CODEWITHSUNDEEP
cgdbyaccbison
Kyle Brandt
Kyle Brandt

Reputation: 28407

Inspect Bison's $$ variable with GDB

If I set a breakpoint in a Bison .y file, is there a way I can inspect the contents of $$ pseudo variable at that breakpoint?

Upvotes: 2

Views: 1404

Answers (3)

Ryan Li
Ryan Li

Reputation: 9330

I redefined the type of yylval with %union:

%union {
  int int_val;
  double double_val;
}

And what I get is either yyval.int_val or yyval.double_val depending on the type of $$.

But just as Richard Pennington said, the best way would be to look at the generated .tab.c code.

Upvotes: 0

DigitalRoss
DigitalRoss

Reputation: 146073

Bison keeps the stacks as local variables in yyparse(), dynamically allocated.

Probably the easiest way to solve a temporary debugging issue is to patch y.tab.c so that the line *++yyvsp = yylval also drops a copy in a global. You may also want to hack YYPOPSTACK() to do the same thing.

Upvotes: 2

Richard Pennington
Richard Pennington

Reputation: 19965

$$ is be the top of the semantic value stack. It may be a little difficult to interpret. If you really need to, the stack pointer might be called yyssp and the stack might be called yyvsa, so something like yyvsa[yyssp] might give you what you want, depending on the version of bison you're using. Look at .tab.c code that was generated.

Upvotes: 5

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