lexical analysis - Difference "Flex and Bison" code in windows and linux -

i working through sample code o'reilly press book entitled "flex , bison". using gnu c compiler windows flex , bison binary install windows launched using gcc rather linux cc command. problem code if copied directly book not compile , have had hack bit work.

example book

 example 1-1. word count fb1-1.l  /* unix wc */  %{  int chars = 0;  int words = 0;  int lines = 0;  %}  %%  [a-za-z]+ { words++; chars += strlen(yytext); }  \n { chars++; lines++; }  . { chars++; }  %% main(int argc, char **argv)  {  yylex();  printf("%8d%8d%8d\n", lines, words, chars);  } 

i compiled code in flowing way using windows command line: flex file.l gcc lex.yy.c -o a.exe

it crashed stating yywrap() not found. added , worked did not complete printf in main function hung waiting more input!

here solution works feels hack , not in full understanding of process.

    /* unix wc */  %{      *#include <string.h>*      int chars = 0;      int words = 0;      int lines = 0;  %}  %%  [a-za-z]+   { words++; chars += strlen(yytext); }  \n          { chars++; lines++; }  *"."         { return ;}*  .           { chars++; }   %%  *int yywrap(void) {     return 1; }*  int main(void)  {     yylex();      printf("num lines %8d, num words %8d, num chars %8d\n", lines, words, chars);      return 0;   } 

i had add new rule return out of yylex() not in book, add yywrap()- not knowing why , add string.h not present!. main question there significant differences between flex windows , unix , possible run original code gcc compiler , gnu flex without said hacks?

i not understand have achieved this:

#include <string.h>  "." { return; } 

but know sure if running flex without specified input file have mark end of input. otherwise flex wait input. suggest:

%{ #include <stdio.h> int chars = 0; int words = 0; int lines = 0; %} word        [a-za-z]+ %% {word}  {             words++;             chars += strlen(yytext);         } \n      {             lines++;             /* chars++; why this? there no columns here - it's new line */         } \s      {             /* count spaces */             chars++;         } \t      {             /* count tabs */             chars += 4 /* or 8 */;         } .       {             printf("error (unknown symbol):\t%c\n", yytext[0]);             chars++;         } %% int main() {     /* iterate until end of input , if errors - continue */     while(yylex()){ }     printf("lines:\t%8d\nwords:\t%8d\nchars:\t%8d\n", lines, words, chars);     return 0; } 

build with:

flex input.l 

output lex.yy.c build:

gcc -o scanner.exe lex.yy.c -lfl 

create txt file input. run following:

scanner.exe <in.txt>out.txt 

less sign means redirect input file in.txt while greater sign means redirect output out.txt cause file has eof @ end of file flex stop.