Parse File using flex and bison -

i need parse following file using flex , bison:

new file

begin block blk_rowdec               name                          cell_rowdec               size                             uni_rowdecsize               iterate                                   itr_rows               direction                               lgdir_rowdec               strap                         strd1,strd3,strd2               wrap                          wrd1               via                                           viab,viac,viad    ends blk_rowdec   

i want read above file , write code

lex.l

%{ #include <iostream> #include <stdio.h> #include "yacc.tab.h" #define yy_decl extern "c" int yylex()  using namespace std; %}  dot             "." colon           ":" semicolon       ";" comma           "," angle_left      "<" angle_right     ">" @              "@" equal           "=" square_open     "[" square_close    [^\\]"]" openbrace       "\(" closebrace      "\)" quote           "\"" quote_open      "\"" quote_close     [^\\]"\"" space           " " tab             "\t" crlf            "\r\n" quoted_pair     "\\"[^\r\n] digit           [0-9] alpha           [a-za-z] qtext           [0-9a-za-z!#$%&'()*+,\-.\/:;<=>?@\[\]^_`{|}~]  %%  [a-za-z0-9]+            { yylval.sval = strdup(yytext); return tok_string; }  {space}*                    {return tok_space; }  ^{space}*name            {return tok_name; } {space}*size.*              {return tok_size; } {space}*iterate.*           {return tok_iterate; } {space}*direction.*     {return tok_direction; }  ^{crlf}                         { return tok_empty_line; }  {crlf}                          {}  .                               {}/* ignore unknown chars */ 

yacc.y

%{ #include <cstdio>  #include <cstring> #include <iostream> #include <stdio.h>  using namespace std;  extern "c" int yylex(); extern "c" file *yyin;  void yyerror(const char* s); %}  // symbols. %union {     char* sval; };  %token <sval> tok_name %token <sval> tok_size %token <sval> tok_string %token <sval> tok_iterate %token <sval> tok_direction %token <sval> tok_empty_line  %token tok_space   %%  str:     tok_space tok_name tok_space tok_string      {         cout << "value:" << $2 << "->" << $4;     }     ; %%  int main(void) {     file * pt = fopen("new file ", "r" );     if(!pt)     {     cout << "bad input.noexistant file" << endl;     return -1;     }     yyin = pt;         {         yyparse();     }while (!feof(yyin));       } void yyerror(const char *s) {    cout << "error. " << s << endl;     exit(-1);    } #include "lex.yy.c" 

first, try print second line of file not able print anything. please me do??

compilation done by:

flex lex.l bison -d yacc.y g++ yacc.tab.c -lfl -o scanner.exe 

it important knowing how debug parser. in first part of file, #define yydebug 1, , in main set yydebug = 1. allow see exact steps when run parser ant you'll know error is. knowing extrimely important, because mistakes hard find. debug program!

%{ #include <cstdio>  #include <cstring> #include <iostream> #include <stdio.h>  #define yydebug 1 // new  using namespace std;  extern "c" int yylex(); extern "c" file *yyin;  void yyerror(const char* s); %}  int main(){    yydebug = 1; // new   yyparse(); } 

also yylval.sval = strdup(yytext); after need check whether yylval.sval null, because strdup(yytext) first allocating memory, , after function copying string, strdup(yytext) return null if memory allocation fails.