Recursive function : abort-condition - c

Question

We need to create a binary tree which contains content of textfiles. The pointer selection_a and selection_b pointing to another textfile in the directory.
The structure of the textfiles is following:
line: Title
line: OptionA
line: OptionB
line: Text.
The first file is given as parameter while starting the program. All files should be saved at the beginning of the program. Then the text of the first file shows, and the user can input A or B to continue. Based on the selection, the text of File Option A/B is shown and the user can decide again.
The last file of a tree contains no Options: lines 2 and 3 are "-\n".
The problem is, this code only reads all the option A files of the first tree. It doesn't read in any B-Options. In the end, the program shows a memory access error.
I think the problem is that the readingRows function has no abort condition.
current->selection_a = readingRows(input_selection_a);
current->selection_b = readingRows(input_selection_b);
I know the code may be kind of chaotic, but we are beginners in programming. Hope anybody can help us to write an abort-condition.
The function should be aborted if the content of option A (line 3) is "-\n".
Here is the whole function:
struct story_file* readingRows(FILE *current_file)
{
char *buffer = fileSize(current_file);
char *delimiter = "\n";
char *lines = strtok(buffer, delimiter);
int line_counter = 0;
struct story_file *current = malloc(sizeof(struct story_file));
while(lines != NULL)
{
if(line_counter == 0)
{
current->title = lines;
}
else if(line_counter == 1)
{
char *filename_chapter_a = lines;
FILE *input_selection_a = fopen(filename_chapter_a, "r");
if(input_selection_a)
{
current->selection_a = readingRows(input_selection_a);
}
fclose(input_selection_a);
}
else if(line_counter == 2)
{
char *filename_chapter_b = lines;
FILE *input_selection_b = fopen(filename_chapter_b, "r");
if(input_selection_b)
{
current->selection_b = readingRows(input_selection_b);
}
fclose(input_selection_b);
}
else if (line_counter >= 3)
{
current->text = lines;
}
lines = strtok(NULL, delimiter);
line_counter++;
}
return current;
}

Answer 1

There are two items that define a terminating recursive function:
One or more base cases
Recursive calls that move toward a base case
Your code has one base case: while (lines!=NULL) {} return current;, it breaks the while loop when lines is NULL and returns current. In other words, within any particular call to your function, it only terminates when it reaches the end of a file.
Your code moves toward that base case as long as your files do not refer to each other in a loop. We know this because you always read a line, take an action according to your if-else block, and the read the next line. So you always move toward the end of each file you read.
But as you note, the issue is that you don't have a case to handle "no Options", being when lines 2 or 3 are "-\n". So right now, even though you move through files, you are always opening files in line 2. Unless a file is malformed and does not contain a line 2, your recursive call tree never ends. So you just need to add another base case that looks at whether the beginning of lines matches "-\n", and if it does, return before the recursive call. This will end that branch of your recursive tree.
Inside of your while loop, you will need code along the lines of:
if `line_counter` is `2` or `3`
if `lines` starts with your terminating sequence "-\n"
return current
else
`fopen` and make the recursive call
In the parent function that made the recursive call, it will move to the next line and continue as expected.
P.S. Make sure you use free for each malloc you do.