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From: Tim Rentsch <tr.17687@z991.linuxsc.com>
Newsgroups: comp.lang.c
Subject: Re: string to size_t
Date: Mon, 19 Dec 2022 11:20:07 -0800
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Keith Thompson <Keith.S.Thompson+u@gmail.com> writes:

> O?uz <oguzismailuysal@gmail.com> writes:
>
>> I wrote the function below for converting a string to size_t without
>> manually calculating its value digit by digit.  It first converts the
>> string to intmax_t, and if the conversion fails due to a range error
>> and SIZE_MAX doesn't fit into an intmax_t, it tries again with
>> uintmax_t.  In both cases, if the result is less than zero it
>> fails.  And on success it populates *result with the result.
>>
>> It works on my machine and a couple others I tried, but I'm not sure
>> if it's good C, or a good idea at all.  What do you think about it?
>>
>> int
>> strtosize(const char *nptr, char **endptr, int base, size_t *result) {
>> 	intmax_t s;
>> 	uintmax_t u;
>>
>> 	errno = 0;
>> 	s = strtoimax(nptr, endptr, base);
>>
>> 	if (errno == 0 && s >= 0 && s <= SIZE_MAX) {
>> 		*result = s;
>> 		return 1;
>> 	}
>>
>> #if SIZE_MAX > INTMAX_MAX
>> 	if (errno == ERANGE && s == INTMAX_MAX) {
>> 		errno = 0;
>> 		u = strtoumax(nptr, endptr, base);
>>
>> 		if (errno == 0 && u <= SIZE_MAX) {
>> 			*result = u;
>> 			return 1;
>> 		}
>> 	}
>> #endif
>>
>> 	if (errno == 0)
>> 		errno = ERANGE;
>>
>> 	return 0;
>> }
>
> What is the point of trying strotoimax before using strotoumax?
> Just call strtotumax and convert the result to size_t.
>
> The checks are probably unnecessary.  As of the current C standard,
> SIZE_MAX cannot be bigger than UINT_MAX.  (C23 will allow for
> the possibility that SIZE_MAX > UINT_MAX, but implementations are
> unlikely to take advantage of that -- which means your checking
> code will at best be difficult to test.)

I think you mean UINTMAX_MAX rather than UINT_MAX.