How do I use fscanf from the beginning each time when I am in a for / while loop?

Question

How do I use fscanf from the beginning each time when I am in a for loop?

I want to do something like this:

 for(i=0; i<5; i++)
      while(fscanf(in, "%d", &number)
            .......

Basically, when I use fscanf the first time, it starts scanning from the beginning of the file. I want it to start working from the beginning each time a for loop has been completed, how can I do that?

Answer 1

Use rewind() to seek back to the beginning of the file:

for (i = 0; i < 5; i++) {
    rewind(in);
    while (fscanf(in, "%d", &number)
        .......

Note however that this solution only works if the stream is seekable. If it is bound to a regular file, either opened by fopen or from a shell redirection, it should be seekable, but if it is bound to a terminal, a pipe or some other character device, rewind() may fail. You cannot test this with rewind() , but here is an alternative:

if (fseek(in, 0L, SEEK_SET)) {
    fprintf(stderr, "cannot rewind inut stream\n");
    exit(1);
}

A more reliable approach would be to save the values read by fscanf() to avoid seeking.