EOF reading last line twice

Question

I am pretty new to C and have a very simple function for displaying file contents here. It works fine, except the last line of my file prints twice...I know that it has to do w/EOF but I can't figure out how to get the function to recognize EOF as the last line and not run once more. I know there are a billion places on the internet with similar issues, but lots were for C++ and since I am new I thought it would be best to just use my own code. Here is the code:

 {
    int count=0, fileEnd=0;

    FILE* rockPtr=fopen("rockact.txt", "r");

    printf("\n%8s%8s%8s%8s%8s\n", "BANDID", "NAME", "SIZE", "CREW", "TRANS");

    do
    {
        fileEnd=fscanf(rockPtr, "%d%s%d%d%s", &(tempBand.rockid), tempBand.bandname, &(tempBand.bandsize), &(tempBand.crewsize), tempBand.transport);
            if (fileEnd !=EOF); //checks EOF has not been reached
            {
                printf("\n%8d%8s%8d%8d%8s", tempBand.rockid, tempBand.bandname, tempBand.bandsize, tempBand.crewsize, tempBand.transport);
                count++;                
            }               
    }
    while (fileEnd !=EOF);

    fclose(rockPtr);
    printf("\n The total amount of rock acts on file is %d\n", count);
    }

score 4 · Accepted Answer · answered Oct 17 '13 at 18:16

Your if condition doesn't want the semi-colon:

  if (fileEnd !=EOF); // This semicolon is wrong!

The semicolon is a null statement and is the body of the if.

I'd rather see the whole loop cast as a while loop:

while (fscanf(rockPtr, "%d%s%d%d%s", &tempBand.rockid, tempBand.bandname,
              &tempBand.bandsize, &tempBand.crewsize, tempBand.transport)) == 5)
{
    printf("\n%8d%8s%8d%8d%8s", tempBand.rockid, tempBand.bandname,
           tempBand.bandsize, tempBand.crewsize, tempBand.transport);
    count++;                
}

If you want to worry about it, you can spot the difference between EOF, read error and format error after the loop. Note that the check is that all values were converted OK.

Iłya Bursov · Answer 2 · 2013-10-17T18:24:53.287

1

you have ; after if - remove it

also, check manual for fscanf

If a reading error happens or the end-of-file is reached while reading, the proper indicator is set (feof or ferror). And, if either happens before any data could be successfully read, EOF is returned.

This mean that you can read at least partial data from file, reach EOF or error, but fscanf will not return it.

You should use feof function to check whether end of file is reached

so your logic should be:

read from file
if anything is read - display it, here I mean you should compare returned number with count of arguments, not with EOF
check for feof

UPDATE: during opening/reading from file you should always check ferror, as EOF is not the only problem

edited Oct 17 '13 at 18:24

answered Oct 17 '13 at 18:17

Iłya Bursov

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2

I'm deeply suspicious of 'use `feof()`' suggestions because there are many more ways to abuse it than there are to use it correctly. – Jonathan Leffler Oct 17 '13 at 18:21
2

[`while( !feof( file ) )` is always wrong](http://stackoverflow.com/questions/5431941/while-feof-file-is-always-wrong) – Grijesh Chauhan Oct 17 '13 at 18:23
I agree that you should check for reading errors too, updating – Iłya Bursov Oct 17 '13 at 18:23

EOF reading last line twice

2 Answers2