Why Does My EOF Check Repeat the Last Line When Reading a Text File?

Duplicate Bug: EOF Repeats Last Line in Text File Read

The code in question aims to read integers from a text file line by line until reaching the end-of-file (EOF) indicator. However, the final iteration unexpectedly reads the last integer twice.

Root of the Issue:

The issue lies in the nature of file reading. When the input stream reaches the EOF mark, the ios::eofbit is raised. This bit indicates that the last read operation encountered the EOF, not that the stream is at the end of the file.

Detailed Analysis:

Consider the following event sequence:

1. Read the integer 10.
2. Read the integer 20.
3. Read the integer 30.
4. Encounter the EOF after reading 30.

In the last iteration, the integer 30 is still the current value in the input stream. When the EOF is encountered, the ios::eofbit is raised, but the value of x remains 30. The code proceeds to output the value of x (which is 30) and checks for EOF in the loop condition. Since EOF is now set, the program exits the loop.

Suggested Fix:

To address this bug, replace the loop condition with a more explicit check for EOF:

while (true) {
    int x;
    iFile >> x;
    if (iFile.eof()) break;
    cerr << x << endl;
}

By explicitly checking for EOF after each read operation, the code ensures that the last integer is not read and printed twice.

Additional Bug:

The original code also lacks error checking. If the input file is empty, the loop will never terminate because the eofbit will not be raised until the first read operation encounters the EOF. To prevent this, add appropriate error handling before attempting to read from the file.

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