how these file operations work?

[kocika73]

I have a question about the following code. I would like to know how the marked places work, I mean what is happening there.
I have a file, called info.dat, with some lines written by another program. This following code displays the contents of the file, and separates each line with a vertical tab.

#include <stdio.h>
#include <stdlib.h>

#define MAX 100

FILE *fp;

int main()
{
   char data[MAX];
  
   if( (fp = fopen("info.dat", "r")) == NULL )
   {
      printf("This file does not exist!");
      exit(0);
   }
   else
   {
      printf("First N: Last N: GPA\n\n");
      fgets(data, MAX, fp); /* does it read the whole file??? */
      while( !(foef(fp)) )
      {
         printf("%s\v", data); /* prints one line, how? */
         fgets(data, MAX, fp); /* huh? */
      }		 
   
   fclose(fp);
    }
   
   return 0;
}

I would appreciate if someone could enlighten me how it works.
Thanks.

[Dave_Sinkula]

fgets

[kocika73]

So, it reads one line at a time? And if I have a multiline file, e.g
blah bla 5.3
blah bla 3.7
blah vla 2.6
I need to put it in a while loop to read till the end of file? Is that right?

[0rion]

fgets() terminates when it encounters a newline character, so if you wanted to go through the whole file you would do something like this:

while(fgets(data,MAX,fp) != NULL)
{
    /* Do whatever */
}

Why do we check for NULL? Because fgets() returns a NULL whenever it encounters EOF or encounters an error.