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From: Keith Thompson <Keith.S.Thompson+u@gmail.com>
Newsgroups: comp.lang.c
Subject: Re: string to size_t
Date: Mon, 19 Dec 2022 09:59:54 -0800
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Oğuz <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.)

-- 
Keith Thompson (The_Other_Keith) Keith.S.Thompson+u@gmail.com
Working, but not speaking, for XCOM Labs
void Void(void) { Void(); } /* The recursive call of the void */