strtol.c File Reference

#include <ctype.h>
#include <limits.h>
#include <stdlib.h>

Include dependency graph for strtol.c:

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Functions
long	strtol (char *nptr, char **endptr, int base) const

Function Documentation

strtol()

long strtol	(	char*	nptr,
		char**	endptr,
		int	base
	)		const

Definition at line 78 of file strtol.c.

{
    register const char* s = nptr;
    register unsigned long acc;
    register int c;
    register unsigned long cutoff;
    register int neg = 0, any, cutlim;

    // check base
    if(base < 0 || base > 36)
    {
        // errno = EINVAL

        if(endptr)
        {
            *endptr = (char*)(uintptr_t)nptr;
        }

        return 0;
    }

    /*
     * 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;
    }
    else if((base == 0 || base == 2) && c == '0' && (*s == 'b' || *s == 'B'))
    {
        c = s[1];
        s += 2;
        base = 2;
    }
    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 = (int)(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 *= (unsigned long)base;
            acc += (unsigned long)c;
        }
    }
    if(any < 0)
    {
        acc = neg ? (unsigned long)LONG_MIN : (unsigned long)LONG_MAX;
        //      errno = ERANGE;
    }
    else if(neg)
    {
        acc = -acc;
    }
    if(endptr != 0)
    {
        *endptr = (char*)(uintptr_t)(any ? s - 1 : nptr);
    }
    return (long)(acc);
}

References isalpha(), isdigit(), isspace(), isupper(), and LONG_MIN.