c++ how to assert that all std::shared_ptr in a vector are referring to something

one more way to do it:

assert(std::find(pFoos.begin(), pFoos.end(), nullptr) == pFoos.end());

Another slightly convoluted way to express it with standard functionality only:

assert(std::none_of(pFoos.begin(), pFoos.end(), std::logical_not<std::shared_ptr<Foo>>{}));

From C++14 onwards, you can use the generic specialization of std::logical_not:

assert(std::none_of(pFoos.begin(), pFoos.end(), std::logical_not<>{}));