[Borg3]

#define strncpyz(d,s,l) *(strncpy(d,s,l)+(l))=0

Of course this one is unsafe for macro expansion. But well, its C :)

[teo_zero]

I'd rather put the final nul at d+l-1 than at d+l, so that l can be the size of d, not "one more than the size of d":

  strncpyz(buf,src,sizeof buf);