Re: my problem is "$"

[Fernando Ferreira]

hoanglong1712 wrote:
> good day everyone
> i don't understand this source code, please help   
>
> char stemp[100]
>
> extern int yyleng
>
> strncpy(stemp,$1,yyleng)
>
>
> and here is my question :
>
>      why must we declare extern
>      what is yyleng
>      what is the role of $1 in the above function
>   
> that is all my questions .
> thank you for your kind attention 
>
>   
Hi, as it can be seen on the Flex Manual 
(http://www.gnu.org/software/flex/manual/html_mono/flex.html#SEC15), 
yyleng is a global variable generated by Flex that holds the size (in 
characters) of the currently matched token.

Without more details about the structure of your source code, there is 
no way exactly to tell why it must be declared as an external variable, 
but one can suppose that it is because you are linking against a foreign 
object, created by Flex, and yyleng is declared there, thus the 
necessity of the "extern" declaration.

$1, if you are using it inside an action, (as it is explained here: 
http://www.gnu.org/software/bison/manual/html_mono/bison.html#Actions), 
refers to the semantic value of the first symbol on the right hand side 
of the rule.

This particular snippet of source code seems to be copying the first 
token on the right side of the rule to the stemp variable, but without 
seeing more code, that is just speculation.

Hope it helps,

Fernando Ferreira