Re: how to handle large varible sized semanitc values (in C-based parsers)?

[Hans Aberg]

On 5 Jul 2007, at 03:27, Gary Funck wrote:

> Given the following semantic value definition:
>
> %union {
>   uda_tword_t val;
>   uda_tword_t val2[2];
>   uda_tint_t signed_val;
>   uda_taddr_t addr_val;
>   uda_debugger_pts_t pts;
>   char *str;
>   uda_binary_data_t *data;
> }
>
> where uda_binary_data_t is defined as:
>
> typedef uint8_t uda_byte_t;
> typedef struct uda_binary_data_struct
> {
>   size_t len;
>   uda_byte_t *bytes;
> } uda_binary_data_t;
>
> Above, data->bytes is an arbitrary sequence of bytes allocated
> via malloc.  In practice, a large maximum size (on the order of
> 16K bytes) could be established.  But if uda_binary_data_
> is redefined as:
>
> typedef struct uda_binary_data_struct
> {
>   size_t len;
>   uda_byte_t bytes[16*1024];
> } uda_binary_data_t;
>
> my understanding is that bison will copy this 16K byte value
> on each reduce operation.  Is that correct?

The Bison generated parser just implements %union as a C/C++ "union",  
which is copied as memory. So if you have put in a pointer into % 
union, as above, only the pointer will be copied. The rest will have  
to be implemented in the actions, and during error recovery, using % 
destructor (typically for cleanups).

  Hans Aberg