error during the compilation_undefined reference - gcc

Question

my file myComp.l
%{
#include <stdlib.h>
#include <stdio.h>
#include "y.tab.h"
int yyerror(char *);
%}
%%
[a-z] {
yylval = *yytext - 'a';
return VAR;
}
[0-9]+ {
yylval = atoi(yytext);
return INT;
}
[-+()=/*\n] { return *yytext; } [ \t] ;
. { yyerror("Input non valido"); }
%% int yywrap(void){
return 1; }
and this is the file myComp.y
%{ /* Prologo */
#define YYSTYPE int
#include <math.h>
#include <stdio.h>
int yyerror(char *);
int yylex(void) ;
int sym[26];
%}
/* Definizioni */
%token INT VAR
%left '+' '-'
%left '*' '/'
%%
program:
program statement '\n'
|
;
statement:
expr { printf("%d\n", $1); }
| VAR '=' expr { sym[$1] = $3; }
;
expr:
INT
| VAR { $$ = sym[$1]; }
| expr '+' expr { $$ = $1 + $3; }
| expr '-' expr { $$ = $1 - $3; }
| expr '*' expr { $$ = $1 * $3; }
| expr '/' expr { $$ = $1 / $3; }
| '(' expr ')' { $$ = $2; }
;
%%
int yyerror(char *s) {
fprintf(stderr, "%s\n", s);
return 1;
}
int main( void ) {
yyparse();
return 0;
}
i used this commands for compiling
flex myComp.l
bison -y myComp.y
gcc -o myComp y.tab.c
but i have this error:
/tmp/ccaHRWZu.o: In function `yyparse':
y.tab.c:(.text+0x24a): undefined reference to `yylex'
collect2: ld returned 1 exit status
all programs that i installed are updated in the last version.i can't unterstand where is the problem?what i can i do for risolving this error.please help me to fix it.thanks all
thk's all

Answer 1

you are missing the linker flag -lfl to link your parser against the flex library where yylex is defined. Additionally you need to build the output of flex, too. That c-file is probably called: myComp.lex.c
compile with:
gcc -o myComp y.tab.c myComp.lex.c -lfl