Reading data from datafile in C with feof()

Asked Mar 28 '18 at 13:14

Active Mar 28 '18 at 13:14

Viewed 18 times

I have a following simple code:

f = fopen("tdat.dat","r");

for(int i=0;;i++)
{
    if(feof(f)) break;
    fscanf(f,"%lf%lf%lf%lf",&x,&y,&z,&t);
    printf("%lf\t%lf\t%lf\t%lf\n",x,y,z,t);
}

and my datafile tdat.dat is as follows:

1.2 0.8 2.1 30.0
1.5 2.3 4.5 15.0
0.3 1.6 1.5 21.0

When I run the program, the result is:

1.200000    0.800000    2.100000    30.000000
1.500000    2.300000    4.500000    15.000000
0.300000    1.600000    1.500000    21.000000
0.300000    1.600000    1.500000    21.000000

My question is: why is there an additional line in the result that is same as the previous line? (This problem also appears when I use "while()" loop instead of for() loop)

Also, how can I avoid this problem?

asked Mar 28 '18 at 13:14

Lê Dũng

You don't care about the end of file, you care when `fscanf` doesn't convert what you asked it to. Use that return value instead. `while(fscanf(f,"%lf%lf%lf%lf",&x,&y,&z,&t) == 4) { do stuff }` – Retired Ninja Mar 28 '18 at 13:16
Thank you so much. I got it. – Lê Dũng Mar 28 '18 at 13:24

Reading data from datafile in C with feof()

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