On 13/09/2012 22:52, Oleksii Taran wrote:
13.09.12 19:32, Hans Aberg wrote:
On 13 Sep 2012, at 17:54, Oleksii Taran wrote:
Does Bison guarantees exception safety in C++ parser, i.e. will it make
any clean-up and free memory if an exception is thrown on rule action?
Yes, the default stack is std::deque.
I
know about %destructor directive, but it seems irrelevant, since
destructor code is called only if parser recovers from _syntax_ error.
This is for the C parser, since C does not provide automatic cleanup. I might
be possible to compile this parser as C++ (supported at least in the past), in
which case %destructor would be needed.
If "C" the parser doesn't recover from a syntax error context (i.e. the
code is syntactically correct), you have to free yourself the memory. I
just suggest to create a simple tree inside the actions, and to free it
from the leaves up to the root. When a syntax error happens instead, you
have to free many sub-trees.
Please keep also into account that freeing memory is really needed only
when you design an interactive always running parser, like a command
line one; for a "batch" compiler the memory will be freed when the
process will exit.
But what if deque holds not objects, but pointers to them? e.g. code
like this:
%union {
::std::string *token;
}
How Bison knows that it should call something like `delete token;` ?
Using %destructor you can specify the action (delete) and the production
to apply, for example:
%destructor{delete $$} exp stmt
since $$ is a
::std::string *token;
for "exp" and "stmt".
Also using "C", you can always put a void* inside the union.
Luca
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