flex bison windows introduction

As I'm new to lexer and parser, so I'm trying to read and understand others code.

Here is the code i'm trying to use : https://gist.github.com/justjkk/436828

But it's giving me error. How can I resolve this?

E:\flex_bison_test>gcc lex.yy.c y.tab.c -o json.exe
json.l: In function 'yylex':
json.l:34:11: warning: assignment to 'YYSTYPE' {aka 'int'} from 'char *' makes integer from pointer without a cast [-Wint-conversion]
     yylval=strclone(yytext);
           ^
json.l:38:11: warning: assignment to 'YYSTYPE' {aka 'int'} from 'char *' makes integer from pointer without a cast [-Wint-conversion]
     yylval=strclone(yytext);
           ^
json.l: In function 'strclone':
json.l:82:15: warning: implicit declaration of function 'strlen' [-Wimplicit-function-declaration]
     int len = strlen(str);
               ^~~~~~
json.l:82:15: warning: incompatible implicit declaration of built-in function 'strlen'
json.l:82:15: note: include '<string.h>' or provide a declaration of 'strlen'
json.l:79:1:
+#include <string.h>
 %%
json.l:82:15:
     int len = strlen(str);
               ^~~~~~
json.l:84:5: warning: implicit declaration of function 'strcpy' [-Wimplicit-function-declaration]
     strcpy(clone,str);
     ^~~~~~
json.l:84:5: warning: incompatible implicit declaration of built-in function 'strcpy'
json.l:84:5: note: include '<string.h>' or provide a declaration of 'strcpy'
y.tab.c: In function 'yyparse':
y.tab.c:627:16: warning: implicit declaration of function 'yylex' [-Wimplicit-function-declaration]
 # define YYLEX yylex ()
                ^~~~~
y.tab.c:1272:16: note: in expansion of macro 'YYLEX'
       yychar = YYLEX;
                ^~~~~
y.tab.c:1540:7: warning: implicit declaration of function 'yyerror'; did you mean 'yyerrok'? [-Wimplicit-function-declaration]
       yyerror (YY_("syntax error"));
       ^~~~~~~
       yyerrok
json.y: At top level:
json.y:80:6: warning: conflicting types for 'yyerror'
 void yyerror (char const *s) {
      ^~~~~~~
y.tab.c:1540:7: note: previous implicit declaration of 'yyerror' was here
       yyerror (YY_("syntax error"));
       ^~~~~~~

E:\flex_bison_test>

Or these should remain as it is.

All the commands, I have given :

flex json.l
bison -dy json.y
gcc lex.yy.c y.tab.c -o json.exe

Solution

Simply:

#include <string.h>

in your flex definitions section on top of json.l should fix it for you.

There's also a Makefile in the repository you pointed to. Maybe you should use that. You don't seem to be generating the parser files properly. See comment below.

As for the remaining warnings:

warning: implicit declaration of function 'yyerror';
warning: implicit declaration of function 'yylex';

These can be easily fixed by adding declarations of yylex() and yyerror should be present in the bison prologue section at the top of your json.y:

%{
    int yylex();
    void yyerror(const char *s);
%}

As for these ones:

json.l:34:11: warning: assignment to 'YYSTYPE' {aka 'int'} from 'char *' makes integer from pointer without a cast [-Wint-conversion]
 yylval=strclone(yytext);
       ^
json.l:38:11: warning: assignment to 'YYSTYPE' {aka 'int'} from 'char *' makes integer from pointer without a cast [-Wint-conversion]
 yylval=strclone(yytext);
       ^

They're a bit more subtle. I would suggest have a look here on how to use yylval for correctly passing on strings from the lex's tokens into the parser's actions. The problem now is that yylval is a bare int but it ends up being assigned char pointers for both NUMBER and STRING tokens.