How to compile LEX/YACC files on Windows?

As for today (2011-04-05, updated 2017-11-29) you will need the lastest versions of:

  1. flex-2.5.4a-1.exe
  2. bison-2.4.1-setup.exe
  3. 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 to say parenthesis.
  4. Also, consider installing Dev-CPP in the default directory (C:\Dev-Cpp)
  5. After that, set the PATH variable to include the bin directories of gcc (in C:\Dev-Cpp\bin) and flex\bison (in C:\GnuWin32\bin). To do that, copy this: ;C:\Dev-Cpp\bin;C:\GnuWin32\bin and append it to the end of the PATH variable, defined in the place show by this figure:
    step-by-step to set PATH variable under Win-7.
    If the figure is not in good resolution, you can see a step-by-step here.
  6. Open a prompt, cd to the directory where your “.l” and “.y” are, and compile them with:
    1. flex hello.l
    2. bison -dy hello.y
    3. gcc lex.yy.c -o hello.exe
Commands to create lexical analyzer, parser and executable.

You will be able to run the program. I made the sources for a simple test (the infamous Hello World):



#include ""
int yyerror(char *errormsg);



("hi"|"oi")"\n"       { return HI;  }
("tchau"|"bye")"\n"   { return BYE; }
.                     { yyerror("Unknown char");  }


int main(void)
   return 0;

int yywrap(void)
   return 0;

int yyerror(char *errormsg)
    fprintf(stderr, "%s\n", errormsg);



#include <stdio.h>
#include <stdlib.h>
int yylex(void);
int yyerror(const char *s);


%token HI BYE


         hi bye

        HI     { printf("Hello World\n");   }
        BYE    { printf("Bye World\n"); exit(0); }

Edited: avoiding “warning: implicit definition of yyerror and yylex”.

Disclaimer: remember, this answer is very old (since 2011!) and if you run into problems due to versions and features changing, you might need more research, because I can’t update this answer to reflect new itens. Thanks and I hope this will be a good entry point for you as it was for many.

Updates: if something (really small changes) needs to be done, please check out the official repository at github:

Happy hacking.

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