带flex的词法分析器

Question

I am trying to build a lexical analyzer for a small language using flex.

The lexical will read a text file of lexemes and give each lexeme a token and write the token in another file. the code was able to open the file and read from it using yylex() function.

The problem is the code did not write the tokens in the specified file. Also I've found, that the code can not recognize numbers and gives each letter of an identifier an IDENTIFIER token I tried many methods to overcome these problem and I used ac language websites to write a correct C code.

A small notice is that I do not want to use a .y parser who read the lexeme and pass it to the lexical I want my lexical to read the token by it self and produce the token.

So can any one help me to fine what is the problem?

%{
#include<stdlib.h>
#include<conio.h>
#include<stdio.h>
#define KEY_INT 259
#define KEY_VOID 258
#define KEY_INT 259
#define KEY_FLOAT 260
#define KEY_IF 261
#define KEY_ELSE 262
#define KEY_WHILE 263
#define KEY_FOR 264
#define KEY_RETURN 265
#define KEY_BREAK 266
#define AND_OP 267
#define OR_OP 268
#define SMALL_EQ_OP 269
#define GREAT_EQ_OP 270
#define EQ_OP 271
#define SMALL_OP 272
#define GREAT_OP 273
#define NOT_EQ_OP 274
#define ASSIGN_OP 275
#define OPN__BRACKET 276
#define CLS__BRACKET 277
#define SEMICOLON_SYMBOL 278
#define COMMA_SYMBOL 279
#define DOT_SYMBOL 280
#define ADD_OP 281
#define SUB_OP 282
#define ASTERISK_SYMBOL 283
#define SLASH_SYMBOL 284
#define INT_NUM 287
#define FLOAT_NUM 288
#define IDENTIFIER 289
int yylval;
FILE *yyin,*yyout;
int c;
%}
Letters     [a-zA-Z]
Digits      [0-9]
Sympols     [@#$%&*-+!"':;/?(),~`|^_=×{}<>]
%%
[/*][{Letters}|{Digits}|{Sympols}|\n|\t ]*[*/]      {}  
[-+]?[{Digits}]+            {yylval = atoi(yytext); return INT_NUM ;}
[-+]?[{Digits}]+.[{Digits}]+        {yylval = atoi(yytext);return FLOAT_NUM ;}
{Letters}[{Letters}|{Digits}|_]*    {return IDENTIFIER ;}
[\t\n ]+    {}
"void"      {return KEY_VOID ;}
"float"     {return KEY_FLOAT ;}
"if"        {printf( "KEY_IF\n") ;}
"else"      {return KEY_ELSE ;}
"while"     {return KEY_WHILE ;}
"for"       {return KEY_FOR ;}
"return"    {return KEY_RETURN ;}
"break"     {return KEY_BREAK ;}
"&&"        {return AND_OP ;}
"||"        {return OR_OP ;}
"<="        {return SMALL_EQ_OP ;}
">="        {return GREAT_EQ_OP ;}
"=="        {return EQ_OP ; }
"<"     {return SMALL_OP ;}
">"     {return GREAT_OP ;}
"!="        {return NOT_EQ_OP ;}
"="     {return ASSIGN_OP ;}
"("     {return OPN__BRACKET ;}
")"     {return CLS__BRACKET ;}
";"     {return SEMICOLON_SYMBOL ;}
","     {return COMMA_SYMBOL ;}
"."     {return DOT_SYMBOL ;}
"+"     {return ADD_OP ;}
"-"     {return SUB_OP ;}
"*"     {return ASTERISK_SYMBOL ;}
"/"     {return SLASH_SYMBOL ;}
.       {yyerror() ;}
%%
int yyerror (void)
{
printf("Invalid input\n");
exit(1);
}
int yywrap()
{
return 1;
}
main()
{
if((yyin=fopen("C:\\ProCompFlex\\GnuWin32\\bin\\input.txt","r"))==NULL)
{
printf("input.txt Not found !\n Press any key to exit ");
getch();
return;
}
c=yylex();
while(c!=NULL)
{
yyout=fopen("C:\\ProCompFlex\\GnuWin32\\bin\\token.txt","w");
fprintf(yyout,c," ",yylex(),"\n");
getchar();
}
fclose(yyout);
}

Answer 1

您需要将所有关键字规则放在IDENTIFIER规则之前。