTree(To, $5, NULL, 
    NULL), NULL); }
    	;
    
    statement
    	: ref Assign expr
    		{ $$ = BuildTree(Assign, $1, $3, NULL); }
    	| Assert expr
    		{ $$ = BuildTree(Assert, $2, NULL, NULL); }
    	| Begin state_decls End
    		{ $$ = BuildTree(Begin, $2, BuildTree(End, NULL, NULL, NULL), NULL); }
    	| Loop state_decls End Loop
    		{ $$ = BuildTree(Loop, $2, BuildTree(End, NULL, NULL, NULL), BuildTree(Loop, NULL, NULL, NULL)); }
    	| Exit
    		{ $$ = NULL; }
    	| Exit When expr
    		{ $$ = BuildTree(Exit, BuildTree(When, $3, NULL, NULL), NULL, NULL); }
    	| If expr Then state_decls end_if
    		{ $$ = BuildTree(If, $2, BuildTree(Then, $4, $5, NULL), NULL); }
    	;
    
    ref
    	: Ident
    		{ $$ = BuildIntTree(Ident, $1); }
    	| Ident Dot Ident
    		{ $$ = BuildTree(Dot, BuildIntTree(Ident, $1), BuildIntTree(Ident, $3), NULL); }
    	;
    
    end_if
    	: End If
    		{ $$ = NULL; }
    	| Else state_decls End If
    		{ $$ = BuildTree(Else, $2, NULL, NULL); }
    	| Elsif expr Then state_decls end_if
    		{ $$ = BuildTree(Elsif, $2, $4, $5); }
    	;
    
    expr
    	: expr Or and_expr
    		{ $$ = BuildTree(Or, $1, $3, NULL); }
    	| and_expr
    		{ $$ = $1; }
    	;
    
    and_expr
    	: and_expr And not_expr
    		{ $$ = BuildTree(And, $1, $3, NULL); }
    	| not_expr
    		{ $$ = $1; }
    	;
    
    not_expr
    	: Not not_expr
    		{ $$ = BuildTree(Not, $2, NULL, NULL); }
    	| rel_expr
    		{ $$ = $1; }
    	;
    
    rel_expr
    	: sum
    		{ $$ = $1; }
    	| rel_expr Eq sum
    		{ $$ = BuildTree(Eq, $1, $3, NULL); }
    	| rel_expr NotEq sum
    		{ $$ = BuildTree(NotEq, $1, $3, NULL); }
    	| rel_expr Lt sum
    		{ $$ = BuildTree(Lt, $1, $3, NULL); }
    	| rel_expr Lte sum
    		{ $$ = BuildTree(Lte, $1, $3, NULL); }
    	| rel_expr Gt sum
    		{ $$ = BuildTree(Gt, $1, $3, NULL); }
    	| rel_expr Gte sum
    		{ $$ = BuildTree(Gte, $1, $3, NULL); }
    	;
    
    sum
    	: prod
    		{ $$ = $1; }
    	| sum Plus prod
    		{ $$ = BuildTree(Plus, $1, $3, NULL); }
    	| sum Minus prod
    		{ $$ = BuildTree(Minus, $1, $3, NULL); }
    	;
    
    prod
    	: factor
    		{ $$ = $1; }
    	| prod Star factor
    		{ $$ = BuildTree(Star, $1, $3, NULL); }
    	| prod Slash factor
    		{ $$ = BuildTree(Slash, $1, $3, NULL); }
    	| prod Div factor
    		{ $$ = BuildTree(Div, $1, $3, NULL); }
    	| prod Mod factor
    		{ $$ = BuildTree(Mod, $1, $3, NULL); }
    	;
    
    factor
    	: Plus basic
    		{ $$ = BuildTree(Plus, $2, NULL, NULL); }
    	| Minus basic
    		{ $$ = BuildTree(Minus, $2, NULL, NULL); }
    	| basic
    		{ $$ = $1; }
    	;
    
    basic
    	: ref
    		{ $$ = $1; }
    	| LParen expr RParen
    		{ $$ = $2; }
    	| IntConst
    		{ $$ = BuildIntTree(IntConst, $1); }
    	| RealConst
    		{ $$ = BuildFloatTree(RealConst, $1); }
    	;
    
    %%
    The tree.c file:
    Code:
    #include <stdlib.h>
    #include "tree.h"
    
    tree BuildTree(int k, tree f1, tree s2, tree t3)
    {
    	tree t;
    	t = (tree)malloc(sizeof(node));
    
    	t->kind = k;
    	t->first = f1;
    	t->second = s2;
    	t->third = t3;
    	t->next = NULL;
    
    	return t;
    }
    
    tree BuildIntTree(int k, int v)
    {
    	tree t;
    	t = (tree)malloc(sizeof(node));
    	
    	t->kind = k;
    	t->value = v;
    	t->first = NULL;
    	t->second = NULL;
    	t->third = NULL;
    	t->next = NULL;
    
    	return t;
    }
    
    tree BuildFloatTree(int k, float v)
    {
    	tree t;
    	t = (tree)malloc(sizeof(node));
    
    	t->kind = k;
    	t->value = v;
    	t->first = NULL;
    	t->second = NULL;
    	t->third = NULL;
    	t->next = NULL;
    
    	return t;
    }
    
    void PrintTree(tree t, int indent)
    {
    	int i;
    	char str[]="--|";
    
    	if(t != NULL)
    	{
    		printf("%d\n", t->value);
    		PrintTree(t->first, indent+1);
    		PrintTree(t->second, indent+1);
    		PrintTree(t->third, indent+1);
    	}
    }

  2. #2
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    Join Date
    Sep 2004
    Posts
    719
    Code:
    { $1->next = $3; $$ = $1; }
    if i had to bet, i would say you're trying to access memory that's not there
    and that $1->next == NULL
    i seem to have GCC 3.3.4
    But how do i start it?
    I dont have a menu for it or anything.

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