Re: The difference between strtol() and strtoul() ?

On Fri, 21 Jun 2024 14:38:56 -0400
James Kuyper <jameskuyper@alumni.caltech.edu> wrote:

On 6/21/24 11:53, Michael S wrote:

On Fri, 21 Jun 2024 18:28:39 +0300
Michael S <already5chosen@yahoo.com> wrote:
 

On Fri, 21 Jun 2024 13:58:01 -0000 (UTC)
gazelle@shell.xmission.com (Kenny McCormack) wrote: 

>
Yeah, now I get it.  You really only need strtoimax() and
strtoumax().  

>
Which are? uunfortunately, not part of C standard. 

 
They have been part of the C standard since C99.
 

BTW, I don't know what The Standard says about out-of-range inputs,
but at least https://en.cppreference.com/w/c/string/byte/strtol
does not say anything certain. especially about what stored in
*str_end. 

 
"The strtoimax and strtoumax functions are equivalent to the strtol,
strtoll, strtoul, and strtoull functions, except that the initial
portion of the string is converted to intmax_t and uintmax_t
representation, respectively." (7.8.2.3p2)
 
You need to go to the descriptions of those other functions to get the
detailed specifications.
 
"If the correct value is outside the range of representable values,
LONG_MIN, LONG_MAX, LLONG_MIN, LLONG_MAX, ULONG_MAX, or ULLONG_MAX is
returned (according to the return type and sign of the value, if any),
and the value of the macro ERANGE is stored in errno."
 
As I understand it, that means that if the input string represents a
value outside of the range of representable values, then strtoimax()
should return INTMAX_MIN or INTMAX_MAX, depending upon the sign, and
strtouimax() should return UINTMAX_MAX. Both of them should store the
value of ERANGE in errno, to distinguish these results from what you
would get if the string happened to represent those values.
 

That what is done by my implementation, but I can not understand how it
follows from the text, esp. for a case of out of range negative input
for strtou**() functions.
That creates rather non-intuitive discontinuity.
  strtoull("-18446744073709551615") => 1
  strtoull("-18446744073709551616") => 18446744073709551615

 
The C standard uses end_ptr rather than str_end in it's description of
these functions.
 
"... First, they decompose the input string into three parts: an
initial, possibly empty, sequence of white-space characters, a subject
sequence resembling an integer represented in some radix determined by
the value of base, and a final string of one or more unrecognized
characters, including the terminating null character of the input
string. ..." (7.21.4.7p2).
 
That defines what the "final string" is.
 
"If the subject sequence has the expected form, ... A pointer to the
final string is stored in the object pointed to by endptr, provided
that endptr is not a null pointer." (7.24.1.7p5).
 
"If the subject sequence is empty or does not have the expected form
... the value of nptr is stored in the object pointed to by endptr,
provided that endptr is not a null pointer." (7.21.4.7p7)
 
That seems very precise and unambiguous to me, aside from what "the
expected form" is, which is described elsewhere.

Yes, this part of description is good and unambiguous. 
I wonder why cppreference.com had chosen to use less clear wording "The
functions set the pointer pointed to by str_end to point to the
character past the last numeric character interpreted."