Thread: Why doesn't working?

This is the class Forum

Code:

class Forum
{
  char *name;
  int ID , subforumsnum , threadsnum;
  Forum **subforums  ;  //Array of indexes of subforums
  Forum *back ;
  Thread **threads;

public:
     //--------------constructor-destructor etc.
};

This is the class Thread

Code:

class Thread
{
 char *name , *creator_name;
 int ID,postsnum;
 bool locked,sticky;
 Forum *back;
 Post **posts;   //Array of indexes of posts included in thread class

public:
     void answer_to_post ( int newID, char *name, int pID );
     //------------constructor-destructor etc.
};

And here is the function answer_to_post

Code:

void Thread :: answer_to_post ( int newID, char *cname, int pID )
{
  char *newcontent;
  Post **temp;            //temporary array for posts
  
  cout<<"Type your answer to the post"<<endl;
  cin>>newcontent;

  temp = new Post *[postsnum+1];   //Expand the array by one more cell from the posts array
  for( int i=0 ; i<postsnum ; i++ )
       temp[i] = posts[i];                      //Copy the posts to temp

  delete[] posts;     //Delete the old posts array

  //Store the new post to the new position of temp array
  temp[postsnum] = new Post ( newID, cname, pID, newcontent );

  postsnum++;    //Increase the number of posts by one
  posts = new Post *[postsnum];    //Create new array same size as temp

  for( int i=0 ; i<postsnum ; i++ )
       posts[i] = temp[i];                   //Copy temp array to posts array

  delete[] temp;    //Delete temp array
}

The basic idea is to make a temporary array (temp) in order store indexes of posts classes, expand the posts array by one cell and store the new post into the last cell.
In reality it is a "dynamic" array which stores post classes.

I do not know why it does not working.
After using it all cells had the same class in every cell.

Thanks

Originally Posted by ch4

This is the class Forum

Code:

class Thread
{
  char *name;
  int ID , subforumsnum , threadsnum;
  Forum **subforums  ;  //Array of indexes of subforums
  Forum *back ;
  Thread **threads;

public:
     //--------------constructor-destructor etc.
};

You sure about that? Doesn't look like the Forum class to me.

Code:

char *newcontent;
...
cout<<"Type your answer to the post"<<endl;
cin>>newcontent;

What do you expect that to do? You haven't allocated any space for newcontent so it's pointing to some random location where you're dumping the user's answer.

Are you not allowed to use a vector to store your Posts? That could greatly simplify things.

There is no problem in allocating the newcontent, i've change the way of allocation.
The function runs without problems (no warning,no errors...)

Your code neither allocates nor releases the newcontent string. If you have it, don't just omit it.

but i can understand why every cell of the new potst array is filled with only one class.

How many do you want there to be, then?

The only thing I can see is that you shouldn't allocate the array of Post pointers twice. Simple
posts = temp; and not deleting temp should be enough.

Another problem is, that unless you are not allowed to use C++ standard libraries, there's too much complexity (from manually managing memory). From design point of view all these classes are doing too much: providing high level functionality and doing the low level job of memory management. If these were separated (by using std::vector, std::string or similar classes - you can write your own if you need to), it would be much easier to follow the high-level logic of the high-level classes.

Code:

void Thread :: answer_to_post ( int newID, char *cname, int pID )
{
  string newcontent;
  cout<<"Type your answer to the post"<<endl;
  getline(cin, newcontent); //or were you asking about this
  posts.push_back(Post(newID, cname, pID, newcontent ));
}

This is what the same code might look like. Note that there is no visible low-level code, and each line of code performs a clearly readable high-level operation.

I am new in C++ so i 've asked your help.

In reality this is a homework and i'm free to use every library and every function i like/need. I've asked to make a system which consists of forums - threads - posts - users etc. My first idea was a forum with subforums into double linked lists but i was afraid of the hard way of accessing them, so i prefer arrays with pointer to the classes.

Thanks Anon

If you have such an assignment you can't be a complete beginner. As you can see there is a lot to gain from separating high-level and low-level code, especially if the language provides objects that do the low-level tasks for you.

The above function wouldn't need a single change if posts was a std::list (doubly linked list) instead of std::vector. (But other code that took advantage of the random access of vectors might.)

And if you really want to get more experience with low-level code (managing dynamic arrays), it would be possible to write your own array class and as long as it had the push_back function, the answer_to_post method would still be exactly the same.