Question

Use Lex to produce a lexical analyzer. You have to include all tests, make files, etc.

Answer 1

/* Tokens. */( better make a file and include that file in program)

#define IDENTIFIER 258

#define NUMBER 259

#define SIZEOF 260

#define PTR_OP 261

#define GT_OP 262

#define LT_OP 263

#define GE_OP 264

#define LE_OP 265

#define NE_OP 266

#define EQ_OP 267

#define AND_OP 268

#define OR_OP 269

#define DOT_OP 270

#define TYPEDEF 271

#define INT 272

#define CHAR 273

#define VOID 274

#define STRUCT 275

#define IF 276

#define ELSE 277

#define WHILE 278

#define RETURN 279

Normally, in a compiler, the parser frequently signals and calls the lexer, to returns the next token to the parser.

int main(){

int tok;

int n;

n = 0;

while(1) {

tok = yylex();

if(tok == 0)

break;

printf("line:%2d token type:%3d token text:(%s)\n", yylineno, tok, yytext);

n++;

}

printf("Number of tokens matched is %d\n",n);

return 0;

}

Generate the lexer using flex:

flex lex1.l

The result is in a file with name lex.yy.c. Compile and link:

gcc -c lex.yy.c

gcc lex.yy.o -ll

Sample Input and Output File: Below is a sample input file

/* comment */

void main(){

int i;

i=0;

while(i<10)

i=i+1;

}

and the corresponding output file

line: 2 token type:275 token text:(void)

line: 2 token type:258 token text:(main)

line: 2 token type: 40 token text:(()

line: 2 token type: 41 token text:())

line: 2 token type:123 token text:({)

line: 3 token type:273 token text:(int)

line: 3 token type:258 token text:(i)

line: 3 token type: 59 token text:(;)

line: 4 token type:258 token text:(i)

line: 4 token type: 61 token text:(=)

line: 4 token type:259 token text:(0)

line: 4 token type: 59 token text:(;)

line: 5 token type:279 token text:(while)

line: 5 token type: 40 token text:(()

line: 5 token type:258 token text:(i)

line: 5 token type:264 token text:(<)

line: 5 token type:259 token text:(10)

line: 5 token type: 41 token text:())

line: 6 token type:258 token text:(i)

line: 6 token type: 61 token text:(=)

line: 6 token type:258 token text:(i)

line: 6 token type: 43 token text:(+)

line: 6 token type:259 token text:(1)

line: 6 token type: 59 token text:(;)

line: 7 token type:125 token text:(})

Number of tokens matched is 25