and *((char*)mempcpy(dst, src, min(len, dstsize-1))) = 0; can be replace by ((char*)memcpy(dst, src, min(len, dstsize-1))[min(len, dstsize-1)] = 0;

and *((char*)mempcpy(dst, src, min(len, dstsize-1))) = 0; can be replace by ((char*)memcpy(dst, src, min(len, dstsize-1))[min(len, dstsize-1)] = 0; if you don't have mempcpy