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| From | Ben Bacarisse <ben.usenet@bsb.me.uk> |
|---|---|
| Newsgroups | comp.lang.c |
| Subject | Re: How to copy a string safely and efficiently in C? |
| Date | 2016-09-02 14:24 +0100 |
| Organization | A noiseless patient Spider |
| Message-ID | <87k2eu4ep7.fsf@bsb.me.uk> (permalink) |
| References | <0b30b0cc-f7c5-4928-8acb-56bf2364797b@googlegroups.com> <nqbo71$ou7$1@dont-email.me> |
Richard Heathfield <rjh@cpax.org.uk> writes:
> On 02/09/16 02:50, will hunt wrote:
>> should I use strncpy or snprintf, and why?
<snip>
> If losing data is acceptable, you can do this:
>
> #include <string.h>
>
> /* Copy As Much Of String As Possible (camosap) */
> /* target: destination string */
> /* maxlen: amount of storage allocated for string, inc null */
> /* source: place from which to copy data */
> /* return: 1 if truncated, else 0 */
>
> int camosap(char *target, size_t maxlen, char *source)
> {
> int truncated = 0;
> size_t len = strlen(source);
> if(len >= maxlen)
> {
> /* if the strings are guaranteed not to overlap, you
> can use memcpy instead of memmove */
> memmove(target, source, len);
> target[len] = '\0';
> truncated = 1;
> }
> else
> {
> strcpy(target, source);
> }
> return truncated;
> }
Several things have gone wrong with that. You overrun the buffer by
using len rather than maxlen and you are careful to allow copying
between overlapping objects in once case and then use strcpy in the
other (strcpy is undefined when the source and destination overlap).
And the setting of the null was probably intended to be
target[maxlen - 1] = '\0';
I find using maxlen for a size (i.e. a string length plus the
terminating null) to be rather confusing, especially as you also have
len which is a string length (excluding the terminating null).
If I had to maintain house style, I think I'd rewrite it, with a const
added as well, like this:
int camosap(char *target, size_t target_size, const char *source)
{
int truncated = 0;
size_t len = strlen(source);
if (len >= target_size)
{
/* if the strings are guaranteed not to overlap, you
can use memcpy instead of memmove */
memmove(target, source, target_size - 1);
target[target_size - 1] = '\0';
truncated = 1;
}
else
{
memmove(target, source, len + 1);
}
return truncated;
}
But I'd probably actually write like this, swapping the sense of the
return value as well (I suspect you favour zero for success for Anna
Karenina reasons):
int camosap(char *target, size_t target_size, const char *source)
{
size_t source_size = strlen(source) + 1;
if (source_size > target_size) {
memmove(target, source, target_size - 1);
target[target_size - 1] = '\0';
return 0;
}
memmove(target, source, source_size);
return 1;
}
<snip>
--
Ben.
Back to comp.lang.c | Previous | Next — Previous in thread | Next in thread | Find similar | Unroll thread
How to copy a string safely and efficiently in C? will hunt <glovepm@gmail.com> - 2016-09-01 18:50 -0700
Re: How to copy a string safely and efficiently in C? John Gordon <gordon@panix.com> - 2016-09-02 01:58 +0000
Re: How to copy a string safely and efficiently in C? will hunt <glovepm@gmail.com> - 2016-09-01 19:40 -0700
Re: How to copy a string safely and efficiently in C? Geoff <geoff@invalid.invalid> - 2016-09-01 20:29 -0700
Re: How to copy a string safely and efficiently in C? James Kuyper <jameskuyper@verizon.net> - 2016-09-02 12:29 -0400
Re: How to copy a string safely and efficiently in C? asetofsymbols@gmail.com - 2016-09-12 13:09 -0700
Re: How to copy a string safely and efficiently in C? Keith Thompson <kst-u@mib.org> - 2016-09-12 15:30 -0700
Re: How to copy a string safely and efficiently in C? Keith Thompson <kst-u@mib.org> - 2016-09-01 23:08 -0700
Re: How to copy a string safely and efficiently in C? Malcolm McLean <malcolm.mclean5@btinternet.com> - 2016-09-04 23:59 -0700
Re: How to copy a string safely and efficiently in C? Joe Pfeiffer <pfeiffer@cs.nmsu.edu> - 2016-09-01 21:12 -0600
Re: How to copy a string safely and efficiently in C? <william@wilbur.25thandClement.com> - 2016-09-01 22:12 -0700
Re: How to copy a string safely and efficiently in C? Malcolm McLean <malcolm.mclean5@btinternet.com> - 2016-09-01 23:58 -0700
Re: How to copy a string safely and efficiently in C? Ben Bacarisse <ben.usenet@bsb.me.uk> - 2016-09-02 10:42 +0100
Re: How to copy a string safely and efficiently in C? Tim Rentsch <txr@alumni.caltech.edu> - 2016-09-04 22:23 -0700
Re: How to copy a string safely and efficiently in C? Keith Thompson <kst-u@mib.org> - 2016-09-04 23:20 -0700
Re: How to copy a string safely and efficiently in C? mark.bluemel@gmail.com - 2016-09-05 01:03 -0700
Re: How to copy a string safely and efficiently in C? Keith Thompson <kst-u@mib.org> - 2016-09-05 01:46 -0700
Re: How to copy a string safely and efficiently in C? Ben Bacarisse <ben.usenet@bsb.me.uk> - 2016-09-05 10:30 +0100
Re: How to copy a string safely and efficiently in C? Tim Rentsch <txr@alumni.caltech.edu> - 2016-09-10 11:25 -0700
Re: How to copy a string safely and efficiently in C? Tim Rentsch <txr@alumni.caltech.edu> - 2016-09-11 06:23 -0700
Re: How to copy a string safely and efficiently in C? supercat@casperkitty.com - 2016-09-11 15:41 -0700
Re: How to copy a string safely and efficiently in C? Tim Rentsch <txr@alumni.caltech.edu> - 2016-09-11 23:40 -0700
Re: How to copy a string safely and efficiently in C? Ian Collins <ian-news@hotmail.com> - 2016-09-12 21:04 +1200
Re: How to copy a string safely and efficiently in C? Melzzzzz <Melzzzzz@zzzzz.com> - 2016-09-12 09:21 +0000
Re: How to copy a string safely and efficiently in C? Ian Collins <ian-news@hotmail.com> - 2016-09-12 21:33 +1200
Re: How to copy a string safely and efficiently in C? Ben Bacarisse <ben.usenet@bsb.me.uk> - 2016-09-12 10:41 +0100
Re: How to copy a string safely and efficiently in C? Melzzzzz <Melzzzzz@zzzzz.com> - 2016-09-12 10:48 +0000
Re: How to copy a string safely and efficiently in C? Tim Rentsch <txr@alumni.caltech.edu> - 2016-09-12 07:04 -0700
Re: How to copy a string safely and efficiently in C? Richard Heathfield <rjh@cpax.org.uk> - 2016-09-02 12:36 +0100
Re: How to copy a string safely and efficiently in C? Ben Bacarisse <ben.usenet@bsb.me.uk> - 2016-09-02 14:24 +0100
Re: How to copy a string safely and efficiently in C? Richard Heathfield <rjh@cpax.org.uk> - 2016-09-02 14:51 +0100
Re: How to copy a string safely and efficiently in C? Tim Rentsch <txr@alumni.caltech.edu> - 2016-09-04 23:42 -0700
Re: How to copy a string safely and efficiently in C? Richard Heathfield <rjh@cpax.org.uk> - 2016-09-02 18:05 +0100
Re: How to copy a string safely and efficiently in C? Ike Naar <ike@iceland.freeshell.org> - 2016-09-02 19:48 +0000
Re: How to copy a string safely and efficiently in C? cross@spitfire.i.gajendra.net (Dan Cross) - 2016-09-13 01:45 +0000
Re: How to copy a string safely and efficiently in C? Ben Bacarisse <ben.usenet@bsb.me.uk> - 2016-09-13 11:06 +0100
Re: How to copy a string safely and efficiently in C? cross@spitfire.i.gajendra.net (Dan Cross) - 2016-09-13 14:09 +0000
Re: How to copy a string safely and efficiently in C? Ben Bacarisse <ben.usenet@bsb.me.uk> - 2016-09-13 15:30 +0100
Re: How to copy a string safely and efficiently in C? cross@spitfire.i.gajendra.net (Dan Cross) - 2016-09-13 14:52 +0000
Re: How to copy a string safely and efficiently in C? cross@spitfire.i.gajendra.net (Dan Cross) - 2016-09-13 14:54 +0000
Re: How to copy a string safely and efficiently in C? Ben Bacarisse <ben.usenet@bsb.me.uk> - 2016-09-13 17:18 +0100
Re: How to copy a string safely and efficiently in C? cross@spitfire.i.gajendra.net (Dan Cross) - 2016-09-13 18:15 +0000
Re: How to copy a string safely and efficiently in C? Tim Rentsch <txr@alumni.caltech.edu> - 2016-09-13 20:30 -0700
Re: How to copy a string safely and efficiently in C? cross@spitfire.i.gajendra.net (Dan Cross) - 2016-09-15 14:03 +0000
Re: How to copy a string safely and efficiently in C? Tim Rentsch <txr@alumni.caltech.edu> - 2016-09-15 12:32 -0700
Re: How to copy a string safely and efficiently in C? luser droog <luser.droog@gmail.com> - 2016-09-15 12:45 -0700
Re: How to copy a string safely and efficiently in C? supercat@casperkitty.com - 2016-09-15 13:00 -0700
Re: How to copy a string safely and efficiently in C? Joe Pfeiffer <pfeiffer@cs.nmsu.edu> - 2016-09-15 14:52 -0600
Re: How to copy a string safely and efficiently in C? Keith Thompson <kst-u@mib.org> - 2016-09-15 16:04 -0700
Re: How to copy a string safely and efficiently in C? Joe Pfeiffer <pfeiffer@cs.nmsu.edu> - 2016-09-15 15:52 -0600
Re: How to copy a string safely and efficiently in C? Keith Thompson <kst-u@mib.org> - 2016-09-15 17:07 -0700
Re: How to copy a string safely and efficiently in C? Keith Thompson <kst-u@mib.org> - 2016-09-15 15:53 -0700
Re: How to copy a string safely and efficiently in C? Richard Heathfield <rjh@cpax.org.uk> - 2016-09-15 22:17 +0100
Re: How to copy a string safely and efficiently in C? Keith Thompson <kst-u@mib.org> - 2016-09-15 17:01 -0700
Re: How to copy a string safely and efficiently in C? supercat@casperkitty.com - 2016-09-15 16:36 -0700
Re: How to copy a string safely and efficiently in C? Keith Thompson <kst-u@mib.org> - 2016-09-15 19:19 -0700
Re: How to copy a string safely and efficiently in C? supercat@casperkitty.com - 2016-09-15 21:39 -0700
Re: How to copy a string safely and efficiently in C? Tim Rentsch <txr@alumni.caltech.edu> - 2016-09-16 06:17 -0700
Re: How to copy a string safely and efficiently in C? Malcolm McLean <malcolm.mclean5@btinternet.com> - 2016-09-16 07:04 -0700
Re: How to copy a string safely and efficiently in C? supercat@casperkitty.com - 2016-09-16 09:11 -0700
Re: How to copy a string safely and efficiently in C? Tim Rentsch <txr@alumni.caltech.edu> - 2016-09-22 22:24 -0700
Re: How to copy a string safely and efficiently in C? cross@spitfire.i.gajendra.net (Dan Cross) - 2016-09-19 15:15 +0000
Re: How to copy a string safely and efficiently in C? Richard Damon <Richard@Damon-Family.org> - 2016-09-13 08:19 -0400
Re: How to copy a string safely and efficiently in C? cross@spitfire.i.gajendra.net (Dan Cross) - 2016-09-13 14:07 +0000
Re: How to copy a string safely and efficiently in C? supercat@casperkitty.com - 2016-09-13 07:57 -0700
Re: How to copy a string safely and efficiently in C? Ben Bacarisse <ben.usenet@bsb.me.uk> - 2016-09-13 17:33 +0100
Re: How to copy a string safely and efficiently in C? cross@spitfire.i.gajendra.net (Dan Cross) - 2016-09-13 18:13 +0000
Re: How to copy a string safely and efficiently in C? supercat@casperkitty.com - 2016-09-13 11:30 -0700
Re: How to copy a string safely and efficiently in C? cross@spitfire.i.gajendra.net (Dan Cross) - 2016-09-13 20:03 +0000
Re: How to copy a string safely and efficiently in C? supercat@casperkitty.com - 2016-09-13 13:38 -0700
Re: How to copy a string safely and efficiently in C? cross@spitfire.i.gajendra.net (Dan Cross) - 2016-09-13 21:39 +0000
Re: How to copy a string safely and efficiently in C? Ben Bacarisse <ben.usenet@bsb.me.uk> - 2016-09-13 23:26 +0100
Re: How to copy a string safely and efficiently in C? Tim Rentsch <txr@alumni.caltech.edu> - 2016-09-13 16:14 -0700
Re: How to copy a string safely and efficiently in C? BartC <bc@freeuk.com> - 2016-09-13 15:59 +0100
Re: How to copy a string safely and efficiently in C? Tim Rentsch <txr@alumni.caltech.edu> - 2016-09-13 16:07 -0700
Re: How to copy a string safely and efficiently in C? cross@spitfire.i.gajendra.net (Dan Cross) - 2016-09-14 00:24 +0000
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