From: Junio C Hamano <gitster@pobox•com>
To: Jeremiah Mahler <jmmahler@gmail•com>
Cc: Jonathan Nieder <jrnieder@gmail•com>, git@vger•kernel.org
Subject: Re: [PATCH v2 1/3] add strnncmp() function
Date: Tue, 17 Jun 2014 10:55:18 -0700 [thread overview]
Message-ID: <xmqqd2e7mneh.fsf@gitster.dls.corp.google.com> (raw)
In-Reply-To: <50de63f47ded2337adcd8bce151190fb99b38d64.1402990051.git.jmmahler@gmail.com> (Jeremiah Mahler's message of "Tue, 17 Jun 2014 00:34:37 -0700")
Jeremiah Mahler <jmmahler@gmail•com> writes:
> Add a strnncmp() function which behaves like strncmp() except it takes
> the length of both strings instead of just one. It behaves the same as
> strncmp() up to the minimum common length between the strings. When the
> strings are identical up to this minimum common length, the length
> difference is returned.
>
> Signed-off-by: Jeremiah Mahler <jmmahler@gmail•com>
> ---
> strbuf.c | 9 +++++++++
> strbuf.h | 2 ++
> 2 files changed, 11 insertions(+)
>
> diff --git a/strbuf.c b/strbuf.c
> index ac62982..4eb7954 100644
> --- a/strbuf.c
> +++ b/strbuf.c
> @@ -600,3 +600,12 @@ char *xstrdup_tolower(const char *string)
> result[i] = '\0';
> return result;
> }
> +
> +int strnncmp(const char *a, int len_a, const char *b, int len_b)
> +{
> + int min_len = (len_a < len_b) ? len_a : len_b;
> + int cmp = strncmp(a, b, min_len);
> + if (cmp)
> + return cmp;
> + return (len_a - len_b);
> +}
I am not sure if the interface into this function conceptually makes
much sense. strncmp(entry, string, 14) was invented as the way to
see if a NUL terminated "string" matches with the contents in an
array of char "entry" that is up to 14 bytes long, and because the
"entry" was allowed to fill full 14-byte space without terminated
with a NUL, the maximum possible length is specified separately, but
a NUL termination in "entry", if exists, is still honored. Is there
any case where such a pair of "maximum N bytes but could be shorter"
strings are compared, especially with different N's defined per
string, in our codebase (or in other people's project for that
matter)?
Further, I do think that the interface into this function and its
implementation are inappropriate for implementing the name_compare()
function in tree-walk.c and unpack-trees.c. These functions are
designed to take counted strings; in a tuple <a, a_len> they take,
"a_len" is the only thing that determines the length of string "a".
There is no room for a NUL termination inside "a" come into play to
make "a" shorter than "a_len".
In other words, "Two NUL-terminated strings can be compared with
strcmp(a, b), but we use counted strings in many places in our
codebase, and compare_counted_strings(a, a_len, b, b_len) function
would help us, so let's add one and use it in name_compare()" may
make good sense, but if we were to do so, I do not think strncmp()
would be involved in its implementation.
next prev parent reply other threads:[~2014-06-17 17:55 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-06-17 7:34 [PATCH v2 0/3] add strnncmp() function Jeremiah Mahler
2014-06-17 7:34 ` [PATCH v2 1/3] " Jeremiah Mahler
2014-06-17 8:23 ` Torsten Bögershausen
2014-06-17 15:48 ` Jeremiah Mahler
2014-06-17 9:09 ` Erik Faye-Lund
2014-06-17 15:49 ` Jeremiah Mahler
2014-06-17 17:55 ` Junio C Hamano [this message]
2014-06-17 19:27 ` Jeremiah Mahler
2014-06-17 7:34 ` [PATCH v2 2/3] tree-walk: simplify via strnncmp() Jeremiah Mahler
2014-06-17 7:34 ` [PATCH v2 3/3] unpack-trees: " Jeremiah Mahler
2014-06-17 11:08 ` [PATCH v2 0/3] add strnncmp() function Torsten Bögershausen
2014-06-17 15:49 ` Jeremiah Mahler
2014-06-17 17:48 ` Jonathan Nieder
2014-06-17 19:09 ` Jeremiah Mahler
2014-06-18 10:33 ` Ondřej Bílka
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=xmqqd2e7mneh.fsf@gitster.dls.corp.google.com \
--to=gitster@pobox$(echo .)com \
--cc=git@vger$(echo .)kernel.org \
--cc=jmmahler@gmail$(echo .)com \
--cc=jrnieder@gmail$(echo .)com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox