I am trying to write some C code that appends a line of text to a file, and then simply display it line by line. When I open the file in append mode and add a line using fprintf, the line gets added and I can see it when I open the file with a text editor. However when I call a function to display all lines (which works fine before the new text is appended), I get all the lines until the last but excluding the new appended line.

Here is the code I'm working with. The first function just adds a new line, and the second function just reads all the lines. The read_csv() works initially when I haven't appended any lines through code and have just used a text editor to add my initial lines.

void add_record(const char* csv_filename)

 FILE *f = fopen(csv_filename,"at");
 char str="My appended line "
 fprintf(f,"%s",str);
 fclose(f);


void read_csv(const char* csv_filename)

 FILE *f = fopen(csv_filename,"rt");
 char str[MAX];
 fgets(str,MAX,f);
 while(!feof(f))
 fputs(str,stdout);
 fputs("n",stdout);
 fgets(str,MAX,f);
 
 fclose(f);

Now I found two fixes to my problem but I don't exactly understand why they work.

Fix 1 : Adding an extra fgets() prints the missing appending line when I'm trying to display it, however when I use it to display my original text file it prints the last line twice..so not a good fix.

fgets(str,MAX,f)
while(!feof(f))
 fputs(str,stdout);
 fputs("n",stdout);
 fgets(str,MAX,f);
 
 fgets(str,MAX,f)

Fix 2 : Adding a new line character at the along with the string appended fixes the problem perfectly and everything is smooth. All the lines get displayed when I call read_csv().

char str="My appended line "
 fprintf(f,"%sn",str)

Looking at the docs for fgets(), it says it reads until either a new line character or eof has reached(whichever occurs first), so I don't understand why my appended line get ignored by fgets().

When fgets() reaches the last line(which it skips) the situation I presume is something like this: it gets a string with " text text text eof",and it breaks out the loop skipping the print statement. But then when I use an extra fgets() outside the while loop it works. Also when I add a new line and the situation is a string like " text text text n eof", it doesn't quit the loop and goes on to display it.

I would really appreciate if I could get some info on what is happening and why these two fixes work. I suspect it is something to do with the feof detecting an eof or some specifics about fgets but I couldn't find anything satisfactory online.

Thank you so much in advance for taking the time to read and respond.