如何在文本文件中写空行？

Question

I'm writing a program to keep an inventory of books, it reads a list of books from a text file and also writes additional books into the file. I got it to add new books to the file, but I would like to have a blank line between each book entry. How can I do that? Some other info that might be useful or needed: I'm using a structure to hold the title, author, and ISBN all in character strings.

Here's the part that collects the new data: It's put into a linked list.

puts("Enter first book title.");
while(fgets(input, 80, stdin) != NULL && input[0] != '\n')
{
current = (struct book *)malloc(sizeof(struct book));
if(head == NULL)
   head = current;
else
   prev->next = current;
current->next = NULL;

strcpy(current->title, input);
puts("Enter the author.");
fgets(current->author, 80, stdin);
puts("Enter the ISBN.");
fgets(current->ISBN, 80, stdin);

puts("Enter next book title (empty line to quit)");
prev = current;
}

Here's the part that writes to the file:

input_file = fopen("library.txt", "w"); 
printf("Printing list to file...\n");
while(current != NULL)
{
  fprintf(input_file,"%s%s%s", current->title, current->author, current->ISBN);
  //fputs(newline, input_file);    
}

That's the relevant part. The commented part I tried, but it put newlines all over, messing with the data that was already nicely formatted. Here's a little example of how the text file should look (ignore the coloring):

Title 1
Last, First
000000 (ISBN)

Title 2
Last, First
111111

etc.

When I add a book and the program writes it to the file, it adds it like this (left out ISBN for clarity):

...
Title 2
Last, First
First Added Book
Last, First
Second Added Title
Last, First
etc.

How can I get an empty line in between each book entry?

Answer 1

Why not just insert a newline-character (\\n) in this line?

fprintf(input_file,"%s%s%s", current->title, current->author, current->ISBN);

->

fprintf(input_file,"%s%s%s\n", current->title, current->author, current->ISBN);

FYI, if you add more \\n you get more empty lines.

Answer 2

1. Leaving the '\\n' in input . (see #4 also)
   This code wants to work with input that has its terminating '\\n' removed. @Lee Daniel Crocker

    while(fgets(input, 80, stdin) != NULL) { size_t len = strlen(input); // Note: under select circumstances, len will be 0. if (len > 0 && input[i-1] == '\\n') input[--len] = 0; // replace `&& input[0] != '\\n'` with if (len == 0) break; 

2. Add one or two '\\n' here. @midor

    fprintf(input_file,"%s%s%s\\n", ... 

3. Minor: simplify malloc() .

    // current = (struct book *)malloc(sizeof(struct book)); current = malloc(sizeof *current); 

4. Check return value on subsequent fgets() . Need to eliminate the trailing \\n' here too.

5. After malloc() consider initializing the entire structure.

    current = malloc(sizeof *current); if (current == NULL) Handle_OOM(); memset(current, 0, sizeof *current); // or current = calloc(1, sizeof *current);