namespace std {
template<class charT, class traits = char_traits<charT>>
class basic_ostream<charT, traits>::sentry {
bool ok_;
public:
explicit sentry(basic_ostream<charT, traits>& os);
~sentry();
explicit operator bool() const { return ok_; }
sentry(const sentry&) = delete;
sentry& operator=(const sentry&) = delete;
};
}
The class
sentry
defines a class that is responsible for doing exception safe prefix and suffix
operations
.explicit sentry(basic_ostream<charT, traits>& os);
If
os.good()
is nonzero, prepares for formatted or unformatted output
.If
os.tie()
is not a null pointer, calls
os.tie()->flush().If, after any preparation is completed,
os.good()
is
true,
ok_ == true
otherwise,
ok_ == false.During preparation, the constructor may call
setstate(failbit)
(which may throw
ios_base::failure (
[iostate.flags]))
.If
(os.flags() & ios_base::unitbuf) && !uncaught_exceptions()
&& os.good()
is
true,
calls
os.rdbuf()->pubsync().If that function returns -1, sets
badbit in
os.rdstate() without propagating an exception
.explicit operator bool() const;