您好我想弄清楚是否合法（通过C ++）标准来计算某个成员的偏移量（为了扭转它）。
class A
{
public:
int a, b, c, d;
};
template <typename ParentClass, typename T>
ParentClass const * offset_this_pointer(T const * member_ptr, T ParentClass::* offset)
{
ParentClass const * parent_p = nullptr;
// we are technically dereferencing a NULL pointer here,
// but we are not using the result, only taking the address of it
// This works and yields the desired result in MSVC 2010, gcc 4.9.2 and Solaris10 compilers.
T const * offset_p = &(parent_p->*offset);
return reinterpret_cast<ParentClass const *>((uintptr_t)member_ptr - (uintptr_t)(offset_p));
}
int main()
{
A a;
assert(&a == offset_this_pointer(&a.b, &A::b)); // passes
return 0;
}
将&(parent_p->*offset) parent_p作为nullptr来进行private static final String API_HOST = "api.yelp.com";
static String DEFAULT_LOCATION = "London";
private static final int SEARCH_LIMIT = 20;
private static final String SEARCH_PATH = "/v2/search";
private static final String BUSINESS_PATH = "/v2/business";
request =new OAuthRequest(Verb.GET, "https://" + API_HOST + SEARCH_PATH);
request.addOAuthParameter(OAuthConstants.TIMESTAMP, seconds.toString());
request.addHeader(OAuthConstants.TIMESTAMP, seconds.toString());
request.addQuerystringParameter("term", DEFAULT_TERM);
request.addQuerystringParameter("location", DEFAULT_LOCATION);
request.addQuerystringParameter("limit", String.valueOf(SEARCH_LIMIT));
是合法的C ++吗？