strtol.c

标准c库代码,可以应用于各个系统提供了大量的基本函数

/*
FUNCTION
   <<strtol>>---string to long

INDEX
	strtol
INDEX
	_strtol_r

ANSI_SYNOPSIS
	#include <stdlib.h>
        long strtol(const char *<[s]>, char **<[ptr]>,int <[base]>);

        long _strtol_r(void *<[reent]>, 
                       const char *<[s]>, char **<[ptr]>,int <[base]>);

TRAD_SYNOPSIS
	#include <stdlib.h>
	long strtol (<[s]>, <[ptr]>, <[base]>)
        char *<[s]>;
        char **<[ptr]>;
        int <[base]>;

	long _strtol_r (<[reent]>, <[s]>, <[ptr]>, <[base]>)
	char *<[reent]>;
        char *<[s]>;
        char **<[ptr]>;
        int <[base]>;

DESCRIPTION
The function <<strtol>> converts the string <<*<[s]>>> to
a <<long>>. First, it breaks down the string into three parts:
leading whitespace, which is ignored; a subject string consisting
of characters resembling an integer in the radix specified by <[base]>;
and a trailing portion consisting of zero or more unparseable characters,
and always including the terminating null character. Then, it attempts
to convert the subject string into a <<long>> and returns the
result.

If the value of <[base]> is 0, the subject string is expected to look
like a normal C integer constant: an optional sign, a possible `<<0x>>'
indicating a hexadecimal base, and a number. If <[base]> is between
2 and 36, the expected form of the subject is a sequence of letters
and digits representing an integer in the radix specified by <[base]>,
with an optional plus or minus sign. The letters <<a>>--<<z>> (or,
equivalently, <<A>>--<<Z>>) are used to signify values from 10 to 35;
only letters whose ascribed values are less than <[base]> are
permitted. If <[base]> is 16, a leading <<0x>> is permitted.

The subject sequence is the longest initial sequence of the input
string that has the expected form, starting with the first
non-whitespace character.  If the string is empty or consists entirely
of whitespace, or if the first non-whitespace character is not a
permissible letter or digit, the subject string is empty.

If the subject string is acceptable, and the value of <[base]> is zero,
<<strtol>> attempts to determine the radix from the input string. A
string with a leading <<0x>> is treated as a hexadecimal value; a string with
a leading 0 and no <<x>> is treated as octal; all other strings are
treated as decimal. If <[base]> is between 2 and 36, it is used as the
conversion radix, as described above. If the subject string begins with
a minus sign, the value is negated. Finally, a pointer to the first
character past the converted subject string is stored in <[ptr]>, if
<[ptr]> is not <<NULL>>.

If the subject string is empty (or not in acceptable form), no conversion
is performed and the value of <[s]> is stored in <[ptr]> (if <[ptr]> is
not <<NULL>>).

The alternate function <<_strtol_r>> is a reentrant version.  The
extra argument <[reent]> is a pointer to a reentrancy structure.

RETURNS
<<strtol>> returns the converted value, if any. If no conversion was
made, 0 is returned.

<<strtol>> returns <<LONG_MAX>> or <<LONG_MIN>> if the magnitude of
the converted value is too large, and sets <<errno>> to <<ERANGE>>.

PORTABILITY
<<strtol>> is ANSI.

No supporting OS subroutines are required.
*/

/*
 * Andy Wilson, 2-Oct-89.
 */

#include <_ansi.h>
#include "std.h"

long
_DEFUN (_strtol_r, (rptr, s, ptr, base),
	struct _reent *rptr _AND
	_CONST char *s _AND
	char **ptr _AND
	int base)
{
  int minus = 0;
  unsigned long tmp;
  _CONST char *start = s;
  char *eptr;

  if (s == NULL)
    {
      rptr->_errno = ERANGE;
      if (!ptr)
	*ptr = (char *) start;
      return 0L;
    }
  while (Isspace (*s))
    s++;
  if (*s == '-')
    {
      s++;
      minus = 1;
    }
  else if (*s == '+')
    s++;

  /*
   * Let _strtoul_r do the hard work.
   */

  tmp = _strtoul_r (rptr, s, &eptr, base);
  if (ptr != NULL)
    *ptr = (char *) ((eptr == s) ? start : eptr);
  if (tmp > (minus ? - (unsigned long) LONG_MIN : (unsigned long) LONG_MAX))
    {
      rptr->_errno = ERANGE;
      return (minus ? LONG_MIN : LONG_MAX);
    }
  return (minus ? (long) -tmp : (long) tmp);
}

#ifndef _REENT_ONLY

long
_DEFUN (strtol, (s, ptr, base),
	_CONST char *s _AND
	char **ptr _AND
	int base)
{
  return _strtol_r (_REENT, s, ptr, base);
}

#endif