EOF and Errors - GNU Octave
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#### 14.2.18 End of File and Errors

Once a file has been opened its status can be acquired. As an example the `feof` functions determines if the end of the file has been reached. This can be very useful when reading small parts of a file at a time. The following example shows how to read one line at a time from a file until the end has been reached.

         filename = "myfile.txt";
         fid = fopen (filename, "r");
         while (! feof (fid) )
           text_line = fgetl (fid);
         endwhile
         fclose (fid);

Note that in some situations it is more efficient to read the entire contents of a file and then process it, than it is to read it line by line. This has the potential advantage of removing the loop in the above code.

— Built-in Function: feof (fid)

> Return 1 if an end-of-file condition has been encountered for a given file and 0 otherwise. Note that it will only return 1 if the end of the file has already been encountered, not if the next read operation will result in an end-of-file condition.

> See also: fread, fopen, fclose.

— Built-in Function: [err, msg] = ferror (fid, "clear")

> Return 1 if an error condition has been encountered for the file ID fid and 0 otherwise. Note that it will only return 1 if an error has already been encountered, not if the next operation will result in an error condition.

> The second argument is optional. If it is supplied, also clear the error condition.

— Built-in Function: fclear (fid)

> Clear the stream state for the specified file.

— Built-in Function: freport ()

> Print a list of which files have been opened, and whether they are open for reading, writing, or both. For example:

>               freport ()

>                    -|  number  mode  name
>                    -|
>                    -|       0     r  stdin
>                    -|       1     w  stdout
>                    -|       2     w  stderr
>                    -|       3     r  myfile