Re: OpenBSD's strlcpy(3) and strlcat(3)

[Bakul Shah]

Any use of str{,n}cat makes me gag.  In the past I have used
a composable function that may be of interest.  Composable in
the sense that the result can be immediately used as an arg
to another call and it doesn't have the O(N^2) behavior of
strcat.  Such a function can be totally safe.  Something like:

        char* r;
        r = scpy(char* dst, char* const dst_end, const char* src)

where the following post-conditions hold:

        dst_end >= dst
        r == MIN(dst + strlen(src)), dst_end)
        r[0] == '\0'

That is, the returned ptr points in `dst' _just_ past the
copied data.  Note that `dst_end' points to the _last_ char
of `dst'.

Example:

        char* string[N];
            ...
        char str[STRSIZE];
        char* const strend = str + sizeof str - 1;
        char* t = str;

        for (int i = 0; i < N && t < strend; i++)
                t = scpy(t, strend, string[i]);

or
        scpy(scpy(str, strend, "this"), strend, " and that"));


Here is the implementation:

char*
scpy(char* d, char* const e, const char* s)
{
        while (*s && d < e)
                *d++ = *s++;
        *d = '\0';
        return d;
}

This is far too simple to merit a paper or a long name :-)
And I am sure a zillion others have come up with the same idea.

-- bakul


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