[SOLVED] String buffer with flex and bison

King_DuckZ · 11-29-2011, 07:13 AM

Hello, I'm trying to write a parser for a simple custom language, and I decided to try the well-known combo flex/bison.
I found a lot of examples on how to use them, but I'm a bit confused on how to read data from memory instead than from a file.

From what I've seen, yy_scan_buffer is what I'm looking for. Now my question is: yy_scan_buffer is declared in the lexer file, but the main program will call yyparse, no? So how do I tell yyparse what buffer it should use? And even then, the parser has no prototypes for lexer's functions, so how do I call yy_scan_buffer from there?
I hope someone can help me!

firstfire · 11-29-2011, 11:11 AM

Hi.

Look here. `yy_switch_to_buffer()' is what you are looking for.

Example:

Code:

%%
[[:alnum:]]+	printf("[%s]\n", yytext);
%%
int main()
{
	char buf[] = "this is a test string\0\0";
	YY_BUFFER_STATE bs = yy_scan_buffer(buf, sizeof(buf));
	yy_switch_to_buffer(bs);
	yylex();
}

Flex can generate a header file with prototypes for you:

Code:

flex  --header-file=lex.h ex1.

This will produce `lex.h' file. You can include it and use `yy_switch_to_buffer()' etc. in bison file.

Hope this helps.

King_DuckZ · 11-30-2011, 03:08 AM

Thanks firstfire, that's exactly what I needed! I'll put that to good use

I don't know how to mark the thread as solved, tho. If I click edit I can't change the title anyways.

firstfire · 11-30-2011, 05:06 AM

Hi.

To mark thread as solved click on the 'Thread Tools' button on top of the page and then 'Mark as solved'.