Under what circumstances is a file stream object’s ios::badbit bit set? What member function reports the state of this bit?

ios::badbit is a flag used in C++ input/output (I/O) streams to indicate a critical error in the stream operations. When ios::badbit is set, it means that there is an unrecoverable error, and the program should handle it accordingly or stop further operations on the stream.

There are several circumstances under which ios::badbit can be set, which include: 1. Failure in memory allocation: This occurs when there is insufficient memory for the stream to perform its operations. 2. Writing to a file that is not open for writing: An attempt to write data to a file, which is not opened in write mode (or not open at all), will set the ios::badbit flag. 3. Reading from a file that is not open for reading: Similarly, attempting to read data from a file, which is not opened in read mode (or not open at all), will also set the ios::badbit flag. 4. Loss of integrity of the stream: If the stream becomes corrupted, for example, due to a hardware error, it will set the ios::badbit flag. 5. Attempting to perform operations on a closed file stream: Trying to execute any operation on a closed file stream triggers the ios::badbit flag.

The member function that reports the state of ios::badbit is called 'rdstate()'. This function returns the current state of the stream, including various flags such as ios::failbit, ios::eofbit, and ios::badbit. You can test specifically for the ios::badbit flag by using the bitwise AND operator with the rdstate() function, like this: ```cpp if (file_stream.rdstate() & std::ios::badbit) { // Handle the badbit error here } ```