Is std::isspace the opposite of std::isgraph in C++ (locale versions)

Question

Is std::isspace the opposite of std::isgraph in C++ (locale versions)? That is, is the following true?

char c = getCharFromSomewhere();
std::locale loc = getLocaleFromSomewhere();
std::isspace(c, loc) != std::isgraph(c, loc)

They seem to be true when I test, but I can't be certain this is true in all locales.