flex+bison一起使用的超简单例子

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/*definitions : alias re-string*/
%{
    #include <stdlib.h>
    #include <stdio.h>
    #include "bison.tab.h"
%}
number [0-9]+
%%
 
{number} {yylval = atoi(yytext);return NUM; }

[-+//*()^n]	{return *yytext;}

[ t]    ;

%%

/* 到达文件末尾的回调函数 */
int yywrap(void)
{
  /* We reached the end of the input file... */

  /* Should we continue with another file? */
  /* If so:
   *   open the new file...
   *   return 0;
   */

  /* to stop processing...
   *   return 1;
   */

  return 1;  /* Stop scanning at end of input file. */
}

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%{
  #define YYSTYPE int
  #include <math.h>
  #include <stdio.h>
  int yylex (void);
  void yyerror (char const *);
%}

%token NUM
%left '-' '+'
%left '*' '/'
%left NEG     /* negation--unary minus */ /* 负号 */
%right '^'    /* exponentiation */ /* 幂运算 */

%% /* The grammar follows.  */ /*　下面是语法 */
input:    /* empty */
        | input line
;

line:     'n'
        | exp 'n'  { 
            printf ("out:%dn", $1); 
            }
        | error 'n' { yyerrok;}
;

exp:      NUM                { $$ = $1;         }
        | exp '+' exp        { $$ = $1 + $3;    }
        | exp '-' exp        { $$ = $1 - $3;    }
        | exp '*' exp        { $$ = $1 * $3;    }
        | exp '/' exp        { $$ = $1 / $3;    }
        | '-' exp  %prec NEG { $$ = -$2;        }
        | exp '^' exp        { $$ = pow ($1, $3); }
        | '(' exp ')'        { $$ = $2;         }
;
%%



int main (void)
{
  return yyparse ();
}


/* Called by yyparse on error.  */
void yyerror (char const *s)
{
  fprintf (stderr, "error:%sn", s);
}

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bison -d bison.y  && flex flex.l && gcc *.c -w -lm && ./a.out