Checking the state of a stream
Use this collection of methods to test for (or signal) errors and other exceptional conditions of streams:
ios::operator void* () const Method
You can do a quick check on the state of the most recent operation on a stream by examining a pointer to the stream itself. The pointer is arbitrary except for its truth value; it is true if no failures have occurred (ios::fail is not true). For instance, you might ask for input on cin only if all prior output operations succeeded, as in the following example.
if (cout)
{
// Everything OK so far
cin >> new_value;
...
}
ios::operator ! () const Method
In case it is more convenient to check whether something has failed, the operator, !, returns true if ios::fail is true (an operation has failed). For example, you might issue an error message if input failed, as in the following example.
if (!cin)
{
// Oops
cerr << "Eh?\n";
}
iostate ios::rdstate ()const < ffb /FONT>Method
Return the state flags for this stream. The value is from the enumeration iostate. You can test for any combination of the following flags.
void ios::setstate (iostate state) Method
Set the state flag for this stream to state in addition to any state flags already set. Synonym (for upward compatibility): ios::set.
See ios::clear to set the stream state without regard to existing state flags. See ios::good, ios::eof, ios::fail, and ios::bad, to test the state.
int ios::good ()const Method
Test the state flags associated with this stream; true if no error indicators are set.
int ios::bad ()const Method
Test whether a stream is marked as unusable. (Whether ios::badbit is set.)
int ios::eof ()const Method
True if end of file was reached on this stream. (If ios::eofbit is set.)
int ios::fail ()const Method
Test for any kind of failure on this stream: either some operation failed, or the stream is marked as bad. (If either ios::failbit or ios::badbit is set.)
void ios::clear (iostate state) Method
Set the state indication for this stream to the argument state. You may call ios::clear with no argument, in which case the state is set to good (no errors pending).
See ios::good, ios::eof, ios::fail, and ios::bad, to test the state; see ios::set or ios::setstate for an alternative way of setting the state.