arrays - How to read a file line-by-line in C?

Question

I have a text file with up to 100 IP addresses, 1 per line. I need to read each address, as a string, into an array called "list". First, I'm assuming that "list" will need to be a two-dimensional char array. Each IP address is 11 characters in length, 12 if you include '', so I declared list as follows:

char list[100][12];

Next, I attempt to use fgets to read the stream:

  for (i = 0; i < 100; i++)  
  {  
      if (feof(stream))  
          break;  
          for (j = 0; j < 12; j++)  
          fgets(&list[i][j], 12, stream);  
      count++;  
  }

To check to see if the strings were read properly, I attempt to output them:

  for (i = 0; i < 5; i++)  
  {  
      for (j = 0; j < 11; j++)  
          printf("%c", list[i][j]);  
      printf("
");  
  }

After running the program, it's clear something is wrong. Being a beginner, I'm not sure what, but I'm guessing I'm reading the file wrong. There are no errors. It compiles, but prints a strange address on two lines.

Edit:

I replaced the fgets code with this:

for (i = 0; i < 100; i++)
  {
      if (feof(stream))
          break;
      fgets(list[i], 12, stream);
      count++;
  }

It now prints five strings, but they are "random" characters from memory.

Answer 1

First, reading:

      for (j = 0; j < 12; j++)  
      fgets(&list[i][j], 12, stream);  

You have a big problem right here. This is attempting to read a string into each successive character in your array.

All in all, I think you're making this a lot more complex than it needs to be. Think of your array as 100 strings, and fgets will work with a string at a time. That means reading can look something like this:

for (i=0; i<100 && fgets(list[i], 11, string); i++)
    ;

There is one other minor detail to deal with: fgets() normally retains the new-line at the end of each line. As such, you may need to leave room for 13 characters (11 for address, 1 for new-line, 1 for NUL terminator), or else you may want to read the data into a temporary buffer, and copy it to your list only after you've stripped off the new-line.

In your current code for printing the strings, you're working one character at a time, which can work, but is unnecessarily difficult. Several people have suggested using the %s printf conversion, which is fine in itself. To go with it, however, you have to simplify your indexing a bit. Printing the first six addresses would look something like this:

for (i=0; i<6; i++)
    printf("%s", list[i]);