Help needed with strtod

[broli86]

As you can see the first double value in the string i.e. 123.4444e-309 should cause underflow yet i am getting 0.000000 33.4444 -10.555 as the output. The too_small remains 0 . Have I made a mistake in my logic ?

 #include <stdio.h>
 #include <stdlib.h>
 #include <errno.h>
 #include <math.h>

 int main(void)
 {
	char s[] = "123.4444e-309 33.4444 -10.555";
	char *endptr1, *endptr2, *endptr3;
	double f1, f2, f3;
	int too_big = 0;
	int too_small = 0;

	errno = 0;
	f1 = strtod(s, &endptr1);
	too_big |= fabs(f1) == HUGE_VAL && errno == ERANGE;
	too_small |= f1 == 0.0 && errno == ERANGE;

	errno = 0;
	f2 = strtod(endptr1, &endptr2);
	too_big |= fabs(f2) == HUGE_VAL && errno == ERANGE;
	too_small |= f2 == 0.0 && errno == ERANGE;

	errno = 0;
	f3 = strtod(endptr2, &endptr3);
	too_big |= fabs(f3) == HUGE_VAL && errno == ERANGE;
	too_small |= f3 == 0.0 && errno == ERANGE;

	if (too_big)
	{
		fprintf(stderr,"Overflow error\n");
		return (1);
	}
	else
	{
		if (too_small)
		{
			fprintf(stderr, "Underflow error\n");
			return (1);
		}
		else
		{
			if (s == endptr1 || endptr1 == endptr2 || endptr2 == endptr3)
			{
				fprintf(stderr, "Conversion failed\n");
				return (1);
			}
		}
	}

	printf(" &#37;f %f %f\n", f1, f2, f3);
	return (0);
}

[Elysia]

You only need to check for ERANGE if there's underflow or overflow, nothing else.
It's probably why you get false results.

[broli86]

You only need to check for ERANGE if there's underflow or overflow, nothing else.
It's probably why you get false results.

Ok I changed my code , please have a look :

 int main(void)
 {
        char s[50], *ptr = NULL;
	char *endptr1, *endptr2, *endptr3;
	double f1, f2, f3;
	int too_big = 0;

        if (fgets(s, 50, stdin) == NULL)
        {
                fprintf(stderr, "ERROR IN INPUT STRING\n");
                return (1);
        }
        if ((ptr = strchr(s, '\n')) != NULL)
        {
                *ptr = '\0';
        }

	errno = 0;
	f1 = strtod(s, &endptr1);
        too_big |= errno == ERANGE;
     

	errno = 0;
	f2 = strtod(endptr1, &endptr2);
        too_big |= errno == ERANGE;
   

	errno = 0;
	f3 = strtod(endptr2, &endptr3);
        too_big |= errno = ERANGE;

	if (too_big)
	{
                fprintf(stderr,"OUT OF RANGE OF REPRESENTABLE VALUES\n");
		return (1);
	}
        else
        {
                if (s == endptr1 || endptr1 == endptr2 || endptr2 == endptr3)
                {
                                fprintf(stderr, "CONVERSION OF STRING FAILED\n");
				return (1);
                }
                
	}

	printf(" %f %f %f\n", f1, f2, f3);
	return (0);
}

With this even if I type some illegible string like "24-asd;f'jf 35905ye 3ssfa" it gives me OUT OF RANGE OF REPRESENTABLE VALUES. Why not "Conversion of string failed " ? Is it still flawed ?

[Elysia]

too_big |= errno == ERANGE;
Can be just (or should be)
too_big = (errno == ERANGE);

With this even if I type some illegible string like "24-asd;f'jf 35905ye 3ssfa" it gives me OUT OF RANGE OF REPRESENTABLE VALUES. Why not "Conversion of string failed " ? Is it still flawed ?

Yes. Use the endptrX argument you're defined to check if the conversion is invalid.
If the entire expression wasn't parsed, it probably means an invalid number.

[broli86]

too_big |= errno == ERANGE;
Can be just (or should be)
too_big = (errno == ERANGE);


Yes. Use the endptrX argument you're defined to check if the conversion is invalid.
If the entire expression wasn't parsed, it probably means an invalid number.

The endptr pointer (if not passed as NULL) will point to the start of the input string if no conversion was done. If any characters were used, it will be advanced. That's why I checked for :

  if (s == endptr1 || endptr1 == endptr2 || endptr2 == endptr3)

[Elysia]

But the string was partially parsed, so check for the end of the string.

[broli86]

#include <stdio.h>
#include <stdlib.h>
#include <errno.h>
#include <math.h>
#include <string.h>

int string_to_double(char *s, char **endptr, double *f)
{
        int too_big = 0;

        errno = 0;

        *f = strtod(s, endptr);
        too_big = (errno == ERANGE);

        if (too_big)
        {
                fprintf(stderr, "OUT OF RANGE OF REPRESENTABLE VALUES\n");
                return (1);
        }
        else
        {
                if (s == *endptr)
                {
                        fprintf(stderr, "CONVERSION OF STRING FAILED\n");
                        return (1);
                }
        }

        return (0);
}


int main(void)
{
       char s[50], *ptr = NULL;
       char *endptr1, *endptr2, *endptr3;
       double f1, f2, f3;
	 int rc;

       if (fgets(s, 50, stdin) == NULL)
       {
               fprintf(stderr, "ERROR IN INPUT STRING\n");
               return (1);
       }
       if ((ptr = strchr(s, '\n')) != NULL)
       {
               *ptr = '\0';
       }

       rc = (string_to_double(s, &endptr1, &f1) == 0) &&       
            (string_to_double(endptr1, &endptr2, &f2) == 0) &&
            (string_to_double(endptr2, &endptr3, &f3) == 0);


       if (rc == 1)
       {
	 	  printf("&#37;f %f %f\n", f1, f2, f3);
       }
                              
       return (!rc);
}

This seems to work.