In case anyone needs the sample for a re-entrant lexer: int main(void) { yyscan_t scanner; YY_BUFFER_STATE buf; yylex_init(&scanner); buf = yy_scan_string(“replace me with the string youd like to scan”, scanner); yylex(scanner); yy_delete_buffer(buf, scanner); yylex_destroy(scanner); return 0; }
I’m a happy user of PLY. It is a pure-Python implementation of Lex & Yacc, with lots of small niceties that make it quite Pythonic and easy to use. Since Lex & Yacc are the most popular lexing & parsing tools and are used for the most projects, PLY has the advantage of standing on … Read more
Redefine YY_INPUT. Here’s a working example, compile and run with the commands yacc -d parser.y lex lexer.l gcc -o myparser *.c Input is read from globalInputText. You can modify this example so that global input text is whatever string you want or from any input source you want. parser.y: %{ #include <stdio.h> extern void yyerror(char* … Read more
A string consists of a quote mark ” followed by zero or more of either an escaped anything \\. or a non-quote character, non-backslash character [^”\\] and finally a terminating quote ” Put it all together, and you’ve got \”(\\.|[^”\\])*\” The delimiting quotes are escaped because they are Flex meta-characters.
The following routines are available for setting up input buffers for scanning in-memory strings instead of files (as yy_create_buffer does): YY_BUFFER_STATE yy_scan_string(const char *str): scans a NUL-terminated string` YY_BUFFER_STATE yy_scan_bytes(const char *bytes, int len): scans len bytes (including possibly NULs) starting at location bytes Note that both of these functions create, return a corresponding YY_BUFFER_STATE … Read more
As for today (2011-04-05, updated 2017-11-29) you will need the lastest versions of: flex-2.5.4a-1.exe bison-2.4.1-setup.exe After that, do a full install in a directory of your preference without spaces in the name. I suggest C:\GnuWin32. Do not install it in the default (C:\Program Files (x86)\GnuWin32) because bison has problems with spaces in directory names, not … Read more
Parsing C++ is extremely hard because the grammar is undecidable. To quote Yossi Kreinin: Outstandingly complicated grammar “Outstandingly” should be interpreted literally, because all popular languages have context-free (or “nearly” context-free) grammars, while C++ has undecidable grammar. If you like compilers and parsers, you probably know what this means. If you’re not into this kind … Read more