Re: bison/flex: Best practice to report an libc error to caller of yyparse

[Hans Aberg]

On 13 Jun 2009, at 17:55, Nicolai Stange wrote:

> > > i wonder how to report an libc error
> > > (maybe ENOMEM, EIO) that has occured in either yylex or yyparse to  
> > > the
> > > caller of yyparse.
> >
> > As for the first error, memory allocation error, your program is
> > likely unrecoverable, so just write an error message and exit.
> There are three reasons why I don't want to do that.
> 1.) On EIO it could be possible for the program to continue, with some
> other file for example.

THat would not work on
  ENOMEM  (* Not enough memory *)

> 2.) Sometimes later on the parser could be incorporated within a  
> library
> and to my knowledge a library should not print any text if it's not  
> its
> particular intention.

Then you will have to take measures to turn off all other parser/lexer  
error messages. There is a difference between stdout and stderr, too.

> 3.) I want to have some general error handling mechanism,  
> independent of
> the actual libc error code or what else has happened.

You can use C++ and throw and catch exceptions. When generating a  
parser error, though, it will try to recover (see Bison manual).

> > For other errors, I had to write in .l:
> >   #define YYERRCODE     256
> What's the difference in using
> %token YYERRCODE
> that doesn't rely on bison internals instead?

When the Bison parser sees 256 (or so I remember), it will generate a  
parser error. When it sees %token YYERRCODE that is just a normal  
token, you still have to figure out how to generate an error in the  
parser.

  Hans