Is `eof()` in File Input a Good Practice, and Why Is It Controversial?

eof() Usage in File Input: A Controversial Practice

Question:

Despite its common use in file input programs, the eof() function has stirred controversy. While some programmers deem it acceptable, others strongly advise against its use. This question explores the reasons behind this divide.

Answer:

The eof() function serves a specific purpose: to identify attempts to read beyond the end of a file. However, it is a poor choice for testing whether additional input remains or whether a read operation succeeded, two more common scenarios.

Why It's Considered Bad Practice:

The main reason eof() is discouraged is its ambiguity. It only indicates whether an attempt to read past the file's end has occurred. It does not provide information about whether valid data was actually read or if there is more data to process.

Example of Improper Use:

Consider the following incorrect usage:

while (!cin.eof()) {
  cin >> foo;
}

This loop assumes that eof() can determine whether there is input left to read. However, if a read operation fails for any reason other than reaching the end of file (e.g., invalid format), the loop will continue indefinitely.

Correct Usage:

To properly test for the specific condition eof() represents, employ the following approach:

if (!(cin >> foo)) {
  if (cin.eof()) {
    cout << "Read failed due to EOF\n";
  } else {
    cout << "Read failed due to something other than EOF\n";
  }
}

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