Why Does `ifstream::eof()` Behave Differently with `get()` and the Extraction Operator (`>>`)?

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Diving into ifstream's eof() Function

Understanding the behavior of ifstream's eof() function can be puzzling, as illustrated in the provided code snippet:

</p>
<h1>include <iostream></h1>
<h1>include <fstream></h1>
<p>int main() {</p>
<pre class="brush:php;toolbar:false">std::fstream inf( "ex.txt", std::ios::in );
while( !inf.eof() ) {
    std::cout << inf.get() << "\n";
}
inf.close();
inf.clear();
inf.open( "ex.txt", std::ios::in );
char c;
while( inf >> c ) {
    std::cout << c << "\n";
}
return 0;

}

Let's delve into the explanation provided:

When EOF Really Sets In

The eof() function detects when a read operation attempts to access data beyond the end of the file. This means that:

• If you have a file with the content "abc" and read 3 characters, eof() will be false.
• But if you try to read a 4th character, eof() will become true, indicating that the end of the file has been reached.

The reason for this behavior is to ensure compatibility with different devices, such as pipes and sockets, where the concept of file size may not be as straightforward as with a text file.

Unveiling the Magic of get() and >>

The two loops in the code snippet use different approaches to read the contents of the file:

• The first loop uses inf.get() to retrieve characters one at a time. When the end of the file is reached, get() returns -1.
• The second loop uses inf >> c, which combines a read attempt and assignment in one operation. This approach sets c to the value read from the file, but if the read fails (due to reaching the end of the file), it evaluates to false, terminating the loop.

This explains why the first loop reads an extra character and displays -1, while the second loop gives the correct output – it terminates the loop before attempting to read beyond the end of the file.

Avoiding the Perils of -1

To avoid relying on the magic number -1 to identify the end of the file, it is recommended to use std::char_traits::eof() or std::istream::traits_type::eof() instead.

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