Short answer: yylval.strval = yytext; You can’t use yytext like that. The string it points to is private to the lexer and will change as soon as the flex action finishes. You need to do something like: yylval.strval = strdup(yytext); and then you need to make sure you free the memory afterwards. Longer answer: yytext … Read more
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
1. Sample code A kind of explanation of how reentrancy is configured into bison and flex is provided in section 2 of this answer. Other annotations of the sample code are in section 3. 1.1 eval.l %option noinput nounput noyywrap 8bit nodefault %option yylineno %option reentrant bison-bridge bison-locations %{ #include <stdlib.h> #include <string.h> #include “eval.tab.h” … Read more
There is a much simpler solution. If you know how LR parsers work, then you know that the conflict happens here: if ( expression ) statement * else statement where the star marks the current position of the cursor. The question the parser must answer is “should I shift, or should I reduce”. Usually, you … Read more
If you want an easy way to code parsers, or you are tight on space, you should hand-code a recursive descent parser; these are essentially LL(1) parsers. This is especially effective for languages which are as “simple” as Basic. (I did several of these back in the 70s!). The good news is these don’t contain … Read more