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/*
Article 4291 of comp.lang.c:
From: chris@mimsy.umd.edu (Chris Torek)
Newsgroups: comp.lang.c
Subject: Re: error checking strtol
Message-ID: <24445@mimsy.umd.edu>
Date: 17 May 90 09:31:17 GMT
Organization: U of Maryland, Dept. of Computer Science, Coll. Pk., MD 20742
The following is a working strtol. It depends only on the existence of
correct header files (including <limits.h>) and on ASCII (IBM programmers
will have to use strchr()). It does not support locales other than `C'.
System V programmers should be able to replace their current strtol with
this one. (After writing this, I checked the SVR2 source; it did not
handle several cases correctly.)
*/
#ifdef __STDC__
#include <limits.h>
#else
#define LONG_MIN (-0x80000000) /* for 32-bit 2s-complement at least */
#define LONG_MAX 0x7fffffff
#endif
#if 0
#include <limits.h>
#include <ctype.h>
#include <errno.h>
#endif
#ifndef _MSC_VER
int errno;
#endif
/*
* Convert a string to a long integer.
*
* Ignores `locale' stuff. Assumes that the upper and lower case
* alphabets and digits are each contiguous.
*/
long
strtol(nptr, endptr, base)
const char *nptr;
char **endptr;
register int base;
{
register const char *s = nptr;
register unsigned long acc;
register int c;
register unsigned long cutoff;
register int neg = 0, any, cutlim;
/*
* Skip white space and pick up leading +/- sign if any.
* If base is 0, allow 0x for hex and 0 for octal, else
* assume decimal; if base is already 16, allow 0x.
*/
do {
c = *s++;
} while (isspace(c));
if (c == '-') {
neg = 1;
c = *s++;
} else if (c == '+')
c = *s++;
if ((base == 0 || base == 16) &&
c == '0' && (*s == 'x' || *s == 'X')) {
c = s[1];
s += 2;
base = 16;
}
if (base == 0)
base = c == '0' ? 8 : 10;
/*
* Compute the cutoff value between legal numbers and illegal
* numbers. That is the largest legal value, divided by the
* base. An input number that is greater than this value, if
* followed by a legal input character, is too big. One that
* is equal to this value may be valid or not; the limit
* between valid and invalid numbers is then based on the last
* digit. For instance, if the range for longs is
* [-2147483648..2147483647] and the input base is 10,
* cutoff will be set to 214748364 and cutlim to either
* 7 (neg==0) or 8 (neg==1), meaning that if we have accumulated
* a value > 214748364, or equal but the next digit is > 7 (or 8),
* the number is too big, and we will return a range error.
*
* Set any if any `digits' consumed; make it negative to indicate
* overflow.
*/
cutoff = neg ? -(unsigned long)LONG_MIN : LONG_MAX;
cutlim = cutoff % (unsigned long)base;
cutoff /= (unsigned long)base;
for (acc = 0, any = 0;; c = *s++) {
if (isdigit(c))
c -= '0';
else if (isalpha(c))
c -= isupper(c) ? 'A' - 10 : 'a' - 10;
else
break;
if (c >= base)
break;
if (any < 0 || acc > cutoff || acc == cutoff && c > cutlim)
any = -1;
else {
any = 1;
acc *= base;
acc += c;
}
}
if (any < 0) {
acc = neg ? LONG_MIN : LONG_MAX;
errno = ERANGE;
} else if (neg)
acc = -acc;
if (endptr != 0)
*endptr = (char *) (any ? s - 1 : nptr);
return (acc);
}
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