Checking Error State

To be MT-safe, error checking must occur in a critical region with the I/O operation that causes the error. The following example illustrates how to check for errors:

Example 11–1 Checking Error State

#include <iostream.h>
enum iostate {IOok, IOeof, IOfail};

iostate read_number(istream& istr, int& num)
{
    stream_locker sl(istr, stream_locker::lock_now);

    istr >> num;

    if (istr.eof()) return IOeof;
    if (istr.fail()) return IOfail;
    return IOok;
}

In this example, the constructor of the stream_locker object sl locks the istream object istr. The destructor of sl, called at the termination of read_number, unlocks istr.