On Sunday, January 30, 2022 at 8:02:26 AM UTC-5, Meredith Montgomery wrote:
> Manfred <non...@add.invalid> writes:
>
> > On 1/28/2022 8:52 PM, Meredith Montgomery wrote:
> >> I don't really get
> >> --8<---------------cut here---------------start------------->8---
> >> int strncmp(const char *s1, const char *s2, size_t n);
> >> The strncmp() function shall compare not more than n bytes (bytes
> >> that
> >> follow a NUL character are not compared) from the array pointed to by
> >> s1 to the array pointed to by s2.
> [...]
> > The more common use for strncmp is to test if two strings have a
> > common prefix.
> >
> > A more peculiar use is in the example given by James Kuyper: you get
> > strings in some constrained buffer, and the terminating '\0' is
> > included only if there is enough space in the buffer; in this scenario
> > you may set the third argument as the size of the buffer so as to
> > ensure that you don't read beyond the buffer limits.
> This makes perfect sense. I'm finally at peace with strncmp() and the
> others of the family. Thank you!

As an example of something like that,
if you wanted to write strstr() in C, you could use strncmp().

char *strstr(const char *s1, const char *s2)
{ const int c = *s2++;

if (c != '\0') {
const size_t n = strlen(s2);

s1 = strchr(s1, c);
while (s1 != NULL && strncmp(s1 + 1, s2, n) != 0) {
s1 = strchr(s1 + 1, c);
}
}
return (char *)s1;
}