Two behaviors changed since C++11.
1. The behavior of std::basic_ios::operator bool changed.
operator void*() const; (1) (until C++11)
explicit operator bool() const; (2) (since C++11)
Note since C++11 operator bool() is declared as explicit; but for if ((ss >> f) == false), ss (i.e. the return value of (ss >> f)) needs to be implicit converted to bool (to be compared with false), which is not allowed.
2. The definition of NULL (the null pointer constant) changed.
Before C++11 operator void*() could be used and it's not explicit (before C++11 there's no such thing like explicit user-defined conversion), and before C++11 NULL (the null pointer constant) is defined as
an integral constant expression rvalue of integer type that evaluates to zero
(until C++11)
which means false could be used as a null pointer constant. So ss could be implicitly converted to void* and then compared with false (as the null pointer).
From C++11 NULL is defined as
an integer literal with value zero, or a prvalue of type std::nullptr_t
(since C++11)
while false is not again; it's not an integer literal.
So from these two changes, after C++11 if ((ss >> f) == false) won't work again.
On the other hand, if (!(ss >> f)) works fine because there's std::basic_ios::operator! (both before and after C++11) for it.
bool operator!() const;
Returns true if an error has occurred on the associated stream.
Specifically, returns true if badbit or failbit is set in rdstate().
