Understand the subtleties of feof

The return value of this function is written in msdn as follows:FeofFunction returns a nonzero value after the first read operation that attempts to read past the end of the file. It returns 0 if the current position is not end of file.

For example, if I use the fgets function to read a file and read the byte at the end of the file, then fgets returns NULL. Then, you can use feof to determine whether the file has ended or whether a read error has occurred.

Here is a subtle point to note. If you read all this file, the file pointer is already at the end of the file, but you can use the feof function to determine whether the file is over, this function returns NULL. The non-zero value is returned only when the feof function is called after the read operation is performed again.