Re: [Libclc-developers] new string functions: clc_str{n}{case}comm()

[<bo...@me...>]

Hallvard B Furuseth wrote:
>>I think you should post the nice functions as well. Never know if
>>someone needs them or suddenly finds a new way of doing things. :-)
> 
> 
> OK, here are the clc_str{n}{case}comm() functions.  Does anyone need
> them?  I don't:-)

I have had use for functions like this. If you want to implement 
strtod() you must support the text "infinity", which can be abbreviated 
to "inf" and should be treated case insensitive as well.
	n = clc_strcasecomm(s, "infinity");
would have been nice to have in such cases.

I have some questions about the design. Allow for stupid questions here, 
hard to grasp everything at first try.

1. Why do you return -1 if s1 is shorter than s2? IMO that means that 
the length of the common part == strlen(s1).

2. The implementation crashes if s2 is shorter than s1 and shorter than 
len, doesn't it?

3. Why have a len at all? If you just want to see if the first n 
characters are common, can't memcmp, strncasecmp or others be used instead?

4. Given 1) and 3), why not return size_t? What can go wrong? If either 
of the strings are "", then return 0. When a char differs, return count 
so far.



> 
> NAME
>     clc_strcomm, clc_strncomm, clc_strcasecomm, clc_strncasecomm
>     - find common prefix of strings
> 
> SYNOPSIS
>     #include <clc_string.h>
>     long clc_strcomm(const char *s1, const char *s2);
>     long clc_strncomm(const char *s1, const char *s2, long len);
>     long clc_strcasecomm(const char *s1, const char *s2);
>     long clc_strncasecomm(const char *s1, const char *s2, long len);
> 
> DESCRIPTION
>     These functions find the length of the common prefix of two strings.
> 
>     clc_strcomm() and clc_strncomm() do case-sensitive compare,
>     clc_strcasecomm() and clc_strncasecomm() case-insensitive.
> 
>     clc_strcomm() and clc_strcasecomm() compare until the terminating
>     null characters.  clc_strncomm() and clc_strncasecomm() also stop
>     after len characters compared equal.
> 
>     If the strings are longer than LONG_MAX, the behaviors of
>     clc_strncomm() and clc_strncasecomm() are undefined.
> 
> RETURN VALUES
>     The functions return the common length of the strings, or -1 if the
>     strings compare equal.
> 
> CAVEATS
>     Note that the functions treat the size as long, not size_t.
> 
> SEE ALSO
>     clc(3), strcmp(3), strncmp(3), clc_strcasecmp(3), clc_strncasecmp(3)
> 
> 
> Implementation choices:
> - I used long instead of size_t as a length parameter to emphasize that
>   a long length is returned.
> - I could have returned an error condition (-2?) from clc_str{case}cmp
>   if the strings were equal for more than LONG_MAX characters, but
>   didn't bother.  I can't imagine these functions being used on other
>   than fairly short strings.
> 
> Source code for clc_strncasecomm() follows.  The others are for the time
> being left as an exercise for the reader.
> 
> 
> /* $Id$ */
> /*
>  * Copyright(c) 2003 Hallvard B Furuseth <h.b...@us...>
>  */
> 
> #include <ctype.h>
> #include <clc_assert.h>
> #include <clc_string.h>
> 
> long
> clc_strncasecomm(const char *s1, const char *s2, long len)
> {
>     const char *start = s1;
> 
> 	clc_assert_arg(clc_strncasecomm, s1 != NULL && s2 != NULL);
> 
>     for (; --len >= 0; ++s1, ++s2) {
> 		if (tolower((unsigned char)*s1) != tolower((unsigned char)*s2))
> 			return s1 - start;
> 		if (*s1 == '\0')
> 			break;
>     }
> 	return -1;
> }
> 
[snip]

-- 
boa

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