Hi Serge,
I proposed a few months ago to replace strncpy(3) by strlcpy(3BSD)[1].
However, strlcpy(3BSD) is not in glibc, and anyway, it's not ideal:
strlcat(3BSD) has quadratic time complexity, since it needs to re-read
the whole string for each copy.
[1]: <https://github.com/shadow-maint/shadow/issues/468>
I designed a function (based on other earlier interfaces, including
strecopy() and strlcpy(3BSD); see
<https://software.codidact.com/posts/285946>) that provides a better
behavior than any other string copy functions, with linear time complexity.
I propose to use it here, implementing it inside shadow-utils.
It is defined as:
char *stpecpy(char *dst, char *restrict src, char *end)
{
char *p;
p = memccpy(dst, src, '\0', end + 1 - dst);
if (p != NULL)
return p - 1;
/* truncation detected */
*end = '\0';
return end + 1;
}
To be used as:
end = buf + sizeof(buf) - 1;
len = stpecpy(stpecpy(buf, "Hello", end), " world", end) - buf;
if (len == sizeof(buf)) {
len--;
handle_trunc();
}
So the 3 main alternatives to strncpy(3) are:
- strlcpy(3BSD) + strlcat(3BSD)
BSD
good interface
bad performance
- memccpy(3)
ISO C
good performance
bad interface
- stpecpy()
custom
good performance
good interface
What are your thoughts?
Regards,
Alex
--
Alejandro Colomar
Linux man-pages comaintainer; http://www.kernel.org/doc/man-pages/
http://www.alejandro-colomar.es/
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