When is

Question

When is %destructor invoked in BISON? I have the following bison code:

%union{
    char * sval; 
    Variable * vval; 
} 

%token VARIABLE 
%token L         


        

Answer 1

From the Bison Manual:

Discarded symbols are the following:

• stacked symbols popped during the first phase of error recovery,
• incoming terminals during the second phase of error recovery,
• the current lookahead and the entire stack (except the current right-hand side symbols) when the parser returns immediately, and
• the start symbol, when the parser succeeds.

So if you don't hit an error, the %destructor will be called on the stack if you return immediately (call YYABORT or YYACCEPT), or it will call it on start symbol if parsing succeeds.

Answer 2

I figured out, that I should free() it after I perform the action, so for example

...
| String CONCAT String { $$ = concat($1,$3); free($1); free($3); }
...

That did the trick for me.