Category : C Source Code
Archive   : SNIP1292.ZIP
Filename : SCANFRAC.C

/* function scanfrac - scan an input string for a numeric value.
**
** Written in ANSI C and contributed to the public domain by
** Thad Smith III, Boulder, CO. August 5, 1991
*/

/*******************************************************************
** scanfrac() scans an input string for a numeric value, which can
** be specified as:
** 1. an integer, 5
** 2. a floating point value, 5.1
** 3. a fraction, or 3/4
** 4. a mixed fraction. 5 3/4 or 5-3/4
**
** Conditions:
** 1. Preceeding whitespace is allowed.
** 2. The input number may be signed.
** 3. The fractional part of a mixed fraction (but not pure fraction)
** must be less than 1.
** 4. The numerator and denominator of a fraction or mixed fraction
** must be less than 2^31.
**
** Parameters:
** 1. Input buffer containing value.
** 2. Pointer to double to receive return value.
**
** Return status:
** 0 = OK, value returned in f,
** 1 = bad input format,
** 2 = can't allocate memory
*/

#include
#include
#include
#include

int scanfrac (const char buf[], double *f)
{
char *tbuf = malloc (strlen(buf) +2); /* input + terminator */
static char term[] = "\a"; /* terminator flag */
char t1,t2,t3; /* separator chars */
char sign; /* possible sign */
int nc; /* # conversions */
long int b,c; /* 2nd & 3rd inputs */

if (!tbuf) /* couldn't allocate memory */
return 2;

/* Copy the input to a temporary buffer and append a terminator
** character. This terminator is used to determine whether the
** scanning of the input field by sscanf() was terminated by end
** of input or by an invalid character. If terminated properly,
** the terminator character picked up in t1, t2, or t3.
*/

strcat (strcpy(tbuf, buf), term); /* input + term flag */
nc = sscanf (tbuf, " %lf%c %ld %c %ld %c",
f,&t1,&b,&t2,&c,&t3);
free (tbuf);

switch (nc) /* number of sscanf() conversions */
{
case 2: /* single floating value: a */
if (t1 == *term) return 0;
break;
case 4: /* pure fraction: a/b */
if (t1 == '/' && t2 == *term && fmod (*f,1.0) == 0.0 && b > 0)
{
*f /= b;
return 0;
}
break;
case 6: /* mixed fraction: a b/c or a-b/c */
if ((t1 == ' ' || t1 == '-') && t2 == '/' && t3 == *term &&
fmod (*f,1.0) == 0.0 && b >= 0 && c > b)
{
/* get first non-blank character so that
** -0 b/c will be neg
*/

#ifdef __ZTC__ /* fix for missing const in sscanf() declaration */
sscanf ((char*)buf, " %c", &sign);
#else
sscanf (buf, " %c", &sign);
#endif
if (sign == '-')
*f -= (double)b/c;
else *f += (double)b/c;
return 0;
}
}
return 1;
}

/* This is a simple test driver. It should be omitted before
** placing scanfrac() into a library.
*/

main ()
{
char buf[80];
double f;
int stat;

printf ("Enter 999. or generate EOF to stop\n");
do
{
printf ("Enter value: ");
if (! gets (buf))
{
printf ("EOF detected. Aborting.\n");
return 1;
}
stat = scanfrac (buf, &f);
printf ("\nStat = %d, value = %f\n", stat, f);
} while ( f != 999.);
return 0;
}